[2018-06] [corlib] Bring back String.Concat with __arglist (#10458)

Backport of #10452.
Fixes #9996
Tested repro project from the link on a local PostgresSQL server and EntityFramework packages.

See https://github.com/aspnet/EntityFramework6/blob/master/src/EntityFramework/Core/Objects/ELinq/MethodCallTranslator.cs#L1482-L1497

2 files changed, 62 insertions, 0 deletions

diff --git a/mcs/class/corlib/ReferenceSources/String.cs b/mcs/class/corlib/ReferenceSources/String.cs
index 6d8866a058a..f194b7c0f83 100644
--- a/mcs/class/corlib/ReferenceSources/String.cs
+++ b/mcs/class/corlib/ReferenceSources/String.cs
@@ -86,6 +86,13 @@ namespace System
 			return -1;
 		}
 
+		[CLSCompliant(false)] 
+		public static String Concat(Object arg0, Object arg1, Object arg2, Object arg3, __arglist) 
+		{
+			// Added to maintain backward compatibility, see https://github.com/mono/mono/issues/9996
+			throw new PlatformNotSupportedException();
+		}
+
 		internal unsafe int IndexOfUncheckedIgnoreCase (string value, int startIndex, int count)
 		{
 			int valueLen = value.Length;
diff --git a/mcs/class/corlib/Test/System.Reflection/MethodInfoTest.cs b/mcs/class/corlib/Test/System.Reflection/MethodInfoTest.cs
index c68116ea0ee..ef6b571451c 100644
--- a/mcs/class/corlib/Test/System.Reflection/MethodInfoTest.cs
+++ b/mcs/class/corlib/Test/System.Reflection/MethodInfoTest.cs
@@ -31,6 +31,7 @@
 
 using NUnit.Framework;
 using System;
+using System.Linq;
 using System.Threading;
 using System.Reflection;
 #if !MONOTOUCH && !FULL_AOT_RUNTIME
@@ -890,6 +891,60 @@ namespace MonoTests.System.Reflection
 			}
 		}
 
+		static void EnsureMethodExists (Type type, string name, params Type[] parameterTypes)
+		{
+			var method = type.GetTypeInfo ().GetDeclaredMethods (name)
+				.SingleOrDefault (m => m.GetParameters ().Select (p => p.ParameterType).SequenceEqual (parameterTypes));
+			Assert.IsNotNull (method, $"{type}.{name}");
+		}
+
+		public void EnsureEntityFrameworkMethodsExist ()
+		{
+			// EntityFramework6 relies on the following methods
+			// see https://github.com/aspnet/EntityFramework6/blob/master/src/EntityFramework/Core/Objects/ELinq/MethodCallTranslator.cs#L846
+			// also https://github.com/mono/mono/pull/10452
+			EnsureMethodExists (typeof (Math), "Ceiling", typeof (decimal));
+			EnsureMethodExists (typeof (Math), "Ceiling", typeof (double));
+			EnsureMethodExists (typeof (Math), "Floor", typeof (decimal));
+			EnsureMethodExists (typeof (Math), "Floor", typeof (double));
+			EnsureMethodExists (typeof (Math), "Round", typeof (decimal));
+			EnsureMethodExists (typeof (Math), "Round", typeof (double));
+			EnsureMethodExists (typeof (Math), "Round", typeof (decimal), typeof (int));
+			EnsureMethodExists (typeof (Math), "Round", typeof (double), typeof (int));
+			EnsureMethodExists (typeof (Decimal), "Floor", typeof (decimal));
+			EnsureMethodExists (typeof (Decimal), "Ceiling", typeof (decimal));
+			EnsureMethodExists (typeof (Decimal), "Round", typeof (decimal));
+			EnsureMethodExists (typeof (Decimal), "Round", typeof (decimal), typeof (int));
+			EnsureMethodExists (typeof (String), "Replace", typeof (String), typeof (String));
+			EnsureMethodExists (typeof (String), "ToLower");
+			EnsureMethodExists (typeof (String), "ToUpper");
+			EnsureMethodExists (typeof (String), "Trim");
+			EnsureMethodExists (typeof (Math), "Truncate", typeof (decimal));
+			EnsureMethodExists (typeof (Math), "Truncate", typeof (double));
+			EnsureMethodExists (typeof (Math), "Pow", typeof (double), typeof (double));
+			EnsureMethodExists (typeof (Guid), "NewGuid");
+			EnsureMethodExists (typeof (String), "Contains", typeof (string));
+			EnsureMethodExists (typeof (String), "IndexOf", typeof (string));
+			EnsureMethodExists (typeof (String), "StartsWith", typeof (string));
+			EnsureMethodExists (typeof (String), "EndsWith", typeof (string));
+			EnsureMethodExists (typeof (String), "Substring", typeof (int));
+			EnsureMethodExists (typeof (String), "Substring", typeof (int), typeof (int));
+			EnsureMethodExists (typeof (String), "Remove", typeof (int));
+			EnsureMethodExists (typeof (String), "Remove", typeof (int), typeof (int));
+			EnsureMethodExists (typeof (String), "IsNullOrEmpty", typeof (string));
+			EnsureMethodExists (typeof (String), "Concat", typeof (string), typeof (string));
+			EnsureMethodExists (typeof (String), "Concat", typeof (string), typeof (string), typeof (string));
+			EnsureMethodExists (typeof (String), "Concat", typeof (string), typeof (string), typeof (string), typeof (string));
+			EnsureMethodExists (typeof (String), "Concat", typeof (object), typeof (object));
+			EnsureMethodExists (typeof (String), "Concat", typeof (object), typeof (object), typeof (object));
+			EnsureMethodExists (typeof (String), "Concat", typeof (object), typeof (object), typeof (object), typeof (object));
+			EnsureMethodExists (typeof (String), "Concat", typeof (object[]));
+			EnsureMethodExists (typeof (String), "Concat", typeof (string[]));
+			EnsureMethodExists (typeof (String), "Trim", typeof (Char[]));
+			EnsureMethodExists (typeof (String), "TrimStart", typeof (Char[]));
+			EnsureMethodExists (typeof (String), "TrimEnd", typeof (Char[]));
+		}
+
 		[Test]
 		public void TestLocalVariableTypes ()
 		{