Add Mac implementation of VisualStudioWorkspaceAccessor new APIs.

- The Mac implementation does not have fallback logic like the windows variant because Workspaces in VS mac world are spun up / torn down regularly. We don't want to be tracking down bugs that involve us adding services or Razor logic to Workspaces that have nothing to do with Razor.
- Added a test for the `DefaultVisualStudioWorkspaceAccessor`. Could not add other tests due to limitations of MonoDevelop's abstractions.

#1989

src/Microsoft.VisualStudio.Mac.LanguageServices.Razor/DefaultVisualStudioWorkspaceAccessor.cs

@@ -1,11 +1,13 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.ComponentModel.Composition;
-using Microsoft.CodeAnalysis;
 using Microsoft.VisualStudio.Editor.Razor;
 using Microsoft.VisualStudio.Text;
 using MonoDevelop.Ide.TypeSystem;
+using MonoDevelop.Projects;
+using Workspace = Microsoft.CodeAnalysis.Workspace;
 
 namespace Microsoft.VisualStudio.Mac.LanguageServices.Razor
 {
@@ -13,16 +15,63 @@ namespace Microsoft.VisualStudio.Mac.LanguageServices.Razor
     [Export(typeof(VisualStudioWorkspaceAccessor))]
     internal class DefaultVisualStudioWorkspaceAccessor : VisualStudioWorkspaceAccessor
     {
-        public DefaultVisualStudioWorkspaceAccessor()
+        private readonly TextBufferProjectService _projectService;
+
+        [ImportingConstructor]
+        public DefaultVisualStudioWorkspaceAccessor(TextBufferProjectService projectService)
         {
-            Workspace = TypeSystemService.Workspace;
+            if (projectService == null)
+            {
+                throw new ArgumentNullException(nameof(projectService));
+            }
+
+            _projectService = projectService;
         }
 
-        public override Workspace Workspace { get; }
+        public override Workspace Workspace => TypeSystemService.Workspace;
 
         public override bool TryGetWorkspace(ITextBuffer textBuffer, out Workspace workspace)
         {
-            throw new System.NotImplementedException();
+            if (textBuffer == null)
+            {
+                throw new ArgumentNullException(nameof(textBuffer));
+            }
+
+            // We do a best effort approach in this method to get the workspace that belongs to the TextBuffer.
+            // Below we try and find the project and then the solution that contains the given text buffer. If 
+            // we're able to find both the project and solution then we use the solution to look up the corresponding 
+            // Workspace using MonoDevelops TypeSystemService.
+
+            var hostProject = (DotNetProject)_projectService.GetHostProject(textBuffer);
+            if (hostProject == null)
+            {
+                // Does not have a host project.
+                workspace = null;
+                return false;
+            }
+
+            var hostSolution = hostProject.ParentSolution;
+            if (hostSolution == null)
+            {
+                // Project does not have a solution
+                workspace = null;
+                return false;
+            }
+
+            workspace = TypeSystemService.GetWorkspace(hostSolution);
+
+            // Workspace cannot be null at this point. If TypeSystemService.GetWorkspace isn't able to find a corresponding
+            // workspace it returns an empty workspace. Therefore, in order to see if we have a valid workspace we need to
+            // cross-check it against the list of active non-empty workspaces.
+
+            if (!TypeSystemService.AllWorkspaces.Contains(workspace))
+            {
+                // We were returned the empty workspace which is equivalent to us not finding a valid workspace for our text buffer.
+                workspace = null;
+                return false;
+            }
+
+            return true;
         }
     }
-}
+}

test/Microsoft.VisualStudio.Mac.LanguageServices.Razor.Test/DefaultVisualStudioWorkspaceAccessorTest.cs

@@ -0,0 +1,33 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.VisualStudio.Editor.Razor;
+using Microsoft.VisualStudio.Text;
+using Moq;
+using Xunit;
+
+namespace Microsoft.VisualStudio.Mac.LanguageServices.Razor
+{
+    public class DefaultVisualStudioWorkspaceAccessorTest
+    {
+        [Fact]
+        public void TryGetWorkspace_NoHostProject_ReturnsFalse()
+        {
+            // Arrange
+            var workspaceAccessor = new DefaultVisualStudioWorkspaceAccessor(Mock.Of<TextBufferProjectService>());
+            var textBuffer = Mock.Of<ITextBuffer>();
+
+            // Act
+            var result = workspaceAccessor.TryGetWorkspace(textBuffer, out var workspace);
+
+            // Assert
+            Assert.False(result);
+        }
+
+        // -------------------------------------------------------------------------------------------
+        // Purposefully do not have any more tests here because that would involve mocking MonoDevelop 
+        // types. The default constructors for the Solution / DotNetProject MonoDevelop types change
+        // static classes (they assume they're being created in an IDE).
+        // -------------------------------------------------------------------------------------------
+    }
+}