[Core] Added new WorkspaceObjectReader class

WorkspaceObjectReader replaces ProjectServiceExtension as extension proint
for providing custom project and solution loaders.

8 files changed, 141 insertions, 241 deletions

diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.addin.xml b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.addin.xml
index 14f7acfa0c..bf74bb84c8 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.addin.xml
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.addin.xml
@@ -84,10 +84,10 @@
 		</ExtensionNode>
 	</ExtensionPoint>
 
-	<ExtensionPoint path = "/MonoDevelop/ProjectModel/ProjectServiceExtensions" name = "Project service extensions">
-		<Description>Project service extensions. Specified classes must be a subclass of ProjectServiceExtension</Description>
+	<ExtensionPoint path = "/MonoDevelop/ProjectModel/WorkspaceObjectReaders" name = "Project service extensions">
+		<Description>WorkspaceObject readers. Specified classes must be a subclass of WorkspaceObjectReader</Description>
 		<ExtensionNode name="Class">
-			<Description>A subclass of ProjectServiceExtension.</Description>
+			<Description>A subclass of WorkspaceObjectReader.</Description>
 		</ExtensionNode>
 	</ExtensionPoint>
 
@@ -202,13 +202,13 @@
 		<Application id = "project-export" class = "MonoDevelop.Projects.ProjectConvertTool" description = "Project conversion tool"/>
 	</Extension>
 	
-	<Extension path = "/MonoDevelop/ProjectModel/ProjectServiceExtensions">
-		<Class id="InitialStep" class = "MonoDevelop.Projects.ProjectServiceExtension" />
-		<Class class = "MonoDevelop.Projects.CompiledAssemblyExtension" />
-		<Class class = "MonoDevelop.Projects.WorkspaceSerializationExtension" />
-		<Class class = "MonoDevelop.Projects.MSBuildSerializationExtension" />
-		<Class id="MidStep" class = "MonoDevelop.Projects.ProjectServiceExtension" />
-		<Class id="FinalStep" class = "MonoDevelop.Projects.ProjectServiceExtension" />
+	<Extension path = "/MonoDevelop/ProjectModel/WorkspaceObjectReaders">
+		<Class id="InitialStep" class = "MonoDevelop.Projects.DummyWorkspaceObjectReader" />
+		<Class id="CompiledAssembly" class = "MonoDevelop.Projects.CompiledAssemblyExtension" />
+		<Class id="Workspace" class = "MonoDevelop.Projects.WorkspaceSerializationExtension" />
+		<Class id="MSBuild" class = "MonoDevelop.Projects.MSBuildSerializationExtension" />
+		<Class id="MidStep" class = "MonoDevelop.Projects.DummyWorkspaceObjectReader" />
+		<Class id="FinalStep" class = "MonoDevelop.Projects.DummyWorkspaceObjectReader" />
 	</Extension>
 	
 	<Extension path = "/MonoDevelop/Core/FileSystemExtensions">
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj
index 2802a7a5cb..80bb13fa04 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core.csproj
@@ -113,9 +113,6 @@
     <Reference Include="System.ServiceModel" />
     <Reference Include="Microsoft.CSharp" />
     <Reference Include="Microsoft.Build.Engine" />
-    <Reference Include="System.Collections.Immutable">
-      <HintPath>..\..\..\packages\System.Collections.Immutable.1.1.33-beta\lib\portable-net45+win8+wp8+wpa81\System.Collections.Immutable.dll</HintPath>
-    </Reference>
     <Reference Include="Microsoft.Build" />
   </ItemGroup>
   <ItemGroup>
@@ -274,7 +271,6 @@
     <Compile Include="MonoDevelop.Projects\ExecutionContext.cs" />
     <Compile Include="MonoDevelop.Projects\BuildTool.cs" />
     <Compile Include="MonoDevelop.Projects\BuildEventHandler.cs" />
-    <Compile Include="MonoDevelop.Projects\ProjectServiceExtension.cs" />
     <Compile Include="MonoDevelop.Projects\CustomCommandCollection.cs" />
     <Compile Include="MonoDevelop.Projects\CustomCommand.cs" />
     <Compile Include="MonoDevelop.Projects\CustomCommandType.cs" />
@@ -523,6 +519,7 @@
     <Compile Include="MonoDevelop.Projects.Formats.MSBuild\DefaultMSBuildEngine.cs" />
     <Compile Include="MonoDevelop.Projects\SolutionDataSectionAttribute.cs" />
     <Compile Include="MonoDevelop.Core.Serialization\DataDeletedValue.cs" />
+    <Compile Include="MonoDevelop.Projects\WorkspaceObjectReader.cs" />
   </ItemGroup>
   <ItemGroup>
     <None Include="Makefile.am" />
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/CompiledAssemblyProject.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/CompiledAssemblyProject.cs
index a74c61e9a0..4809bf5bb5 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/CompiledAssemblyProject.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/CompiledAssemblyProject.cs
@@ -204,25 +204,20 @@ namespace MonoDevelop.Projects
 		}
 	}
 	
-	public class CompiledAssemblyExtension: ProjectServiceExtension
+	public class CompiledAssemblyExtension: WorkspaceObjectReader
 	{
-		public override bool FileIsObjectOfType (string fileName, Type type)
+		public override bool CanRead (FilePath file, Type expectedType)
 		{
-			if ((type.IsAssignableFrom (typeof(SolutionItem))|| type.IsAssignableFrom (typeof(Solution))) && (fileName.ToLower().EndsWith (".exe") || fileName.ToLower().EndsWith (".dll")))
-				return true;
-			return base.FileIsObjectOfType (fileName, type);
+			return (expectedType.IsAssignableFrom (typeof(SolutionItem)) || expectedType.IsAssignableFrom (typeof(Solution))) && (file.Extension.ToLower() == ".exe" || file.Extension.ToLower() ==  ".dll");
 		}
 
 		public override Task<SolutionItem> LoadSolutionItem (ProgressMonitor monitor, SolutionLoadContext ctx, string fileName, MSBuildFileFormat expectedFormat, string typeGuid, string itemGuid)
 		{
-			if (fileName.ToLower().EndsWith (".exe") || fileName.ToLower().EndsWith (".dll")) {
-				return Task<SolutionItem>.Factory.StartNew (delegate {
-					CompiledAssemblyProject p = new CompiledAssemblyProject ();
-					p.LoadFrom (fileName);
-					return p;
-				});
-			}
-			return base.LoadSolutionItem (monitor, ctx, fileName, expectedFormat, typeGuid, itemGuid);
+			return Task<SolutionItem>.Factory.StartNew (delegate {
+				CompiledAssemblyProject p = new CompiledAssemblyProject ();
+				p.LoadFrom (fileName);
+				return p;
+			});
 		}
 	}
 }
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/MSBuildSerializationExtension.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/MSBuildSerializationExtension.cs
index 9afec767d9..d6f22edcc4 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/MSBuildSerializationExtension.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/MSBuildSerializationExtension.cs
@@ -30,15 +30,15 @@ using System.Threading.Tasks;
 
 namespace MonoDevelop.Projects
 {
-	class MSBuildSerializationExtension: ProjectServiceExtension
+	class MSBuildSerializationExtension: WorkspaceObjectReader
 	{
-		public override bool FileIsObjectOfType (string file, Type type)
+		public override bool CanRead (FilePath file, Type expectedType)
 		{
 			foreach (var f in MSBuildFileFormat.GetSupportedFormats ()) {
-				if (f.CanReadFile (file, type))
+				if (f.CanReadFile (file, expectedType))
 					return true;
 			}
-			return base.FileIsObjectOfType (file, type);
+			return false;
 		}
 
 		public override async Task<SolutionItem> LoadSolutionItem (ProgressMonitor monitor, SolutionLoadContext ctx, string fileName, MSBuildFileFormat expectedFormat, string typeGuid, string itemGuid)
@@ -47,7 +47,7 @@ namespace MonoDevelop.Projects
 				if (f.CanReadFile (fileName, typeof(SolutionItem)))
 					return await MSBuildProjectService.LoadItem (monitor, fileName, f, typeGuid, itemGuid, ctx);
 			}
-			return await base.LoadSolutionItem (monitor, ctx, fileName, expectedFormat, typeGuid, itemGuid);
+			throw new NotSupportedException ();
 		}
 
 		public override async Task<WorkspaceItem> LoadWorkspaceItem (ProgressMonitor monitor, string fileName)
@@ -56,7 +56,7 @@ namespace MonoDevelop.Projects
 				if (f.CanReadFile (fileName, typeof(WorkspaceItem)))
 					return (WorkspaceItem) await f.ReadFile (fileName, typeof(WorkspaceItem), monitor);
 			}
-			return await base.LoadWorkspaceItem (monitor, fileName);
+			throw new NotSupportedException ();
 		}
 	}
 }
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs
index 12ce44ff8c..0928b90361 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectService.cs
@@ -50,9 +50,8 @@ namespace MonoDevelop.Projects
 	public class ProjectService
 	{
 		DataContext dataContext = new DataContext ();
-		ProjectServiceExtension defaultExtensionChain;
-		DefaultProjectServiceExtension extensionChainTerminator = new DefaultProjectServiceExtension ();
-		
+		WorkspaceObjectReader defaultExtensionChain;
+
 		TargetFramework defaultTargetFramework;
 		
 		string defaultPlatformTarget = "x86";
@@ -63,6 +62,7 @@ namespace MonoDevelop.Projects
 		
 		const string SerializableClassesExtensionPath = "/MonoDevelop/ProjectModel/SerializableClasses";
 		const string ProjectBindingsExtensionPath = "/MonoDevelop/ProjectModel/ProjectBindings";
+		const string WorkspaceObjectReadersPath = "/MonoDevelop/ProjectModel/WorkspaceObjectReaders";
 
 		internal const string ProjectModelExtensionsPath = "/MonoDevelop/ProjectModel/ProjectModelExtensions";
 
@@ -78,27 +78,19 @@ namespace MonoDevelop.Projects
 			get { return dataContext; }
 		}
 		
-		internal ProjectServiceExtension GetExtensionChain ()
+		IEnumerable<WorkspaceObjectReader> GetObjectReaders ()
 		{
-			if (defaultExtensionChain == null) {
-				ProjectServiceExtension[] extensions = AddinManager.GetExtensionObjects<ProjectServiceExtension> ("/MonoDevelop/ProjectModel/ProjectServiceExtensions");
-				defaultExtensionChain = CreateExtensionChain (extensions);
-			}
-			return defaultExtensionChain;
+			return AddinManager.GetExtensionObjects<WorkspaceObjectReader> (WorkspaceObjectReadersPath);
 		}
-		
-		ProjectServiceExtension CreateExtensionChain (ProjectServiceExtension[] extensions)
+
+		WorkspaceObjectReader GetObjectReaderForFile (FilePath file, Type type)
 		{
-			if (extensions.Length > 0) {
-				for (int n=0; n<extensions.Length - 1; n++)
-					extensions [n].Next = extensions [n + 1];
-				extensions [extensions.Length - 1].Next = extensionChainTerminator;
-				return extensions [0];
-			} else {
-				return extensionChainTerminator;
-			}
+			foreach (var r in GetObjectReaders ())
+				if (r.CanRead (file, type))
+					return r;
+			return null;
 		}
-		
+
 		public string DefaultPlatformTarget {
 			get { return defaultPlatformTarget; }
 			set { defaultPlatformTarget = value; }
@@ -129,7 +121,10 @@ namespace MonoDevelop.Projects
 				file = Path.GetFullPath (file);
 				using (Counters.ReadSolutionItem.BeginTiming ("Read project " + file)) {
 					file = GetTargetFile (file);
-					SolutionItem loadedItem = await GetExtensionChain ().LoadSolutionItem (monitor, ctx, file, format, typeGuid, itemGuid);
+					var r = GetObjectReaderForFile (file, typeof(SolutionItem));
+					if (r == null)
+						throw new UnknownSolutionItemTypeException ();
+					SolutionItem loadedItem = await r.LoadSolutionItem (monitor, ctx, file, format, typeGuid, itemGuid);
 					if (loadedItem != null)
 						loadedItem.NeedsReload = false;
 					return loadedItem;
@@ -182,7 +177,10 @@ namespace MonoDevelop.Projects
 				string fullpath = file.ResolveLinks ().FullPath;
 				using (Counters.ReadWorkspaceItem.BeginTiming ("Read solution " + file)) {
 					fullpath = GetTargetFile (fullpath);
-					WorkspaceItem item = await GetExtensionChain ().LoadWorkspaceItem (monitor, fullpath) as WorkspaceItem;
+					var r = GetObjectReaderForFile (file, typeof(WorkspaceItem));
+					if (r == null)
+						throw new InvalidOperationException ("Invalid file format: " + file);
+					WorkspaceItem item = await r.LoadWorkspaceItem (monitor, fullpath);
 					if (item != null)
 						item.NeedsReload = false;
 					else
@@ -381,19 +379,17 @@ namespace MonoDevelop.Projects
 		public bool FileIsObjectOfType (FilePath file, Type type)
 		{
 			var filename = GetTargetFile (file);
-			return GetExtensionChain ().FileIsObjectOfType (filename, type);
+			return GetObjectReaderForFile (filename, type) != null;
 		}
 
 		public bool IsSolutionItemFile (FilePath file)
 		{
-			var filename = GetTargetFile (file);
-			return GetExtensionChain ().FileIsObjectOfType (filename, typeof(SolutionItem));
+			return FileIsObjectOfType (file, typeof(SolutionItem));
 		}
 
 		public bool IsWorkspaceItemFile (FilePath file)
 		{
-			var filename = GetTargetFile (file);
-			return GetExtensionChain ().FileIsObjectOfType (filename, typeof(WorkspaceItem));
+			return FileIsObjectOfType (file, typeof(WorkspaceItem));
 		}
 		
 		internal void InitializeDataContext (DataContext ctx)
@@ -435,24 +431,6 @@ namespace MonoDevelop.Projects
 		}
 	}
 	
-	internal class DefaultProjectServiceExtension: ProjectServiceExtension
-	{
-		public override bool FileIsObjectOfType (string file, Type type)
-		{
-			return false;
-		}
-
-		public override Task<SolutionItem> LoadSolutionItem (ProgressMonitor monitor, SolutionLoadContext ctx, string fileName, MSBuildFileFormat expectedFormat, string typeGuid, string itemGuid)
-		{
-			return Task.FromResult ((SolutionItem)null);
-		}
-		
-		public override Task<WorkspaceItem> LoadWorkspaceItem (ProgressMonitor monitor, string fileName)
-		{
-			return Task.FromResult ((WorkspaceItem)null);
-		}
-	}	
-	
 	internal static class Counters
 	{
 		public static Counter ItemsInMemory = InstrumentationService.CreateCounter ("Projects in memory", "Project Model");
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs
deleted file mode 100644
index 60788b9ee5..0000000000
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/ProjectServiceExtension.cs
+++ /dev/null
@@ -1,133 +0,0 @@
-// ProjectServiceExtension.cs
-//
-// Author:
-//   Lluis Sanchez Gual <lluis@novell.com>
-//
-// Copyright (c) 2007 Novell, Inc (http://www.novell.com)
-//
-// Permission is hereby granted, free of charge, to any person obtaining a copy
-// of this software and associated documentation files (the "Software"), to deal
-// in the Software without restriction, including without limitation the rights
-// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-// copies of the Software, and to permit persons to whom the Software is
-// furnished to do so, subject to the following conditions:
-//
-// The above copyright notice and this permission notice shall be included in
-// all copies or substantial portions of the Software.
-//
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-// THE SOFTWARE.
-//
-//
-
-
-using System;
-using System.Collections.Generic;
-using MonoDevelop.Core;
-using MonoDevelop.Projects.Extensions;
-using MonoDevelop.Core.Execution;
-using System.Threading.Tasks;
-using MonoDevelop.Projects.Formats.MSBuild;
-
-namespace MonoDevelop.Projects
-{
-	public class ProjectServiceExtension
-	{
-		internal ProjectServiceExtension Next;
-
-		internal ProjectServiceExtension GetNext (WorkspaceObject item)
-		{
-			if (Next.SupportsItem (item))
-				return Next;
-			else
-				return Next.GetNext (item);
-		}
-		
-		public virtual bool SupportsItem (WorkspaceObject item)
-		{
-			return true;
-		}
-
-		public virtual bool FileIsObjectOfType (string file, Type type)
-		{
-			return GetNext (UnknownItem.Instance).FileIsObjectOfType (file, type);
-		}
-		
-		public virtual Task<SolutionItem> LoadSolutionItem (ProgressMonitor monitor, SolutionLoadContext ctx, string fileName, MSBuildFileFormat expectedFormat, string typeGuid, string itemGuid)
-		{
-			return GetNext (UnknownItem.Instance).LoadSolutionItem (monitor, ctx, fileName, expectedFormat, typeGuid, itemGuid);
-		}
-		
-		public virtual Task<WorkspaceItem> LoadWorkspaceItem (ProgressMonitor monitor, string fileName)
-		{
-			return GetNext (UnknownItem.Instance).LoadWorkspaceItem (monitor, fileName);
-		}
-	}
-
-	public class BuildData
-	{
-		public ProjectItemCollection Items { get; internal set; }
-		public DotNetProjectConfiguration Configuration { get; internal set; }
-		public ConfigurationSelector ConfigurationSelector { get; internal set; }
-	}
-	
-	class UnknownItem: WorkspaceObject, IBuildTarget
-	{
-		public static UnknownItem Instance = new UnknownItem ();
-
-		public Task<BuildResult> Build (ProgressMonitor monitor, ConfigurationSelector configuration, bool buildReferencedTargets = false)
-		{
-			return Task.FromResult (BuildResult.Success);
-		}
-		
-		public Task<BuildResult> Clean (ProgressMonitor monitor, ConfigurationSelector configuration)
-		{
-			return Task.FromResult (BuildResult.Success);
-		}
-
-		public Task Execute (ProgressMonitor monitor, ExecutionContext context, ConfigurationSelector configuration)
-		{
-			throw new System.NotImplementedException();
-		}
-		
-		public bool CanExecute (ExecutionContext context, ConfigurationSelector configuration)
-		{
-			return false;
-		}
-		
-		public Task PrepareExecution (ProgressMonitor monitor, ExecutionContext context, ConfigurationSelector configuration)
-		{
-			return Task.FromResult (true);
-		}
-
-		public bool NeedsBuilding (ConfigurationSelector configuration)
-		{
-			return false;
-		}
-
-		public IEnumerable<IBuildTarget> GetExecutionDependencies ()
-		{
-			yield break;
-		}
-
-		protected override string OnGetName ()
-		{
-			return "Unknown";
-		}
-
-		protected override string OnGetBaseDirectory ()
-		{
-			return FilePath.Empty;
-		}
-
-		protected override string OnGetItemDirectory ()
-		{
-			return FilePath.Empty;
-		}
-	}
-}
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/WorkspaceObjectReader.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/WorkspaceObjectReader.cs
new file mode 100644
index 0000000000..681dfa9362
--- /dev/null
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/WorkspaceObjectReader.cs
@@ -0,0 +1,67 @@
+// ProjectServiceExtension.cs
+//
+// Author:
+//   Lluis Sanchez Gual <lluis@novell.com>
+//
+// Copyright (c) 2007 Novell, Inc (http://www.novell.com)
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+//
+
+
+using System;
+using MonoDevelop.Core;
+using System.Threading.Tasks;
+using MonoDevelop.Projects.Formats.MSBuild;
+
+namespace MonoDevelop.Projects
+{
+	public abstract class WorkspaceObjectReader
+	{
+		internal WorkspaceObjectReader Next;
+
+		public abstract bool CanRead (FilePath file, Type expectedType);
+
+		public virtual Task<SolutionItem> LoadSolutionItem (ProgressMonitor monitor, SolutionLoadContext ctx, string fileName, MSBuildFileFormat expectedFormat, string typeGuid, string itemGuid)
+		{
+			throw new NotSupportedException ();
+		}
+		
+		public virtual Task<WorkspaceItem> LoadWorkspaceItem (ProgressMonitor monitor, string fileName)
+		{
+			throw new NotSupportedException ();
+		}
+	}
+
+	class DummyWorkspaceObjectReader: WorkspaceObjectReader
+	{
+		public override bool CanRead (FilePath file, Type expectedType)
+		{
+			return false;
+		}
+	}
+
+	public class BuildData
+	{
+		public ProjectItemCollection Items { get; internal set; }
+		public DotNetProjectConfiguration Configuration { get; internal set; }
+		public ConfigurationSelector ConfigurationSelector { get; internal set; }
+	}
+}
diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/WorkspaceSerializationExtension.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/WorkspaceSerializationExtension.cs
index 2c5d9063a1..ce455dd0e5 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/WorkspaceSerializationExtension.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Projects/WorkspaceSerializationExtension.cs
@@ -33,48 +33,44 @@ using MonoDevelop.Projects.Formats.MD1;
 
 namespace MonoDevelop.Projects
 {
-	class WorkspaceSerializationExtension: ProjectServiceExtension
+	class WorkspaceSerializationExtension: WorkspaceObjectReader
 	{
-		public override bool FileIsObjectOfType (string file, Type type)
+		public override bool CanRead (FilePath file, Type expectedType)
 		{
-			if (type.IsAssignableFrom (typeof(Workspace))) {
+			if (expectedType.IsAssignableFrom (typeof(Workspace))) {
 				string ext = Path.GetExtension (file).ToLower ();
 				if (ext == ".mdw")
 					return true;
 			}
-			return base.FileIsObjectOfType (file, type);
+			return false;
 		}
 
-		public override async Task<WorkspaceItem> LoadWorkspaceItem (ProgressMonitor monitor, string fileName)
+		public override Task<WorkspaceItem> LoadWorkspaceItem (ProgressMonitor monitor, string fileName)
 		{
-			string ext = Path.GetExtension (fileName).ToLower ();
-			if (ext == ".mdw")
-				return await ReadWorkspaceItemFile (fileName, monitor);
-
-			return await base.LoadWorkspaceItem (monitor, fileName);
+			return Task<WorkspaceItem>.Factory.StartNew (delegate {
+				return ReadWorkspaceItemFile (fileName, monitor);
+			});
 		}
 
-		Task<WorkspaceItem> ReadWorkspaceItemFile (FilePath fileName, ProgressMonitor monitor)
+		WorkspaceItem ReadWorkspaceItemFile (FilePath fileName, ProgressMonitor monitor)
 		{
-			return Task<WorkspaceItem>.Factory.StartNew (delegate {
-				XmlTextReader reader = new XmlTextReader (new StreamReader (fileName));
-				try {
-					monitor.BeginTask (string.Format (GettextCatalog.GetString ("Loading workspace item: {0}"), fileName), 1);
-					reader.MoveToContent ();
-					XmlDataSerializer ser = new XmlDataSerializer (MD1ProjectService.DataContext);
-					ser.SerializationContext.BaseFile = fileName;
-					ser.SerializationContext.ProgressMonitor = monitor;
-					WorkspaceItem entry = (WorkspaceItem)ser.Deserialize (reader, typeof(WorkspaceItem));
-					entry.FileName = fileName;
-					return entry;
-				} catch (Exception ex) {
-					monitor.ReportError (string.Format (GettextCatalog.GetString ("Could not load solution item: {0}"), fileName), ex);
-					throw;
-				} finally {
-					monitor.EndTask ();
-					reader.Close ();
-				}
-			});
+			XmlTextReader reader = new XmlTextReader (new StreamReader (fileName));
+			try {
+				monitor.BeginTask (string.Format (GettextCatalog.GetString ("Loading workspace item: {0}"), fileName), 1);
+				reader.MoveToContent ();
+				XmlDataSerializer ser = new XmlDataSerializer (MD1ProjectService.DataContext);
+				ser.SerializationContext.BaseFile = fileName;
+				ser.SerializationContext.ProgressMonitor = monitor;
+				WorkspaceItem entry = (WorkspaceItem)ser.Deserialize (reader, typeof(WorkspaceItem));
+				entry.FileName = fileName;
+				return entry;
+			} catch (Exception ex) {
+				monitor.ReportError (string.Format (GettextCatalog.GetString ("Could not load solution item: {0}"), fileName), ex);
+				throw;
+			} finally {
+				monitor.EndTask ();
+				reader.Close ();
+			}
 		}
 	}
 }