From e51565c7e596ac4f97b64708873451d3a5aace36 Mon Sep 17 00:00:00 2001
From: monojenkins <jo.shields+jenkins@xamarin.com>
Date: Sat, 25 Nov 2017 23:34:52 +0100
Subject: [msvc] Update csproj files (#6100)

---
 mcs/class/Accessibility/Accessibility-net_4_x.csproj   |  1 +
 .../Commons.Xml.Relaxng-net_4_x.csproj                 |  1 +
 mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj           |  1 +
 .../CustomMarshalers/CustomMarshalers-net_4_x.csproj   |  1 +
 .../Facades_Microsoft.Win32.Primitives-net_4_x.csproj  |  1 +
 ...crosoft.Win32.Registry.AccessControl-net_4_x.csproj |  1 +
 .../Facades_Microsoft.Win32.Registry-net_4_x.csproj    |  1 +
 .../Facades_System.AppContext-net_4_x.csproj           |  1 +
 ...acades_System.Collections.Concurrent-net_4_x.csproj |  1 +
 ...acades_System.Collections.NonGeneric-net_4_x.csproj |  1 +
 ...cades_System.Collections.Specialized-net_4_x.csproj |  1 +
 .../Facades_System.Collections-net_4_x.csproj          |  1 +
 ...es_System.ComponentModel.Annotations-net_4_x.csproj |  1 +
 ...ystem.ComponentModel.EventBasedAsync-net_4_x.csproj |  1 +
 ...des_System.ComponentModel.Primitives-net_4_x.csproj |  1 +
 ..._System.ComponentModel.TypeConverter-net_4_x.csproj |  1 +
 .../Facades_System.ComponentModel-net_4_x.csproj       |  1 +
 .../Facades_System.Console-net_4_x.csproj              |  1 +
 .../Facades_System.Data.Common-net_4_x.csproj          |  1 +
 .../Facades_System.Data.SqlClient-net_4_x.csproj       |  1 +
 ...Facades_System.Diagnostics.Contracts-net_4_x.csproj |  1 +
 .../Facades_System.Diagnostics.Debug-net_4_x.csproj    |  1 +
 ...s_System.Diagnostics.FileVersionInfo-net_4_x.csproj |  1 +
 .../Facades_System.Diagnostics.Process-net_4_x.csproj  |  1 +
 ...acades_System.Diagnostics.StackTrace-net_4_x.csproj |  1 +
 ....Diagnostics.TextWriterTraceListener-net_4_x.csproj |  1 +
 .../Facades_System.Diagnostics.Tools-net_4_x.csproj    |  1 +
 ...acades_System.Diagnostics.TraceEvent-net_4_x.csproj |  1 +
 ...cades_System.Diagnostics.TraceSource-net_4_x.csproj |  1 +
 .../Facades_System.Diagnostics.Tracing-net_4_x.csproj  |  1 +
 .../Facades_System.Drawing.Primitives-net_4_x.csproj   |  1 +
 .../Facades_System.Dynamic.Runtime-net_4_x.csproj      |  1 +
 ...cades_System.Globalization.Calendars-net_4_x.csproj |  1 +
 ...ades_System.Globalization.Extensions-net_4_x.csproj |  1 +
 .../Facades_System.Globalization-net_4_x.csproj        |  1 +
 ...acades_System.IO.Compression.ZipFile-net_4_x.csproj |  1 +
 ...s_System.IO.FileSystem.AccessControl-net_4_x.csproj |  1 +
 ...cades_System.IO.FileSystem.DriveInfo-net_4_x.csproj |  1 +
 ...ades_System.IO.FileSystem.Primitives-net_4_x.csproj |  1 +
 ...Facades_System.IO.FileSystem.Watcher-net_4_x.csproj |  1 +
 .../Facades_System.IO.FileSystem-net_4_x.csproj        |  1 +
 .../Facades_System.IO.IsolatedStorage-net_4_x.csproj   |  1 +
 .../Facades_System.IO.MemoryMappedFiles-net_4_x.csproj |  1 +
 .../Facades_System.IO.Pipes-net_4_x.csproj             |  1 +
 ...ades_System.IO.UnmanagedMemoryStream-net_4_x.csproj |  1 +
 .../Facades/System.IO/Facades_System.IO-net_4_x.csproj |  1 +
 .../Facades_System.Linq.Expressions-net_4_x.csproj     |  1 +
 .../Facades_System.Linq.Parallel-net_4_x.csproj        |  1 +
 .../Facades_System.Linq.Queryable-net_4_x.csproj       |  1 +
 .../System.Linq/Facades_System.Linq-net_4_x.csproj     |  1 +
 ...des_System.Net.AuthenticationManager-net_4_x.csproj |  1 +
 .../Facades_System.Net.Cache-net_4_x.csproj            |  1 +
 .../Facades_System.Net.HttpListener-net_4_x.csproj     |  1 +
 .../Facades_System.Net.Mail-net_4_x.csproj             |  1 +
 .../Facades_System.Net.NameResolution-net_4_x.csproj   |  1 +
 ...acades_System.Net.NetworkInformation-net_4_x.csproj |  1 +
 .../Facades_System.Net.Primitives-net_4_x.csproj       |  1 +
 .../Facades_System.Net.Requests-net_4_x.csproj         |  1 +
 .../Facades_System.Net.Security-net_4_x.csproj         |  1 +
 .../Facades_System.Net.ServicePoint-net_4_x.csproj     |  1 +
 .../Facades_System.Net.Sockets-net_4_x.csproj          |  1 +
 .../Facades_System.Net.Utilities-net_4_x.csproj        |  1 +
 ...cades_System.Net.WebHeaderCollection-net_4_x.csproj |  1 +
 ...Facades_System.Net.WebSockets.Client-net_4_x.csproj |  1 +
 .../Facades_System.Net.WebSockets-net_4_x.csproj       |  1 +
 .../Facades_System.ObjectModel-net_4_x.csproj          |  1 +
 ..._System.Reflection.Emit.ILGeneration-net_4_x.csproj |  1 +
 ...s_System.Reflection.Emit.Lightweight-net_4_x.csproj |  1 +
 .../Facades_System.Reflection.Emit-net_4_x.csproj      |  1 +
 ...Facades_System.Reflection.Extensions-net_4_x.csproj |  1 +
 ...Facades_System.Reflection.Primitives-net_4_x.csproj |  1 +
 ...des_System.Reflection.TypeExtensions-net_4_x.csproj |  1 +
 .../Facades_System.Reflection-net_4_x.csproj           |  1 +
 ...acades_System.Resources.ReaderWriter-net_4_x.csproj |  1 +
 ...des_System.Resources.ResourceManager-net_4_x.csproj |  1 +
 ...tem.Runtime.CompilerServices.VisualC-net_4_x.csproj |  1 +
 .../Facades_System.Runtime.Extensions-net_4_x.csproj   |  1 +
 .../Facades_System.Runtime.Handles-net_4_x.csproj      |  1 +
 ...e.InteropServices.RuntimeInformation-net_4_x.csproj |  1 +
 ...ntime.InteropServices.WindowsRuntime-net_4_x.csproj |  1 +
 ...cades_System.Runtime.InteropServices-net_4_x.csproj |  1 +
 .../Facades_System.Runtime.Numerics-net_4_x.csproj     |  1 +
 ...es_System.Runtime.Serialization.Json-net_4_x.csproj |  1 +
 ...tem.Runtime.Serialization.Primitives-net_4_x.csproj |  1 +
 ...des_System.Runtime.Serialization.Xml-net_4_x.csproj |  1 +
 .../Facades_System.Runtime-net_4_x.csproj              |  1 +
 ...acades_System.Security.AccessControl-net_4_x.csproj |  1 +
 .../Facades_System.Security.Claims-net_4_x.csproj      |  1 +
 ...tem.Security.Cryptography.Algorithms-net_4_x.csproj |  1 +
 ...em.Security.Cryptography.DeriveBytes-net_4_x.csproj |  1 +
 ...ystem.Security.Cryptography.Encoding-net_4_x.csproj |  1 +
 ...Security.Cryptography.Encryption.Aes-net_4_x.csproj |  1 +
 ...ptography.Encryption.ECDiffieHellman-net_4_x.csproj |  1 +
 ...curity.Cryptography.Encryption.ECDsa-net_4_x.csproj |  1 +
 ...tem.Security.Cryptography.Encryption-net_4_x.csproj |  1 +
 ...rity.Cryptography.Hashing.Algorithms-net_4_x.csproj |  1 +
 ...System.Security.Cryptography.Hashing-net_4_x.csproj |  1 +
 ...tem.Security.Cryptography.Primitives-net_4_x.csproj |  1 +
 ....Security.Cryptography.ProtectedData-net_4_x.csproj |  1 +
 ...des_System.Security.Cryptography.RSA-net_4_x.csproj |  1 +
 ...y.Cryptography.RandomNumberGenerator-net_4_x.csproj |  1 +
 ...curity.Cryptography.X509Certificates-net_4_x.csproj |  1 +
 ...es_System.Security.Principal.Windows-net_4_x.csproj |  1 +
 .../Facades_System.Security.Principal-net_4_x.csproj   |  1 +
 ...Facades_System.Security.SecureString-net_4_x.csproj |  1 +
 .../Facades_System.ServiceModel.Duplex-net_4_x.csproj  |  1 +
 .../Facades_System.ServiceModel.Http-net_4_x.csproj    |  1 +
 .../Facades_System.ServiceModel.NetTcp-net_4_x.csproj  |  1 +
 ...cades_System.ServiceModel.Primitives-net_4_x.csproj |  1 +
 ...Facades_System.ServiceModel.Security-net_4_x.csproj |  1 +
 ...tem.ServiceProcess.ServiceController-net_4_x.csproj |  1 +
 ...cades_System.Text.Encoding.CodePages-net_4_x.csproj |  1 +
 ...ades_System.Text.Encoding.Extensions-net_4_x.csproj |  1 +
 .../Facades_System.Text.Encoding-net_4_x.csproj        |  1 +
 ...cades_System.Text.RegularExpressions-net_4_x.csproj |  1 +
 ...cades_System.Threading.AccessControl-net_4_x.csproj |  1 +
 .../Facades_System.Threading.Overlapped-net_4_x.csproj |  1 +
 ...ades_System.Threading.Tasks.Parallel-net_4_x.csproj |  1 +
 .../Facades_System.Threading.Tasks-net_4_x.csproj      |  1 +
 .../Facades_System.Threading.Thread-net_4_x.csproj     |  1 +
 .../Facades_System.Threading.ThreadPool-net_4_x.csproj |  1 +
 .../Facades_System.Threading.Timer-net_4_x.csproj      |  1 +
 .../Facades_System.Threading-net_4_x.csproj            |  1 +
 .../Facades_System.ValueTuple-net_4_x.csproj           |  1 +
 .../Facades_System.Xml.ReaderWriter-net_4_x.csproj     |  1 +
 .../Facades_System.Xml.XDocument-net_4_x.csproj        |  1 +
 .../Facades_System.Xml.XPath.XDocument-net_4_x.csproj  |  1 +
 .../Facades_System.Xml.XPath-net_4_x.csproj            |  1 +
 .../Facades_System.Xml.XmlDocument-net_4_x.csproj      |  1 +
 .../Facades_System.Xml.XmlSerializer-net_4_x.csproj    |  1 +
 .../Facades_System.Xml.Xsl.Primitives-net_4_x.csproj   |  1 +
 .../netstandard/Facades_netstandard-net_4_x.csproj     |  1 +
 mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj             |  1 +
 mcs/class/I18N/Common/I18N-net_4_x.csproj              |  1 +
 mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj     |  1 +
 mcs/class/I18N/Other/I18N.Other-net_4_x.csproj         |  1 +
 mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj           |  1 +
 mcs/class/I18N/West/I18N.West-net_4_x.csproj           |  1 +
 mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj     |  1 +
 .../ICSharpCode.SharpZipLib-net_4_x.csproj             |  1 +
 .../Microsoft.Build.Engine-net_4_x.csproj              |  1 +
 .../Microsoft.Build.Framework-net_4_x.csproj           |  1 +
 .../Microsoft.Build.Tasks-net_4_x.csproj               |  1 +
 .../Microsoft.Build.Utilities-net_4_x.csproj           |  1 +
 .../Microsoft.Build/Microsoft.Build-net_4_x.csproj     |  1 +
 .../Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj   |  2 +-
 .../Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj |  1 +
 .../Microsoft.Web.Infrastructure-net_4_x.csproj        |  1 +
 .../Mono.Btls.Interface-net_4_x.csproj                 |  1 +
 mcs/class/Mono.C5/Mono.C5-net_4_x.csproj               |  1 +
 mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj       |  1 +
 mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj         |  1 +
 mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj |  1 +
 mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj         |  1 +
 .../Mono.CodeContracts-net_4_x.csproj                  |  1 +
 .../Mono.CompilerServices.SymbolWriter-net_4_x.csproj  |  1 +
 .../Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj   |  1 +
 mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj   |  1 +
 .../Mono.Debugger.Soft-net_4_x.csproj                  |  1 +
 mcs/class/Mono.Http/Mono.Http-net_4_x.csproj           |  1 +
 .../Mono.Management/Mono.Management-net_4_x.csproj     |  1 +
 .../Mono.Messaging.RabbitMQ-net_4_x.csproj             |  1 +
 mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj |  1 +
 mcs/class/Mono.Options/Mono.Options-net_4_x.csproj     |  1 +
 mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj   |  1 +
 mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj         |  1 +
 .../Mono.Profiler.Log/Mono.Profiler.Log-net_4_x.csproj |  1 +
 .../Mono.Security.Win32-net_4_x.csproj                 |  1 +
 mcs/class/Mono.Security/Mono.Security-net_4_x.csproj   |  1 +
 mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj           |  1 +
 mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj   |  1 +
 .../Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj     |  1 +
 .../Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj |  1 +
 .../Novell.Directory.Ldap-net_4_x.csproj               |  1 +
 mcs/class/PEAPI/PEAPI-net_4_x.csproj                   |  1 +
 .../src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj   |  1 +
 .../src/client/RabbitMQ.Client-net_4_x.csproj          |  1 +
 mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj   |  1 +
 .../System.ComponentModel.Composition-net_4_x.csproj   |  1 +
 ...ystem.ComponentModel.DataAnnotations-net_4_x.csproj |  1 +
 .../System.Configuration.Install-net_4_x.csproj        |  1 +
 .../System.Configuration-net_4_x.csproj                |  1 +
 mcs/class/System.Core/System.Core-net_4_x.csproj       |  1 +
 .../System.Data.DataSetExtensions-net_4_x.csproj       |  1 +
 .../System.Data.Entity-net_4_x.csproj                  |  1 +
 .../System.Data.Linq/System.Data.Linq-net_4_x.csproj   |  1 +
 .../System.Data.OracleClient-net_4_x.csproj            |  1 +
 .../System.Data.Services.Client-net_4_x.csproj         |  1 +
 .../System.Data.Services-net_4_x.csproj                |  1 +
 mcs/class/System.Data/System.Data-net_4_x.csproj       |  1 +
 .../System.Deployment/System.Deployment-net_4_x.csproj |  1 +
 mcs/class/System.Design/System.Design-net_4_x.csproj   |  1 +
 .../System.Design-plaindesign-net_4_x.csproj           |  1 +
 .../System.DirectoryServices.Protocols-net_4_x.csproj  |  1 +
 .../System.DirectoryServices-net_4_x.csproj            |  1 +
 .../System.Drawing.Design-net_4_x.csproj               |  1 +
 mcs/class/System.Drawing/System.Drawing-net_4_x.csproj |  1 +
 mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj |  1 +
 .../System.EnterpriseServices-net_4_x.csproj           |  1 +
 .../System.IO.Compression.FileSystem-net_4_x.csproj    |  1 +
 .../System.IO.Compression-net_4_x.csproj               |  1 +
 .../System.IdentityModel.Selectors-net_4_x.csproj      |  1 +
 .../System.IdentityModel-net_4_x.csproj                |  1 +
 .../System.Json.Microsoft-net_4_x.csproj               |  1 +
 mcs/class/System.Json/System.Json-net_4_x.csproj       |  1 +
 .../System.Management/System.Management-net_4_x.csproj |  1 +
 .../System.Messaging/System.Messaging-net_4_x.csproj   |  1 +
 .../System.Net.Http.Formatting-net_4_x.csproj          |  1 +
 .../System.Net.Http.WebRequest-net_4_x.csproj          |  1 +
 .../System.Net.Http/System.Net.Http-net_4_x.csproj     |  1 +
 mcs/class/System.Net/System.Net-net_4_x.csproj         |  1 +
 .../System.Numerics.Vectors-net_4_x.csproj             |  1 +
 .../System.Numerics/System.Numerics-net_4_x.csproj     |  1 +
 .../System.Reactive.Core-net_4_x.csproj                |  1 +
 .../System.Reactive.Debugger-net_4_x.csproj            |  1 +
 .../System.Reactive.Experimental-net_4_x.csproj        |  1 +
 .../System.Reactive.Interfaces-net_4_x.csproj          |  1 +
 .../System.Reactive.Linq-net_4_x.csproj                |  1 +
 .../System.Reactive.Observable.Aliases-net_4_x.csproj  |  1 +
 .../System.Reactive.PlatformServices-net_4_x.csproj    |  1 +
 .../System.Reactive.Providers-net_4_x.csproj           |  1 +
 .../System.Reactive.Runtime.Remoting-net_4_x.csproj    |  1 +
 .../System.Reactive.Windows.Forms-net_4_x.csproj       |  1 +
 .../System.Reactive.Windows.Threading-net_4_x.csproj   |  1 +
 .../System.Reflection.Context-net_4_x.csproj           |  1 +
 .../System.Runtime.Caching-net_4_x.csproj              |  1 +
 .../System.Runtime.DurableInstancing-net_4_x.csproj    |  1 +
 .../System.Runtime.Remoting-net_4_x.csproj             |  1 +
 ...untime.Serialization.Formatters.Soap-net_4_x.csproj |  1 +
 .../System.Runtime.Serialization-net_4_x.csproj        |  1 +
 .../System.Security/System.Security-net_4_x.csproj     |  1 +
 .../System.ServiceModel.Activation-net_4_x.csproj      |  1 +
 .../System.ServiceModel.Discovery-net_4_x.csproj       |  1 +
 .../System.ServiceModel.Internals-net_4_x.csproj       |  1 +
 .../System.ServiceModel.Routing-net_4_x.csproj         |  1 +
 .../System.ServiceModel.Web-net_4_x.csproj             |  1 +
 .../System.ServiceModel-net_4_x.csproj                 |  1 +
 .../System.ServiceModel-plainservice-net_4_x.csproj    |  1 +
 .../System.ServiceProcess-net_4_x.csproj               |  1 +
 .../System.Threading.Tasks.Dataflow-net_4_x.csproj     |  1 +
 .../System.Transactions-net_4_x.csproj                 |  1 +
 .../System.Web.Abstractions-net_4_x.csproj             |  1 +
 .../System.Web.ApplicationServices-net_4_x.csproj      |  1 +
 .../System.Web.DynamicData-net_4_x.csproj              |  1 +
 .../System.Web.Extensions.Design-net_4_x.csproj        |  1 +
 .../System.Web.Extensions-net_4_x.csproj               |  1 +
 .../System.Web.Http.SelfHost-net_4_x.csproj            |  1 +
 .../System.Web.Http.WebHost-net_4_x.csproj             |  1 +
 .../System.Web.Http/System.Web.Http-net_4_x.csproj     |  1 +
 .../System.Web.Mobile/System.Web.Mobile-net_4_x.csproj |  1 +
 .../System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj     |  1 +
 .../System.Web.Razor/System.Web.Razor-net_4_x.csproj   |  1 +
 .../System.Web.RegularExpressions-net_4_x.csproj       |  1 +
 .../System.Web.Routing-net_4_x.csproj                  |  1 +
 .../System.Web.Services-net_4_x.csproj                 |  1 +
 .../System.Web.WebPages.Deployment-net_4_x.csproj      |  1 +
 .../System.Web.WebPages.Razor-net_4_x.csproj           |  1 +
 .../System.Web.WebPages-net_4_x.csproj                 |  1 +
 mcs/class/System.Web/System.Web-net_4_x.csproj         |  1 +
 .../System.Web/System.Web-plainweb-net_4_x.csproj      |  1 +
 ...stem.Windows.Forms.DataVisualization-net_4_x.csproj |  1 +
 .../System.Windows.Forms-net_4_x.csproj                |  1 +
 mcs/class/System.Windows/System.Windows-net_4_x.csproj |  1 +
 .../System.Workflow.Activities-net_4_x.csproj          |  1 +
 .../System.Workflow.ComponentModel-net_4_x.csproj      |  1 +
 .../System.Workflow.Runtime-net_4_x.csproj             |  1 +
 mcs/class/System.XML/System.Xml-bare-net_4_x.csproj    |  1 +
 mcs/class/System.XML/System.Xml-net_4_x.csproj         |  1 +
 mcs/class/System.Xaml/System.Xaml-net_4_x.csproj       |  1 +
 .../System.Xml.Linq/System.Xml.Linq-net_4_x.csproj     |  1 +
 .../System.Xml.Serialization-net_4_x.csproj            |  1 +
 mcs/class/System/System-bare-net_4_x.csproj            |  6 ++++++
 mcs/class/System/System-net_4_x.csproj                 |  6 ++++++
 mcs/class/System/System-secxml-net_4_x.csproj          |  6 ++++++
 .../SystemWebTestShim/SystemWebTestShim-net_4_x.csproj |  1 +
 mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj |  1 +
 mcs/class/WindowsBase/WindowsBase-net_4_x.csproj       |  1 +
 mcs/class/corlib/corlib-net_4_x.csproj                 | 18 +++++++++++++++---
 .../legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj |  1 +
 mcs/class/monodoc/monodoc-net_4_x.csproj               |  1 +
 280 files changed, 309 insertions(+), 4 deletions(-)

(limited to 'mcs/class')

diff --git a/mcs/class/Accessibility/Accessibility-net_4_x.csproj b/mcs/class/Accessibility/Accessibility-net_4_x.csproj
index 184dd24b546..c2ffc1ee656 100644
--- a/mcs/class/Accessibility/Accessibility-net_4_x.csproj
+++ b/mcs/class/Accessibility/Accessibility-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E51283DC-7090-479E-B723-01C0953F18EA}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj b/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj
index b49d7010751..344f8a380c2 100644
--- a/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj
+++ b/mcs/class/Commons.Xml.Relaxng/Commons.Xml.Relaxng-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{FFFE76FE-98EE-4FF7-81D9-35C0FE1D3718}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj b/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj
index 1a3ace6659d..969a7932a82 100644
--- a/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj
+++ b/mcs/class/Cscompmgd/Cscompmgd-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2AB43CEE-0BE1-46EF-971E-3678330BEA13}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj b/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj
index 4d8050eee98..cc655e111d6 100644
--- a/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj
+++ b/mcs/class/CustomMarshalers/CustomMarshalers-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{6D021ADB-0407-42C9-9CC9-6613D94C61AE}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj b/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj
index 74a03527842..dc52dab856a 100644
--- a/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/Microsoft.Win32.Primitives/Facades_Microsoft.Win32.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{699E0DB5-EDD0-4E6A-87C9-D396DCDAF620}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj b/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj
index de874d1a08e..3651bd5cd0c 100644
--- a/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/Microsoft.Win32.Registry.AccessControl/Facades_Microsoft.Win32.Registry.AccessControl-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{7B15C4D7-8C02-408E-9EFB-5E9E9FB4410D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj b/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj
index 0e137b9cdc1..8fcdb2e0950 100644
--- a/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj
+++ b/mcs/class/Facades/Microsoft.Win32.Registry/Facades_Microsoft.Win32.Registry-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{160B5B14-7A25-458E-B83F-35632C832866}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj b/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj
index 166f38f7b07..b1ad6029a34 100644
--- a/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj
+++ b/mcs/class/Facades/System.AppContext/Facades_System.AppContext-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{B6B7A903-D696-43CF-AC42-39DCAAB00B9D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj b/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj
index 5245963a9cd..3789e557555 100644
--- a/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections.Concurrent/Facades_System.Collections.Concurrent-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{EFD0287C-3651-4D42-B8CA-430776CB1E6D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj b/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj
index 9d34a904b52..5cf5e20500d 100644
--- a/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections.NonGeneric/Facades_System.Collections.NonGeneric-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5F686C07-72CE-4A42-93B1-52B31227C3BB}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj b/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj
index 802f18a8ab4..c3e45e78563 100644
--- a/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections.Specialized/Facades_System.Collections.Specialized-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5A238E60-587C-4C5C-8CA4-0443B1DBF1F6}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj b/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj
index c3043b33b8e..00fe7bee33f 100644
--- a/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj
+++ b/mcs/class/Facades/System.Collections/Facades_System.Collections-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2597261D-EC05-4333-928D-1CA44AB1A5D2}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj
index ccc830c7cdf..5efa98e4f45 100644
--- a/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.Annotations/Facades_System.ComponentModel.Annotations-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{B26700A5-4A9A-4358-8C84-51AD67C706BA}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj
index 83a16b0a3a5..6f36d282641 100644
--- a/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.EventBasedAsync/Facades_System.ComponentModel.EventBasedAsync-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{6871A822-F21C-4C0E-B97B-178FF6C3DB46}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj
index dc22a7cad46..d03995129a3 100644
--- a/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.Primitives/Facades_System.ComponentModel.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{1DF9021C-DC67-4D7B-BEC9-10D7FBC12972}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj
index 30758b0d57c..a154ba9a5fc 100644
--- a/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel.TypeConverter/Facades_System.ComponentModel.TypeConverter-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{FC19760B-00FF-4242-9760-9C8E9C87CCFB}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj b/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj
index c9680a56d61..e5349646a61 100644
--- a/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj
+++ b/mcs/class/Facades/System.ComponentModel/Facades_System.ComponentModel-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{3FA73846-3666-4769-B431-1A7538B08F39}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj b/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj
index 03703bca865..5d77042306d 100644
--- a/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj
+++ b/mcs/class/Facades/System.Console/Facades_System.Console-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{6207AADB-0592-4B52-B71E-3565196EE893}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj b/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj
index e8c9494131a..8fe5cdacef7 100644
--- a/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj
+++ b/mcs/class/Facades/System.Data.Common/Facades_System.Data.Common-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{360CDD70-6108-4406-9433-7BB178B0C3E3}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj b/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj
index 4019872b113..3d35a30ab57 100644
--- a/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj
+++ b/mcs/class/Facades/System.Data.SqlClient/Facades_System.Data.SqlClient-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{575873BD-22DA-4A36-ABBD-B074EFEAB3AD}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj
index f7a8d51f60e..05b0365d459 100644
--- a/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Contracts/Facades_System.Diagnostics.Contracts-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{8892480E-A4C6-4C4C-8722-21C5483F8851}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj
index 7728b281772..205d1c3adf6 100644
--- a/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Debug/Facades_System.Diagnostics.Debug-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj
index c2d9a532b22..a832ef92be4 100644
--- a/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.FileVersionInfo/Facades_System.Diagnostics.FileVersionInfo-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj
index 9505eb56c65..630adee1994 100644
--- a/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Process/Facades_System.Diagnostics.Process-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj
index 9940a5eb3c6..12273b8d5d4 100644
--- a/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.StackTrace/Facades_System.Diagnostics.StackTrace-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{871BE2C6-2F56-4E05-93E8-9B3FDD4711DB}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj
index 183bf7fa802..2eb3e647629 100644
--- a/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.TextWriterTraceListener/Facades_System.Diagnostics.TextWriterTraceListener-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{EE8443AB-125D-4055-981A-143FB827C23C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj
index ce904941ca0..3a244dd2a2e 100644
--- a/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Tools/Facades_System.Diagnostics.Tools-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5B299463-3E19-48C1-8625-31E12E1CC146}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj
index 30df5a296db..a4829eb85ad 100644
--- a/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.TraceEvent/Facades_System.Diagnostics.TraceEvent-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{6460F8E8-775E-46B6-99E5-B48390591515}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj
index 8ea1bfdbc0f..bf04b090a3e 100644
--- a/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.TraceSource/Facades_System.Diagnostics.TraceSource-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{530F1E68-3237-49E6-8D3B-06332F5AC055}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj b/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj
index 95945bce18b..632e9b3eb98 100644
--- a/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj
+++ b/mcs/class/Facades/System.Diagnostics.Tracing/Facades_System.Diagnostics.Tracing-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{B33966AB-7211-43B4-B5C0-3F818869CB08}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj
index fc146ae91aa..9f0b458abc8 100644
--- a/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Drawing.Primitives/Facades_System.Drawing.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{1AFDB281-5FB8-48A9-8694-7F515D835862}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj b/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj
index fec9ddaf01b..fdb98e54216 100644
--- a/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj
+++ b/mcs/class/Facades/System.Dynamic.Runtime/Facades_System.Dynamic.Runtime-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E48CEF36-3218-477B-A8B5-014519207FF2}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj b/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj
index 9851d0f75e1..258b329e731 100644
--- a/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj
+++ b/mcs/class/Facades/System.Globalization.Calendars/Facades_System.Globalization.Calendars-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{BC71DA11-382F-459A-B3C3-F2F4267974FB}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj
index 2499318dd4f..c34fa46aa98 100644
--- a/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Globalization.Extensions/Facades_System.Globalization.Extensions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{B875622B-BEA2-4D1C-8242-3A1FCECF5890}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj b/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj
index fa666d31de0..fcae7951326 100644
--- a/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj
+++ b/mcs/class/Facades/System.Globalization/Facades_System.Globalization-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5F313CA5-F0FC-4EA3-AC8D-8EF1C7FC8ABE}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj b/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj
index b792acf5a12..3654604017c 100644
--- a/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.Compression.ZipFile/Facades_System.IO.Compression.ZipFile-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{A8EB5499-FA67-4049-AA0A-241D82DA975C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj
index b11eeda1084..74e1a29c909 100644
--- a/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.AccessControl/Facades_System.IO.FileSystem.AccessControl-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{321A53F3-A681-4CA5-A093-1C6650243F6A}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj
index e6666d22f8c..aafe92970d8 100644
--- a/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.DriveInfo/Facades_System.IO.FileSystem.DriveInfo-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{121F835D-CD32-4C19-ABA7-25EF4B84773F}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj
index f5792c31186..f7b99456d51 100644
--- a/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.Primitives/Facades_System.IO.FileSystem.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5DF20007-FD1D-4BD8-A492-D1C4F7CAD2BF}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj
index 49642ca0309..cc69e24fb8b 100644
--- a/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem.Watcher/Facades_System.IO.FileSystem.Watcher-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{44647FAA-F785-44DE-B6B2-ABC2B9768233}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj b/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj
index 176a7f4a90b..83a13e69034 100644
--- a/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.FileSystem/Facades_System.IO.FileSystem-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj b/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj
index 5f674f54865..6eec76de49a 100644
--- a/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.IsolatedStorage/Facades_System.IO.IsolatedStorage-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{A9B2D389-B9E5-4B0F-8115-2AADF285D217}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj b/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj
index c675865fd32..bacc5fae685 100644
--- a/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.MemoryMappedFiles/Facades_System.IO.MemoryMappedFiles-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj b/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj
index d4305457bdf..d72e5332549 100644
--- a/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.Pipes/Facades_System.IO.Pipes-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj b/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj
index 44f204cceb9..9b96a2fd63d 100644
--- a/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO.UnmanagedMemoryStream/Facades_System.IO.UnmanagedMemoryStream-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj b/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj
index f497741d1d2..9dd17395cea 100644
--- a/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj
+++ b/mcs/class/Facades/System.IO/Facades_System.IO-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj b/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj
index dea56bacf61..04b240c5ff1 100644
--- a/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq.Expressions/Facades_System.Linq.Expressions-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj b/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj
index 59d18ab9b36..67e1616130b 100644
--- a/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq.Parallel/Facades_System.Linq.Parallel-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj b/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj
index 4c613cdfb32..0509ddc9f23 100644
--- a/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq.Queryable/Facades_System.Linq.Queryable-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj b/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj
index 00328d988ca..d98bd71efb2 100644
--- a/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj
+++ b/mcs/class/Facades/System.Linq/Facades_System.Linq-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj b/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj
index 994bf113ad1..9c8ef4121b5 100644
--- a/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.AuthenticationManager/Facades_System.Net.AuthenticationManager-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj b/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj
index 6fe401ba7ca..567f024ad75 100644
--- a/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Cache/Facades_System.Net.Cache-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj b/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj
index aa3b4a9d9bd..768a126d582 100644
--- a/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.HttpListener/Facades_System.Net.HttpListener-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj b/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj
index f7b2d1e81aa..803df154c3e 100644
--- a/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Mail/Facades_System.Net.Mail-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj b/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj
index eca530fdebd..3eab9350469 100644
--- a/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.NameResolution/Facades_System.Net.NameResolution-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj b/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj
index 07fd052df84..0ade235a5b9 100644
--- a/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.NetworkInformation/Facades_System.Net.NetworkInformation-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj
index 184d968d408..407015beeba 100644
--- a/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Primitives/Facades_System.Net.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj b/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj
index a4dea5a00de..e166c5c165d 100644
--- a/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Requests/Facades_System.Net.Requests-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj b/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj
index 759faff8ace..50a4b713b11 100644
--- a/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Security/Facades_System.Net.Security-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj b/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj
index 9ac5b0cc5b3..26354220d3b 100644
--- a/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.ServicePoint/Facades_System.Net.ServicePoint-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj b/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj
index 4562005c453..cfebce8ca32 100644
--- a/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Sockets/Facades_System.Net.Sockets-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj b/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj
index e76e7c16537..4f3ff315b0c 100644
--- a/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.Utilities/Facades_System.Net.Utilities-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj b/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj
index 2cb4d0bfd6e..d5d1e731099 100644
--- a/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.WebHeaderCollection/Facades_System.Net.WebHeaderCollection-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj b/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj
index 9b6686cd332..3f39649499f 100644
--- a/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.WebSockets.Client/Facades_System.Net.WebSockets.Client-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
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+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj b/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj
index fac0a180763..a0ad52ab922 100644
--- a/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj
+++ b/mcs/class/Facades/System.Net.WebSockets/Facades_System.Net.WebSockets-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
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+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj b/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj
index 44d44976406..2724c08a6c6 100644
--- a/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj
+++ b/mcs/class/Facades/System.ObjectModel/Facades_System.ObjectModel-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj
index 0c9c17e728a..81a9afbf81e 100644
--- a/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Emit.ILGeneration/Facades_System.Reflection.Emit.ILGeneration-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{ACF5E339-FB52-48E0-A859-2CE75756DFE8}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj
index 4705b222f38..fd7b9c397e1 100644
--- a/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Emit.Lightweight/Facades_System.Reflection.Emit.Lightweight-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{03B29131-9D1A-4446-92F2-237F9EF70C5C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj
index 1063e4e2ced..af0da10d141 100644
--- a/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Emit/Facades_System.Reflection.Emit-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5327CF02-204D-45CD-A68D-3D836470E439}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj
index 58547a03e07..2b23a153ef5 100644
--- a/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Extensions/Facades_System.Reflection.Extensions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{B6D0F01A-1585-464E-850A-502EB4BBA8A2}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj
index 191b1a32775..65ba0e8371c 100644
--- a/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.Primitives/Facades_System.Reflection.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{D60D1AB4-D664-4B1F-9724-962A2D205B07}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj b/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj
index 01fb52b1619..791d12a732a 100644
--- a/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection.TypeExtensions/Facades_System.Reflection.TypeExtensions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{C315A617-25A4-447F-AA4F-0E0E7E35F919}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj b/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj
index 02d3b087f26..eb110345c6e 100644
--- a/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj
+++ b/mcs/class/Facades/System.Reflection/Facades_System.Reflection-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{BE1CD06E-F08E-46EE-9DFD-91E1557F4121}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj b/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj
index eb9c2104837..6a593d7f15d 100644
--- a/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj
+++ b/mcs/class/Facades/System.Resources.ReaderWriter/Facades_System.Resources.ReaderWriter-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2D720AF7-7104-46EF-93BC-B8BA133B6BF6}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj b/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj
index 12d69ad137e..5a8f1d514bc 100644
--- a/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj
+++ b/mcs/class/Facades/System.Resources.ResourceManager/Facades_System.Resources.ResourceManager-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{9F980E30-92CE-466A-BCB1-2C2F1E8FC09D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj b/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj
index e1b105b8ce7..22ed800a511 100644
--- a/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.CompilerServices.VisualC/Facades_System.Runtime.CompilerServices.VisualC-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{C1D26AE7-071A-4092-9866-0EE2D09CF342}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj
index ce7e1089bbf..3ce7a1d3dd3 100644
--- a/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Extensions/Facades_System.Runtime.Extensions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{1215B717-BE9D-4D53-AEB9-35522519BC75}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj
index 98cb44511fe..fb2ea70c42a 100644
--- a/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Handles/Facades_System.Runtime.Handles-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{87C01EDD-05AF-4E1A-8EEE-27D7B83689EC}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.InteropServices.RuntimeInformation/Facades_System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj b/mcs/class/Facades/System.Runtime.InteropServices.RuntimeInformation/Facades_System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj
index b6642ce7e73..18f77d2024f 100644
--- a/mcs/class/Facades/System.Runtime.InteropServices.RuntimeInformation/Facades_System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.InteropServices.RuntimeInformation/Facades_System.Runtime.InteropServices.RuntimeInformation-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{71D02788-3AD8-4C43-BDEB-1A3D277496BA}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj b/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj
index ee07679781a..17987e3c4f2 100644
--- a/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.InteropServices.WindowsRuntime/Facades_System.Runtime.InteropServices.WindowsRuntime-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{521A60CF-50DF-4EF1-88B2-418BD39BDEC4}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj b/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj
index c405c184975..86a45cf6195 100644
--- a/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.InteropServices/Facades_System.Runtime.InteropServices-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{71A8C7C9-ED84-44E5-8814-F5FA5DA6EC5A}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj
index b2a7b570b79..81c66e00d80 100644
--- a/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Numerics/Facades_System.Runtime.Numerics-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{AEB47FF6-C50D-4985-A57F-17F71F63694A}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj
index 49cdf197a7c..c450d16dd1c 100644
--- a/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Serialization.Json/Facades_System.Runtime.Serialization.Json-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{88B512E6-3E9D-4F87-A9E4-5F9239848665}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj
index b7972c920a2..66d94578c8f 100644
--- a/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Serialization.Primitives/Facades_System.Runtime.Serialization.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{49BB9015-6989-4BD0-AF82-9184BE637D57}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj b/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj
index 83fe9066784..2e10958a8de 100644
--- a/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime.Serialization.Xml/Facades_System.Runtime.Serialization.Xml-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{C948B3D4-0BEE-4363-B4A7-635A169C8D63}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj b/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj
index 650a456e26f..f515be4f079 100644
--- a/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj
+++ b/mcs/class/Facades/System.Runtime/Facades_System.Runtime-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{CFB32425-69C5-425B-BF9A-66CB3AC52D71}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj b/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj
index 36056b13ea2..0103a2cf5d5 100644
--- a/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.AccessControl/Facades_System.Security.AccessControl-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj b/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj
index afb96de2c54..0bb32b3a3ec 100644
--- a/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Claims/Facades_System.Security.Claims-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj
index e8b8f94c854..d018f87108f 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Algorithms/Facades_System.Security.Cryptography.Algorithms-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj
index 2cf1134a8c5..05e0d309865 100644
--- a/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.DeriveBytes/Facades_System.Security.Cryptography.DeriveBytes-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj
index cb176437a12..2ff55ec01fb 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encoding/Facades_System.Security.Cryptography.Encoding-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj
index 97e09147514..62a5b4a5d43 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption.Aes/Facades_System.Security.Cryptography.Encryption.Aes-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj
index 8fa87165fb0..4f88dc1afec 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDiffieHellman/Facades_System.Security.Cryptography.Encryption.ECDiffieHellman-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj
index cd756908e67..79cc08135f0 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption.ECDsa/Facades_System.Security.Cryptography.Encryption.ECDsa-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj
index 49a17493427..1b964146015 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Encryption/Facades_System.Security.Cryptography.Encryption-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj
index 78460a0b3dc..0d2276e04cd 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Hashing.Algorithms/Facades_System.Security.Cryptography.Hashing.Algorithms-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj
index 27bc36a040b..8030e431897 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Hashing/Facades_System.Security.Cryptography.Hashing-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj
index 9587c7efbaa..351ddecbe39 100644
--- a/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.Primitives/Facades_System.Security.Cryptography.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{62880D99-1C4C-4D38-A8FE-57EF2C9E2150}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj
index 7a9e6bd3638..4c115d1e068 100644
--- a/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.ProtectedData/Facades_System.Security.Cryptography.ProtectedData-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj
index 1a3ce296391..df11f499567 100644
--- a/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.RSA/Facades_System.Security.Cryptography.RSA-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj
index c30809254d7..52bf1b15c83 100644
--- a/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.RandomNumberGenerator/Facades_System.Security.Cryptography.RandomNumberGenerator-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj b/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj
index 9bd0764a207..50ffbf2781f 100644
--- a/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Cryptography.X509Certificates/Facades_System.Security.Cryptography.X509Certificates-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj b/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj
index a532d634c7d..31c7971d560 100644
--- a/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Principal.Windows/Facades_System.Security.Principal.Windows-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj b/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj
index d0a68fbeb32..b12d4ee94e5 100644
--- a/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.Principal/Facades_System.Security.Principal-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj b/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj
index fe27051e21a..785ecc58c2f 100644
--- a/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj
+++ b/mcs/class/Facades/System.Security.SecureString/Facades_System.Security.SecureString-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj
index e3b00882a76..15254d7c903 100644
--- a/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Duplex/Facades_System.ServiceModel.Duplex-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj
index 3a422854b14..905108367bc 100644
--- a/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Http/Facades_System.ServiceModel.Http-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj
index be8116c0ef1..7f167cb1235 100644
--- a/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.NetTcp/Facades_System.ServiceModel.NetTcp-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{0F83D60D-5AAA-425C-BC4E-01CA2018905C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj
index 050d4f109c7..d0c78d06416 100644
--- a/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Primitives/Facades_System.ServiceModel.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{524B10FC-880D-4131-8CAE-027BC3A68B6F}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj b/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj
index ab2adc59efa..126b9db0449 100644
--- a/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceModel.Security/Facades_System.ServiceModel.Security-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{F937A550-0A4A-4A10-9FD9-E8DE7696671F}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj b/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj
index 49b45c859d1..e79a6317a85 100644
--- a/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj
+++ b/mcs/class/Facades/System.ServiceProcess.ServiceController/Facades_System.ServiceProcess.ServiceController-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj b/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj
index bb224b784f4..42e92595086 100644
--- a/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.Encoding.CodePages/Facades_System.Text.Encoding.CodePages-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{DF49AC88-C6F2-43B1-8560-3B74542BD874}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj b/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj
index ebbeac5e1b3..07424aedf05 100644
--- a/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.Encoding.Extensions/Facades_System.Text.Encoding.Extensions-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj b/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj
index 5794d0667e1..2ef5d343716 100644
--- a/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.Encoding/Facades_System.Text.Encoding-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj b/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj
index da65e3f79ad..6ec536aef55 100644
--- a/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj
+++ b/mcs/class/Facades/System.Text.RegularExpressions/Facades_System.Text.RegularExpressions-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj b/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj
index 1d0492f9a52..048a8570564 100644
--- a/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.AccessControl/Facades_System.Threading.AccessControl-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj b/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj
index a9dd68dffd5..6abbd3226c5 100644
--- a/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Overlapped/Facades_System.Threading.Overlapped-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E8BFEFD2-AAB9-45E6-8523-1F6AEB1918A2}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj b/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj
index 84374b1c55c..58f000a535a 100644
--- a/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Tasks.Parallel/Facades_System.Threading.Tasks.Parallel-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{0F8CA9A9-62A4-4829-925E-002F0B93EE79}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj b/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj
index 17c863709d2..fa64a5daf06 100644
--- a/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Tasks/Facades_System.Threading.Tasks-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{F322318E-D053-45C9-AFDF-2AEEE1E0E006}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj b/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj
index 36554ee5e12..6bfe8baef21 100644
--- a/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Thread/Facades_System.Threading.Thread-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{4D9EF694-5260-432D-BA34-503FFBE43B6C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj b/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj
index 2d512f45479..a041ebd251b 100644
--- a/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.ThreadPool/Facades_System.Threading.ThreadPool-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{95B411AA-B13F-4621-B020-7F797E1F39F0}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj b/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj
index 7f3f1a1530d..d0ad984b9ef 100644
--- a/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading.Timer/Facades_System.Threading.Timer-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{30F7C900-122A-42A6-9669-D5606B9105A5}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj b/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj
index 67a1cc4aab6..cbc2567be80 100644
--- a/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj
+++ b/mcs/class/Facades/System.Threading/Facades_System.Threading-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{35258CFB-0308-493D-B2BD-B044EAFD5AD1}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj b/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj
index 59d6ffcbe79..89fb274349e 100644
--- a/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj
+++ b/mcs/class/Facades/System.ValueTuple/Facades_System.ValueTuple-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj b/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj
index a55a827a1ab..1105bd001d7 100644
--- a/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.ReaderWriter/Facades_System.Xml.ReaderWriter-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj b/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj
index d27a4d1e90d..841f127e36c 100644
--- a/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XDocument/Facades_System.Xml.XDocument-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj b/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj
index 2ec12c2ad1a..a159ff64bc5 100644
--- a/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XPath.XDocument/Facades_System.Xml.XPath.XDocument-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj b/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj
index b0d265fcf72..cbb259a06c1 100644
--- a/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XPath/Facades_System.Xml.XPath-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5C3F0B44-E169-4441-91F9-7285048F4946}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj b/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj
index 322ab3d5836..a3fd1c8fd9a 100644
--- a/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XmlDocument/Facades_System.Xml.XmlDocument-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{D7F840DE-EDFD-4DB5-ACDB-9328AB7E6C6C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj b/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj
index 8313c8cc67b..57ab31f45a1 100644
--- a/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.XmlSerializer/Facades_System.Xml.XmlSerializer-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E95FA58F-8086-45FF-8BD3-5A1FAF776709}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj b/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj
index 41fe59f56e4..746e0488312 100644
--- a/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj
+++ b/mcs/class/Facades/System.Xml.Xsl.Primitives/Facades_System.Xml.Xsl.Primitives-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{653C4BDE-F194-4A4F-A1CE-1FF955DE43D6}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj b/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj
index c4a00306639..45e80274411 100644
--- a/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj
+++ b/mcs/class/Facades/netstandard/Facades_netstandard-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{ECE97482-6E06-424A-8E60-46C5B1CCB47C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1616,1699,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj b/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj
index eb7fb38ccbd..c08c22d77d9 100644
--- a/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj
+++ b/mcs/class/I18N/CJK/I18N.CJK-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{4742C0FA-2C03-4598-A3F2-4E7D9CDFF81B}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/I18N/Common/I18N-net_4_x.csproj b/mcs/class/I18N/Common/I18N-net_4_x.csproj
index f34db0baf82..6cec53996cd 100644
--- a/mcs/class/I18N/Common/I18N-net_4_x.csproj
+++ b/mcs/class/I18N/Common/I18N-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E831A310-28EE-4433-B916-FF38A0FCDBE6}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj b/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj
index dfc780c18ce..db14f53e672 100644
--- a/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj
+++ b/mcs/class/I18N/MidEast/I18N.MidEast-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{CF9EC4FE-1FBF-4583-ADE9-D0E6554D4528}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj b/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj
index 54f9226e215..d3f4379a2ac 100644
--- a/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj
+++ b/mcs/class/I18N/Other/I18N.Other-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{990903B9-BEDF-472C-97B8-221F8AA0A731}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj b/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj
index f87ef9d1620..12241648a0c 100644
--- a/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj
+++ b/mcs/class/I18N/Rare/I18N.Rare-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{83227E53-5469-412F-B936-74AD08CDD9D9}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/I18N/West/I18N.West-net_4_x.csproj b/mcs/class/I18N/West/I18N.West-net_4_x.csproj
index 3a394a6eaa5..bca75019139 100644
--- a/mcs/class/I18N/West/I18N.West-net_4_x.csproj
+++ b/mcs/class/I18N/West/I18N.West-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{3516F613-9194-4B95-B7B2-3F9B37A87B30}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj b/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj
index a534852df39..6624d137723 100644
--- a/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj
+++ b/mcs/class/IBM.Data.DB2/IBM.Data.DB2-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{83DC05C9-3C7E-44D9-8D56-5619CF832BC5}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj b/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj
index deb56a65543..ea8b1bd74bd 100644
--- a/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj
+++ b/mcs/class/ICSharpCode.SharpZipLib/ICSharpCode.SharpZipLib-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{4903F98F-B4C9-467A-8FBA-39E7F91D9327}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj b/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj
index ecdf627658d..9533ec3d94e 100644
--- a/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Engine/Microsoft.Build.Engine-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{75DFF196-FA56-48CD-9A1A-CEA3BEC618AB}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj b/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj
index ef67c352b77..a5dd9cad486 100644
--- a/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Framework/Microsoft.Build.Framework-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5E39A911-F4E6-4B4B-B8AC-111BB1DD80C6}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj b/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj
index 36932f8720c..cfd0f45ae1e 100644
--- a/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Tasks/Microsoft.Build.Tasks-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{979FCA08-E170-4BA6-969B-30213135BEA3}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj b/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj
index edc3805fcf3..1b2bad4535f 100644
--- a/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build.Utilities/Microsoft.Build.Utilities-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{8E5728E0-CEAF-431F-963E-EB1DEE15C506}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj b/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj
index ad94614138c..821b23550d2 100644
--- a/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj
+++ b/mcs/class/Microsoft.Build/Microsoft.Build-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{124B6594-F3EC-4FE3-B5A8-2A5CB4D5BC5A}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj b/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj
index ae0297a9288..844eb523da4 100644
--- a/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj
+++ b/mcs/class/Microsoft.CSharp/Microsoft.CSharp-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{DABF9F75-63AD-4991-9D2B-9234E7032B32}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
@@ -170,7 +171,6 @@
     <Compile Include="..\..\..\external\corefx\src\Microsoft.CSharp\src\Microsoft\CSharp\RuntimeBinder\Semantics\Tree\LocalVariable.cs" />
     <Compile Include="..\..\..\external\corefx\src\Microsoft.CSharp\src\Microsoft\CSharp\RuntimeBinder\Semantics\Tree\MemberGroup.cs" />
     <Compile Include="..\..\..\external\corefx\src\Microsoft.CSharp\src\Microsoft\CSharp\RuntimeBinder\Semantics\Tree\MethodInfo.cs" />
-    <Compile Include="..\..\..\external\corefx\src\Microsoft.CSharp\src\Microsoft\CSharp\RuntimeBinder\Semantics\Tree\MethodReference.cs" />
     <Compile Include="..\..\..\external\corefx\src\Microsoft.CSharp\src\Microsoft\CSharp\RuntimeBinder\Semantics\Tree\NamedArgumentSpecification.cs" />
     <Compile Include="..\..\..\external\corefx\src\Microsoft.CSharp\src\Microsoft\CSharp\RuntimeBinder\Semantics\Tree\Property.cs" />
     <Compile Include="..\..\..\external\corefx\src\Microsoft.CSharp\src\Microsoft\CSharp\RuntimeBinder\Semantics\Tree\PropertyInfo.cs" />
diff --git a/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj b/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj
index 29b07b3ae91..61c7ba9f936 100644
--- a/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj
+++ b/mcs/class/Microsoft.VisualC/Microsoft.VisualC-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{ACA2694D-9F07-4AE2-9171-9AB5DD1A8C18}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj b/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj
index 1ee471ea376..fd2e3d52790 100644
--- a/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj
+++ b/mcs/class/Microsoft.Web.Infrastructure/Microsoft.Web.Infrastructure-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{CD409902-9DA0-48A3-B360-C09060168CB5}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj b/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj
index 699440bf3fc..9a7a8c56c6c 100644
--- a/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj
+++ b/mcs/class/Mono.Btls.Interface/Mono.Btls.Interface-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{BF32D586-8FBB-4A2A-A734-AA17CDAB283F}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,1030</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj b/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj
index adb32867c3c..012b5688acc 100644
--- a/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj
+++ b/mcs/class/Mono.C5/Mono.C5-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,169,219,414,1030,3001,3005,3006</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj b/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj
index b7d2587e54f..406d6245062 100644
--- a/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj
+++ b/mcs/class/Mono.CSharp/Mono.CSharp-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{BEFCA993-98B4-48E9-8D68-1ACCB1FA7200}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj b/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj
index faf57690f4b..1ebc6e5edc3 100644
--- a/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj
+++ b/mcs/class/Mono.Cairo/Mono.Cairo-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj b/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj
index c0e7206ad9b..d6b4fb77dda 100644
--- a/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj
+++ b/mcs/class/Mono.Cecil.Mdb/Mono.Cecil.Mdb-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{CF14D34A-F69B-47FB-A99C-D25C77198F30}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj b/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj
index 46099bcf597..edcd825fc1e 100644
--- a/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj
+++ b/mcs/class/Mono.Cecil/Mono.Cecil-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2C0D558F-0B38-4691-967E-A910A1B995C1}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj b/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj
index 846f7869a75..dac4c457a84 100644
--- a/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj
+++ b/mcs/class/Mono.CodeContracts/Mono.CodeContracts-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{9BE8D62B-471D-4538-8287-691B4ECE3209}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj b/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj
index 40691be6e49..7ff19e34a95 100644
--- a/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj
+++ b/mcs/class/Mono.CompilerServices.SymbolWriter/Mono.CompilerServices.SymbolWriter-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{88177C4B-894F-485D-B95A-44199C06BE9F}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj b/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj
index 6ccaf6beb17..7b15c4616be 100644
--- a/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj
+++ b/mcs/class/Mono.Data.Sqlite/Mono.Data.Sqlite-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{371560EA-7BD3-4025-90CB-F1B112403CF2}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj b/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj
index facf9bd018d..06f555f0231 100644
--- a/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj
+++ b/mcs/class/Mono.Data.Tds/Mono.Data.Tds-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj b/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj
index 37889b8b035..5558ba5e16a 100644
--- a/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj
+++ b/mcs/class/Mono.Debugger.Soft/Mono.Debugger.Soft-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj b/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj
index 3c0b0645846..cbed5de32d4 100644
--- a/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj
+++ b/mcs/class/Mono.Http/Mono.Http-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj b/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj
index bd2cc206a9c..37488ceb6a9 100644
--- a/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj
+++ b/mcs/class/Mono.Management/Mono.Management-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Messaging.RabbitMQ/Mono.Messaging.RabbitMQ-net_4_x.csproj b/mcs/class/Mono.Messaging.RabbitMQ/Mono.Messaging.RabbitMQ-net_4_x.csproj
index 49b38c9bfa4..b45a5bae3d3 100644
--- a/mcs/class/Mono.Messaging.RabbitMQ/Mono.Messaging.RabbitMQ-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj b/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj
index 9f678461d37..5701f11fa66 100644
--- a/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj
+++ b/mcs/class/Mono.Messaging/Mono.Messaging-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj b/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj
index 57ed07325a3..9fcd9be1227 100644
--- a/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj
+++ b/mcs/class/Mono.Options/Mono.Options-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj b/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj
index 19905379653..10974eb8c26 100644
--- a/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj
+++ b/mcs/class/Mono.Parallel/Mono.Parallel-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj b/mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj
index 19fd6ed12ac..ab96fd46cd0 100644
--- a/mcs/class/Mono.Posix/Mono.Posix-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,618,612</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Mono.Profiler.Log/Mono.Profiler.Log-net_4_x.csproj b/mcs/class/Mono.Profiler.Log/Mono.Profiler.Log-net_4_x.csproj
index 64d0b98530a..3e8e16f0cea 100644
--- a/mcs/class/Mono.Profiler.Log/Mono.Profiler.Log-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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diff --git a/mcs/class/Mono.Security.Win32/Mono.Security.Win32-net_4_x.csproj b/mcs/class/Mono.Security.Win32/Mono.Security.Win32-net_4_x.csproj
index eecb7af7844..8ae500e1caa 100644
--- a/mcs/class/Mono.Security.Win32/Mono.Security.Win32-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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diff --git a/mcs/class/Mono.Security/Mono.Security-net_4_x.csproj b/mcs/class/Mono.Security/Mono.Security-net_4_x.csproj
index 7a9b42a261f..10c79a93308 100644
--- a/mcs/class/Mono.Security/Mono.Security-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1030,3009</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj b/mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj
index dfa779bded9..cf3089acf91 100644
--- a/mcs/class/Mono.Simd/Mono.Simd-net_4_x.csproj
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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diff --git a/mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj b/mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj
index c06082de92a..3f85b90e4bc 100644
--- a/mcs/class/Mono.Tasklets/Mono.Tasklets-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj b/mcs/class/Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj
index e703853d1e0..5e1b7bc2019 100644
--- a/mcs/class/Mono.WebBrowser/Mono.WebBrowser-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <NoWarn>1699</NoWarn>
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diff --git a/mcs/class/Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj b/mcs/class/Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj
index a2b913f2ac8..fb8d7eb8b8a 100644
--- a/mcs/class/Mono.XBuild.Tasks/Mono.XBuild.Tasks-net_4_x.csproj
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj b/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj
index 294428a63a5..97d937d23cd 100644
--- a/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj
+++ b/mcs/class/Novell.Directory.Ldap/Novell.Directory.Ldap-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,612</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/PEAPI/PEAPI-net_4_x.csproj b/mcs/class/PEAPI/PEAPI-net_4_x.csproj
index be03c4c190a..1092f0ba391 100644
--- a/mcs/class/PEAPI/PEAPI-net_4_x.csproj
+++ b/mcs/class/PEAPI/PEAPI-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,414,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj b/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj
index 8dcf85f974b..c300268196e 100644
--- a/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj
+++ b/mcs/class/RabbitMQ.Client/src/apigen/RabbitMQ.Client.Apigen-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Exe</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj b/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj
index fc55f08b72b..93fc52b3c51 100644
--- a/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj
+++ b/mcs/class/RabbitMQ.Client/src/client/RabbitMQ.Client-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj b/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj
index cf18876f4f1..2a8d0859e53 100644
--- a/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj
+++ b/mcs/class/SMDiagnostics/SMDiagnostics-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj b/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj
index c4c2cf627f5..8c90ff50dac 100644
--- a/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj
+++ b/mcs/class/System.ComponentModel.Composition.4.5/System.ComponentModel.Composition-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,219,414,436</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj b/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj
index a1006040598..0d093ec8a91 100644
--- a/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj
+++ b/mcs/class/System.ComponentModel.DataAnnotations/System.ComponentModel.DataAnnotations-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,414</NoWarn>
+    <LangVersion>latest</LangVersion>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj b/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj
index 5ab112c541f..d61f54c8e06 100644
--- a/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj
+++ b/mcs/class/System.Configuration.Install/System.Configuration.Install-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{B144ACD4-089D-4769-8605-583FBEDB5B7C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj b/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj
index 5f2afcbbc6d..3803d449d33 100644
--- a/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj
+++ b/mcs/class/System.Configuration/System.Configuration-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,618</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.Core/System.Core-net_4_x.csproj b/mcs/class/System.Core/System.Core-net_4_x.csproj
index 0d3ca818c39..0157d383133 100644
--- a/mcs/class/System.Core/System.Core-net_4_x.csproj
+++ b/mcs/class/System.Core/System.Core-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{359142A1-D80F-401E-AA64-7167C9317649}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,436</NoWarn>
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diff --git a/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj b/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj
index 4a21e89df24..e152bc19dae 100644
--- a/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj
+++ b/mcs/class/System.Data.DataSetExtensions/System.Data.DataSetExtensions-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,436</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj b/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj
index 677eca3aeac..5f8ab881175 100644
--- a/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj
+++ b/mcs/class/System.Data.Entity/System.Data.Entity-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Data.Linq/System.Data.Linq-net_4_x.csproj b/mcs/class/System.Data.Linq/System.Data.Linq-net_4_x.csproj
index 872c8d77e77..91f54123bbe 100644
--- a/mcs/class/System.Data.Linq/System.Data.Linq-net_4_x.csproj
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@@ -9,6 +9,7 @@
     <ProjectGuid>{E6EE9E9A-42BA-4202-8813-FCF40E9061BF}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj b/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj
index 003c82ac85c..3ae9306759e 100644
--- a/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj
+++ b/mcs/class/System.Data.OracleClient/System.Data.OracleClient-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{0029417C-ED54-4162-8D8C-D935C760D89D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj b/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj
index 4764ab684f0..9a31fe8e9c8 100644
--- a/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj
+++ b/mcs/class/System.Data.Services.Client/System.Data.Services.Client-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Data.Services/System.Data.Services-net_4_x.csproj b/mcs/class/System.Data.Services/System.Data.Services-net_4_x.csproj
index 5b2af612e8a..88357767b02 100644
--- a/mcs/class/System.Data.Services/System.Data.Services-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Data/System.Data-net_4_x.csproj b/mcs/class/System.Data/System.Data-net_4_x.csproj
index acd62fcbbb3..289df1bdb29 100644
--- a/mcs/class/System.Data/System.Data-net_4_x.csproj
+++ b/mcs/class/System.Data/System.Data-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,219,414,649,619</NoWarn>
+    <LangVersion>latest</LangVersion>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj b/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj
index 2b4ff5a7bb6..b21feb0f310 100644
--- a/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj
+++ b/mcs/class/System.Deployment/System.Deployment-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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diff --git a/mcs/class/System.Design/System.Design-net_4_x.csproj b/mcs/class/System.Design/System.Design-net_4_x.csproj
index 6421cc7663c..d4e4aab8ae0 100644
--- a/mcs/class/System.Design/System.Design-net_4_x.csproj
+++ b/mcs/class/System.Design/System.Design-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,436,612,618,649,67,672</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj b/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj
index 04f030a734d..4294869c185 100644
--- a/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj
+++ b/mcs/class/System.Design/System.Design-plaindesign-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <NoWarn>1699,436,612,618,649,67,672</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj b/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj
index 998f764aa23..7719198d684 100644
--- a/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj
+++ b/mcs/class/System.DirectoryServices.Protocols/System.DirectoryServices.Protocols-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
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diff --git a/mcs/class/System.DirectoryServices/System.DirectoryServices-net_4_x.csproj b/mcs/class/System.DirectoryServices/System.DirectoryServices-net_4_x.csproj
index 72768debbe6..7d1e75d2b58 100644
--- a/mcs/class/System.DirectoryServices/System.DirectoryServices-net_4_x.csproj
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@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj b/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj
index e99794a211f..b4737806c33 100644
--- a/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj
+++ b/mcs/class/System.Drawing.Design/System.Drawing.Design-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <NoWarn>1699</NoWarn>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj b/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj
index 19ebc40176a..b9682e0a025 100644
--- a/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj
+++ b/mcs/class/System.Drawing/System.Drawing-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj b/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj
index 7b164e13187..a93ded3023d 100644
--- a/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj
+++ b/mcs/class/System.Dynamic/System.Dynamic-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,414,169</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj b/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj
index 4bb39d0aae7..5e577a9569c 100644
--- a/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj
+++ b/mcs/class/System.EnterpriseServices/System.EnterpriseServices-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,168,162</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj b/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj
index 5c0d8fc6060..7f4622822f6 100644
--- a/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj
+++ b/mcs/class/System.IO.Compression.FileSystem/System.IO.Compression.FileSystem-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{9E61FF2E-493E-4CA0-BBDA-2EF96A4CB058}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj b/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj
index 7fc2b92eb90..2ae09a8c009 100644
--- a/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj
+++ b/mcs/class/System.IO.Compression/System.IO.Compression-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj b/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj
index b64955547ab..2fcca27ed43 100644
--- a/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj
+++ b/mcs/class/System.IdentityModel.Selectors/System.IdentityModel.Selectors-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{BBA32980-B28C-476D-AEB0-892F1B1DFB5E}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj b/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj
index af6ccf8ab47..feba613635a 100644
--- a/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj
+++ b/mcs/class/System.IdentityModel/System.IdentityModel-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj b/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj
index d249b19fd46..4201b7a10a3 100644
--- a/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj
+++ b/mcs/class/System.Json.Microsoft/System.Json.Microsoft-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Json/System.Json-net_4_x.csproj b/mcs/class/System.Json/System.Json-net_4_x.csproj
index 7670a0c6f2a..4b43d741be7 100644
--- a/mcs/class/System.Json/System.Json-net_4_x.csproj
+++ b/mcs/class/System.Json/System.Json-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Management/System.Management-net_4_x.csproj b/mcs/class/System.Management/System.Management-net_4_x.csproj
index cc88b18e25b..cdf9f654a27 100644
--- a/mcs/class/System.Management/System.Management-net_4_x.csproj
+++ b/mcs/class/System.Management/System.Management-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{A81C8BB6-5799-49BC-849A-CB422D3F8DB9}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj b/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj
index f61c3950175..11dbad92a4f 100644
--- a/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj
+++ b/mcs/class/System.Messaging/System.Messaging-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj b/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj
index 9f79472b2e3..1cbbae7ee3f 100644
--- a/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj
+++ b/mcs/class/System.Net.Http.Formatting/System.Net.Http.Formatting-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5883D056-B748-4D13-A7E3-2D2756CDC6BC}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj b/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj
index f24cb4e1336..84d337fe81f 100644
--- a/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj
+++ b/mcs/class/System.Net.Http.WebRequest/System.Net.Http.WebRequest-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj b/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj
index 9fc881ffd2e..cf46fcee85a 100644
--- a/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj
+++ b/mcs/class/System.Net.Http/System.Net.Http-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Net/System.Net-net_4_x.csproj b/mcs/class/System.Net/System.Net-net_4_x.csproj
index 676add57b65..4ea83c4cdc7 100644
--- a/mcs/class/System.Net/System.Net-net_4_x.csproj
+++ b/mcs/class/System.Net/System.Net-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699,1720</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj b/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj
index cf78a442bdb..c27492aaf3e 100644
--- a/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj
+++ b/mcs/class/System.Numerics.Vectors/System.Numerics.Vectors-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj b/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj
index 33f0f821f84..bf10bd3b16d 100644
--- a/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj
+++ b/mcs/class/System.Numerics/System.Numerics-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{BD2FFDDC-BD89-4041-82F5-A696C941C7BE}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj b/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj
index 7e1a30f7a23..27b112c2c01 100644
--- a/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Core/System.Reactive.Core-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{52F7F1BD-9D67-494E-A53A-C291FF5424B4}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
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diff --git a/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj b/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj
index f1a770ce14a..18d803f2c2a 100644
--- a/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Debugger/System.Reactive.Debugger-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{8EB36024-5DB5-4854-8425-8D95A8059F2D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
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diff --git a/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj b/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj
index a6fff28b73e..30f4908f8f7 100644
--- a/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Experimental/System.Reactive.Experimental-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj b/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj
index e8079c10984..fa93f640c49 100644
--- a/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Interfaces/System.Reactive.Interfaces-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj b/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj
index 9da3834794a..8955c302dd2 100644
--- a/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Linq/System.Reactive.Linq-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
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diff --git a/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj b/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj
index 0d9aeb111f9..633727ff483 100644
--- a/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Observable.Aliases/System.Reactive.Observable.Aliases-net_4_x.csproj
@@ -9,6 +9,7 @@
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     <NoWarn>1699</NoWarn>
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     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj b/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj
index ebbf6a33052..d46fc7e310c 100644
--- a/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj
+++ b/mcs/class/System.Reactive.PlatformServices/System.Reactive.PlatformServices-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{00CF93F7-B48C-4AF7-B8D5-58DFFAD22845}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj b/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj
index e0415dc170a..92b8b9666f3 100644
--- a/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Providers/System.Reactive.Providers-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{22187CB5-7451-45B4-B21B-337D956FF05D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj b/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj
index 31baf38541f..6d297574383 100644
--- a/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Runtime.Remoting/System.Reactive.Runtime.Remoting-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{7675D4A6-F017-4D20-BFE3-295B86F166CD}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj b/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj
index f6f8490390e..40d70d35adb 100644
--- a/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Windows.Forms/System.Reactive.Windows.Forms-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{9DA5F2F9-AF47-4D48-BA58-2FAFD12538C7}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj b/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj
index 88b1b2c2ec9..a13fa27ba2c 100644
--- a/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj
+++ b/mcs/class/System.Reactive.Windows.Threading/System.Reactive.Windows.Threading-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{52C2AE83-A947-42CC-ADEF-9F54042D85D5}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj b/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj
index 8d5d859ec27..0b916a713e2 100644
--- a/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj
+++ b/mcs/class/System.Reflection.Context/System.Reflection.Context-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{50A4818C-4BD7-49DB-AD2C-FF3FB0A9D392}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj b/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj
index ea284aa57ff..c994e567b5d 100644
--- a/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Caching/System.Runtime.Caching-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2FE2D8C6-B7B8-4067-A2C0-9D1DEA020FD8}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,414</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj b/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj
index 2f7f0e9fd94..62b49150313 100644
--- a/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj
+++ b/mcs/class/System.Runtime.DurableInstancing/System.Runtime.DurableInstancing-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{67822258-3D1E-449F-ACDD-BE1918B44458}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj b/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj
index 9bc8cb571d0..a141bbdbe7c 100644
--- a/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Remoting/System.Runtime.Remoting-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{F19F77AE-1A81-4676-BAB8-6C1DA243A961}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj b/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj
index 26a5cce0de4..ac73b4fee38 100644
--- a/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Serialization.Formatters.Soap/System.Runtime.Serialization.Formatters.Soap-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{A157AD69-59D4-49DE-94B3-DB883B2BEAA5}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj b/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj
index 78b388c5f2e..4ae6f4c5b0d 100644
--- a/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj
+++ b/mcs/class/System.Runtime.Serialization/System.Runtime.Serialization-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{D845AD9D-3CCB-49CB-9543-028678E94938}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,168,169,219,414,618,1634</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Security/System.Security-net_4_x.csproj b/mcs/class/System.Security/System.Security-net_4_x.csproj
index aad71444d75..bf7333e31d7 100644
--- a/mcs/class/System.Security/System.Security-net_4_x.csproj
+++ b/mcs/class/System.Security/System.Security-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{3ED36717-A9D1-4289-8949-9B7F39766DEB}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,414,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj b/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj
index e26830a4f6a..af0a40ee257 100644
--- a/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Activation/System.ServiceModel.Activation-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{7A23227C-591B-4F80-9D62-4D0271073D82}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj
index ad3a3b25912..f1f6c319e72 100644
--- a/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Discovery/System.ServiceModel.Discovery-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2D03C898-0B45-4CAA-A333-B2463B81C37B}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj b/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj
index 398bad350c8..7344a6b1134 100644
--- a/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Internals/System.ServiceModel.Internals-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{5769B536-7E8E-4C2A-8671-6B256D0F620B}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj b/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj
index fc1be9b6732..63a92c15180 100644
--- a/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Routing/System.ServiceModel.Routing-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{55BBC4F8-6DA2-4B3D-8714-F45A255F8BCC}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj b/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj
index 1b4dc381ec4..fda53c7b043 100644
--- a/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel.Web/System.ServiceModel.Web-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{54F4FA23-5AF3-4312-9294-3DB109F644CC}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj b/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj
index 6b31dd5a70b..fd74c8aa7ad 100644
--- a/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel/System.ServiceModel-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{FE596C31-BDA2-4850-8F79-F8F4DF70F44A}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,414,169,67,3005,436,219,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj b/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj
index 1c8f339bf35..26646da3c6c 100644
--- a/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj
+++ b/mcs/class/System.ServiceModel/System.ServiceModel-plainservice-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{88C258E1-F0AF-47DA-96C8-7FA6421067CD}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,414,169,67,3005,436,219,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj b/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj
index aa2e532cdb8..b63e69e5181 100644
--- a/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj
+++ b/mcs/class/System.ServiceProcess/System.ServiceProcess-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{CF24A609-AEF3-4E7A-95FC-C7A3CEAA7CC3}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj b/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj
index de5a040ad52..cdb4d74de53 100644
--- a/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj
+++ b/mcs/class/System.Threading.Tasks.Dataflow/System.Threading.Tasks.Dataflow-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{70A422C5-17AF-48EE-8DD8-CF88D482606C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj b/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj
index cb281677b77..2f520209f00 100644
--- a/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj
+++ b/mcs/class/System.Transactions/System.Transactions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{3821C69F-220D-4231-992C-0FE05311A005}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj b/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj
index 9a8e515faf1..c23c9ee724e 100644
--- a/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj
+++ b/mcs/class/System.Web.Abstractions/System.Web.Abstractions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{79D6E70D-8FD8-4EAA-9E81-B32B5C2815FB}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj b/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj
index 84b0e2d6bf2..3e2d8b7ac4d 100644
--- a/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj
+++ b/mcs/class/System.Web.ApplicationServices/System.Web.ApplicationServices-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{928432BE-3518-4103-97F6-48B9658588A6}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj b/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj
index b2ae64f9c5d..2ab10d19f21 100644
--- a/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj
+++ b/mcs/class/System.Web.DynamicData/System.Web.DynamicData-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E5E3F230-57CA-4685-B1C4-A164F0876755}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj b/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj
index c49d4291f19..c4ac867e95f 100644
--- a/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj
+++ b/mcs/class/System.Web.Extensions.Design/System.Web.Extensions.Design-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{288BFBFF-D78E-4EB3-ABF4-A5BCBB1BD9C9}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj b/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj
index 403af8f4fa6..463d1fdfc51 100644
--- a/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj
+++ b/mcs/class/System.Web.Extensions/System.Web.Extensions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{EE582CE1-A692-47AC-B838-3A78955898BE}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,436</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj b/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj
index fd014453b10..a78ae6df50a 100644
--- a/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj
+++ b/mcs/class/System.Web.Http.SelfHost/System.Web.Http.SelfHost-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{0E705D1C-A4C4-41C2-832D-C812F3D4CB3C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj b/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj
index 022b334bb22..a908b9516af 100644
--- a/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj
+++ b/mcs/class/System.Web.Http.WebHost/System.Web.Http.WebHost-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2AF7E697-07BA-439E-89BF-076AEE4AE04C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj b/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj
index 264f4e2a4ee..07c385e518f 100644
--- a/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj
+++ b/mcs/class/System.Web.Http/System.Web.Http-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{6DDAE502-A602-410C-B182-C18D5100DDB0}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj b/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj
index ac2f935279c..89cbab5709e 100644
--- a/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj
+++ b/mcs/class/System.Web.Mobile/System.Web.Mobile-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E676BC22-5B81-4518-8243-3946BB57D665}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj b/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj
index 38290c8ed9d..79f41ef4b81 100644
--- a/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj
+++ b/mcs/class/System.Web.Mvc3/System.Web.Mvc3-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{14D0E9AA-AF30-4E40-983F-8BE66423E6AF}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj b/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj
index 1f85a9bf6e2..411d6390025 100644
--- a/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj
+++ b/mcs/class/System.Web.Razor/System.Web.Razor-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{11928A85-4C26-4258-AC86-2AFB0A69DED2}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj b/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj
index 7b6c517a385..947f3976e2a 100644
--- a/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj
+++ b/mcs/class/System.Web.RegularExpressions/System.Web.RegularExpressions-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{9B52B7BD-1E14-4300-BEC5-241513810554}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj b/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj
index c48f03f9a09..7aa9d883520 100644
--- a/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj
+++ b/mcs/class/System.Web.Routing/System.Web.Routing-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{EBD67AE3-F249-4768-A143-6B2F9E56BC39}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj b/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj
index bb0a2395a8e..7f92c6fa546 100644
--- a/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj
+++ b/mcs/class/System.Web.Services/System.Web.Services-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E43ADBA7-5DB9-466B-90C6-FFFDA520848D}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,168,612,618,649</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj b/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj
index 99ec1af6a95..a8bd0e65ac1 100644
--- a/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj
+++ b/mcs/class/System.Web.WebPages.Deployment/System.Web.WebPages.Deployment-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{12C344E9-64D1-4F94-BAB6-1231B863EE6C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj b/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj
index e7375fb58ad..9e01ddd82cb 100644
--- a/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj
+++ b/mcs/class/System.Web.WebPages.Razor/System.Web.WebPages.Razor-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{55F0BCD6-4B0B-408C-BE98-4BFF82157048}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj b/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj
index 959f40d093c..db17c591015 100644
--- a/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj
+++ b/mcs/class/System.Web.WebPages/System.Web.WebPages-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{D4EAC129-92AB-432C-941D-4B8481097060}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web/System.Web-net_4_x.csproj b/mcs/class/System.Web/System.Web-net_4_x.csproj
index dce363b00d9..224b4a6d10e 100644
--- a/mcs/class/System.Web/System.Web-net_4_x.csproj
+++ b/mcs/class/System.Web/System.Web-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{9DB806CB-B828-49B7-BAE2-2E52402CB4DC}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,612,618,436,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj b/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj
index 62300b2a636..f54cb24bd75 100644
--- a/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj
+++ b/mcs/class/System.Web/System.Web-plainweb-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{DE51B021-D51C-4F26-99EE-B0729D97631E}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,612,618,436,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj b/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj
index 650b035dda8..ed90a7c78a6 100644
--- a/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj
+++ b/mcs/class/System.Windows.Forms.DataVisualization/System.Windows.Forms.DataVisualization-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{C6A36476-0B2B-45BA-B4DD-05C39E63F3BE}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,67</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj b/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj
index 48e2bcc9db4..70db7a33ea1 100644
--- a/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj
+++ b/mcs/class/System.Windows.Forms/System.Windows.Forms-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{108227C7-8ED9-4483-949D-07BF0DA1A201}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,618,612,809</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Windows/System.Windows-net_4_x.csproj b/mcs/class/System.Windows/System.Windows-net_4_x.csproj
index 1a7d7391403..58d6b75c843 100644
--- a/mcs/class/System.Windows/System.Windows-net_4_x.csproj
+++ b/mcs/class/System.Windows/System.Windows-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{3F6EB6D4-602E-43C2-A3E1-4AD98E8C86EE}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj b/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj
index b8277897a74..d60a56f6294 100644
--- a/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj
+++ b/mcs/class/System.Workflow.Activities/System.Workflow.Activities-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{29FCE500-BC83-4BF0-AED0-4E96932182F7}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj b/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj
index 605e03dbaa4..b8037736d5b 100644
--- a/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj
+++ b/mcs/class/System.Workflow.ComponentModel/System.Workflow.ComponentModel-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{3424BA74-B0AE-4C5E-A2C6-6FF86369D510}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj b/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj
index bc133eb5897..ad04e59187f 100644
--- a/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj
+++ b/mcs/class/System.Workflow.Runtime/System.Workflow.Runtime-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{E4180397-83B3-4F7B-9878-6891698F7C52}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj b/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj
index 956aab852f8..d1fc356edf3 100644
--- a/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj
+++ b/mcs/class/System.XML/System.Xml-bare-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{A5216031-11A3-44DD-B2FF-A14AE63BD0C3}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,219,414,649,1717</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.XML/System.Xml-net_4_x.csproj b/mcs/class/System.XML/System.Xml-net_4_x.csproj
index f9bc301cb07..27d5da1b333 100644
--- a/mcs/class/System.XML/System.Xml-net_4_x.csproj
+++ b/mcs/class/System.XML/System.Xml-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{87FD2F0F-5222-4AE6-BD63-2D4975E11E5B}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,219,414,649,1717</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj b/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj
index 42f562bf2de..5f3d2e3fa6e 100644
--- a/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj
+++ b/mcs/class/System.Xaml/System.Xaml-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{4E79FA59-8344-4053-8E3B-B9619BA26513}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj b/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj
index b9b94858ba6..844f55fef00 100644
--- a/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj
+++ b/mcs/class/System.Xml.Linq/System.Xml.Linq-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{526286D5-38D9-4579-B001-471440D57752}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj b/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj
index cdf311bffad..9e703e384cf 100644
--- a/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj
+++ b/mcs/class/System.Xml.Serialization/System.Xml.Serialization-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2210873E-99FC-48A2-A261-D650BAE33A1C}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/System/System-bare-net_4_x.csproj b/mcs/class/System/System-bare-net_4_x.csproj
index 4e86cf0e7ca..aad52c2a0aa 100644
--- a/mcs/class/System/System-bare-net_4_x.csproj
+++ b/mcs/class/System/System-bare-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{483DB7F6-9145-4AE2-B9B2-2B5EE6FDEFB4}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,436</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
@@ -1350,6 +1351,11 @@
       <Project>{2CA6026B-2DC8-4C4C-A12C-1E8234049DB7}</Project>
       <Name>corlib-net_4_x</Name>
     </ProjectReference>
+    <Reference Include="./../../../external/api-snapshot/profiles/net_4_x/System.Net.Http.dll">
+      <SpecificVersion>False</SpecificVersion>
+      <HintPath>./../../../external/api-snapshot/profiles/net_4_x/System.Net.Http.dll</HintPath>
+      <Private>False</Private>
+    </Reference>
   </ItemGroup>
   <ItemGroup>
     <Folder Include="Properties\" />
diff --git a/mcs/class/System/System-net_4_x.csproj b/mcs/class/System/System-net_4_x.csproj
index 01ad4190ddd..0a0368cb61b 100644
--- a/mcs/class/System/System-net_4_x.csproj
+++ b/mcs/class/System/System-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{2762E921-91A8-4C87-91E9-BA628013F753}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,436</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
@@ -1350,6 +1351,11 @@
       <Project>{2CA6026B-2DC8-4C4C-A12C-1E8234049DB7}</Project>
       <Name>corlib-net_4_x</Name>
     </ProjectReference>
+    <Reference Include="./../../../external/api-snapshot/profiles/net_4_x/System.Net.Http.dll">
+      <SpecificVersion>False</SpecificVersion>
+      <HintPath>./../../../external/api-snapshot/profiles/net_4_x/System.Net.Http.dll</HintPath>
+      <Private>False</Private>
+    </Reference>
     <ProjectReference Include="../System.XML/System.Xml-net_4_x.csproj">
       <Project>{87FD2F0F-5222-4AE6-BD63-2D4975E11E5B}</Project>
       <Name>System.Xml-net_4_x</Name>
diff --git a/mcs/class/System/System-secxml-net_4_x.csproj b/mcs/class/System/System-secxml-net_4_x.csproj
index c01676c5ad5..0b4a213a3e0 100644
--- a/mcs/class/System/System-secxml-net_4_x.csproj
+++ b/mcs/class/System/System-secxml-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{19954F80-065E-4D46-8FEF-62BA4D6CFDAD}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,436</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
@@ -1350,6 +1351,11 @@
       <Project>{2CA6026B-2DC8-4C4C-A12C-1E8234049DB7}</Project>
       <Name>corlib-net_4_x</Name>
     </ProjectReference>
+    <Reference Include="./../../../external/api-snapshot/profiles/net_4_x/System.Net.Http.dll">
+      <SpecificVersion>False</SpecificVersion>
+      <HintPath>./../../../external/api-snapshot/profiles/net_4_x/System.Net.Http.dll</HintPath>
+      <Private>False</Private>
+    </Reference>
     <ProjectReference Include="../System.XML/System.Xml-bare-net_4_x.csproj">
       <Project>{A5216031-11A3-44DD-B2FF-A14AE63BD0C3}</Project>
       <Name>System.Xml-bare-net_4_x</Name>
diff --git a/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj b/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj
index 7d58a25bcbd..500c8746f5e 100644
--- a/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj
+++ b/mcs/class/SystemWebTestShim/SystemWebTestShim-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{F0A0BBA8-FFB1-4278-B4EF-84BCEAF69133}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj b/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj
index 51aebaae99d..44bdd385ac5 100644
--- a/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj
+++ b/mcs/class/WebMatrix.Data/WebMatrix.Data-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{25552E1C-6EE1-4D73-A309-A1ED7FA26E94}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj b/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj
index e672ffb286e..d5d89df4ad9 100644
--- a/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj
+++ b/mcs/class/WindowsBase/WindowsBase-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{A8F39368-ECD9-41A5-A562-CC7C82B3CC86}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699,67,618</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/corlib/corlib-net_4_x.csproj b/mcs/class/corlib/corlib-net_4_x.csproj
index 25dc0a70c64..943872765cf 100644
--- a/mcs/class/corlib/corlib-net_4_x.csproj
+++ b/mcs/class/corlib/corlib-net_4_x.csproj
@@ -8,7 +8,8 @@
     <SchemaVersion>2.0</SchemaVersion>
     <ProjectGuid>{2CA6026B-2DC8-4C4C-A12C-1E8234049DB7}</ProjectGuid>
     <OutputType>Library</OutputType>
-    <NoWarn>612,618,1635,1699</NoWarn>
+    <NoWarn>612,618,3001,3003,1635,1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
@@ -30,7 +31,7 @@
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
     <DebugType>full</DebugType>
-    <NoWarn>612,618,1635,1699</NoWarn>
+    <NoWarn>612,618,3001,3003,1635,1699</NoWarn>
     <Optimize>false</Optimize>
     <DefineConstants>TRACE;INSIDE_CORLIB;MONO_CULTURE_DATA;LIBC;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ENCODINGNLS;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ENCODINGNLS;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;MONO_FEATURE_CONSOLE;MONO_FEATURE_APPLETLS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
@@ -38,7 +39,7 @@
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DebugType>pdbonly</DebugType>
-    <NoWarn>612,618,1635,1699</NoWarn>
+    <NoWarn>612,618,3001,3003,1635,1699</NoWarn>
     <Optimize>true</Optimize>
     <DefineConstants>INSIDE_CORLIB;MONO_CULTURE_DATA;LIBC;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ENCODINGNLS;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;NET_4_0;NET_4_5;NET_4_6;MONO;WIN_PLATFORM;MULTIPLEX_OS;FEATURE_PAL;GENERICS_WORK;FEATURE_LIST_PREDICATES;FEATURE_SERIALIZATION;FEATURE_ENCODINGNLS;FEATURE_ASCII;FEATURE_LATIN1;FEATURE_UTF7;FEATURE_UTF32;MONO_HYBRID_ENCODING_SUPPORT;FEATURE_ASYNC_IO;NEW_EXPERIMENTAL_ASYNC_IO;FEATURE_UTF32;FEATURE_EXCEPTIONDISPATCHINFO;FEATURE_CORRUPTING_EXCEPTIONS;FEATURE_EXCEPTION_NOTIFICATIONS;FEATURE_STRONGNAME_MIGRATION;FEATURE_USE_LCID;FEATURE_FUSION;FEATURE_CRYPTO;FEATURE_X509_SECURESTRINGS;FEATURE_SYNCHRONIZATIONCONTEXT;FEATURE_SYNCHRONIZATIONCONTEXT_WAIT;HAS_CORLIB_CONTRACTS;FEATURE_MACL;FEATURE_REMOTING;MONO_COM;FEATURE_COMINTEROP;FEATURE_ROLE_BASED_SECURITY;MONO_FEATURE_THREAD_ABORT;MONO_FEATURE_THREAD_SUSPEND_RESUME;MONO_FEATURE_MULTIPLE_APPDOMAINS;MONO_FEATURE_CONSOLE;MONO_FEATURE_APPLETLS</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
@@ -62,7 +63,13 @@
     <Compile Include="..\..\..\external\corefx\src\System.Collections.Concurrent\src\System\Collections\Concurrent\Partitioner.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Collections.Concurrent\src\System\Collections\Concurrent\PartitionerStatic.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Collections\src\System\Collections\Generic\CollectionExtensions.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\Buffers\IRetainable.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\Buffers\MemoryHandle.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\Buffers\OwnedMemory.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\Memory.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\MemoryDebugView.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\Pinnable.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\ReadOnlyMemory.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\ReadOnlySpan.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\Span.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Memory\src\System\SpanDebugView.cs" />
@@ -73,6 +80,11 @@
     <Compile Include="..\..\..\external\corefx\src\System.Runtime.InteropServices.RuntimeInformation\src\System\Runtime\InteropServices\RuntimeInformation\OSPlatform.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Security.Cryptography.X509Certificates\src\System\Security\Cryptography\X509Certificates\X509ContentType.cs" />
     <Compile Include="..\..\..\external\corefx\src\System.Security.Cryptography.X509Certificates\src\System\Security\Cryptography\X509Certificates\X509KeyStorageFlags.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Threading.Tasks.Extensions\src\System\Runtime\CompilerServices\AsyncMethodBuilderAttribute.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Threading.Tasks.Extensions\src\System\Runtime\CompilerServices\AsyncValueTaskMethodBuilder.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Threading.Tasks.Extensions\src\System\Runtime\CompilerServices\ConfiguredValueTaskAwaitable.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Threading.Tasks.Extensions\src\System\Runtime\CompilerServices\ValueTaskAwaiter.cs" />
+    <Compile Include="..\..\..\external\corefx\src\System.Threading.Tasks.Extensions\src\System\Threading\Tasks\ValueTask.cs" />
     <Compile Include="..\..\..\external\corert\src\Common\src\Interop\Unix\Interop.Libraries.cs" />
     <Compile Include="..\..\..\external\corert\src\Common\src\Interop\Unix\System.Private.CoreLib.Native\Interop.MemAllocFree.cs" />
     <Compile Include="..\..\..\external\corert\src\Common\src\Interop\Windows\Interop.Libraries.cs" />
diff --git a/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj b/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj
index 133c4965191..026a270817d 100644
--- a/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj
+++ b/mcs/class/legacy/Mono.Cecil/legacy_Mono.Cecil-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{CF1339E8-584B-4B3D-9A93-6F4AFDAFEE66}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>1699</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
diff --git a/mcs/class/monodoc/monodoc-net_4_x.csproj b/mcs/class/monodoc/monodoc-net_4_x.csproj
index ec63cc31b68..6527ca956b9 100644
--- a/mcs/class/monodoc/monodoc-net_4_x.csproj
+++ b/mcs/class/monodoc/monodoc-net_4_x.csproj
@@ -9,6 +9,7 @@
     <ProjectGuid>{0248869F-8D3B-4AB2-B976-B2A9AF1319A9}</ProjectGuid>
     <OutputType>Library</OutputType>
     <NoWarn>618,612,672,809,414,649,1699,169,164,162,168,219,618,612</NoWarn>
+    <LangVersion>latest</LangVersion>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Windows_NT'">win32</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix' and $([System.IO.File]::Exists('/usr/lib/libc.dylib'))">darwin</HostPlatform>
     <HostPlatform Condition=" '$(HostPlatform)' == '' and '$(OS)' == 'Unix'">linux</HostPlatform>
-- 
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