Allow Razor files to be additional documents in a misc files project (#78267)

Fixes a startup crash in VS Code if a .razor or .cshtml file is restored
in the workspace.

Part of dotnet/razor#11759

Author: davidwengier

src/Features/Core/Portable/Workspace/MiscellaneousFileUtilities.cs

@@ -27,7 +27,11 @@ internal static ProjectInfo CreateMiscellaneousProjectInfoForDocument(
         var fileExtension = PathUtilities.GetExtension(filePath);
         var fileName = PathUtilities.GetFileName(filePath);
 
-        var languageServices = services.GetLanguageServices(languageInformation.LanguageName);
+        // For Razor files we need to override the language name to C# as thats what code is generated
+        var isRazor = languageInformation.LanguageName == "Razor";
+        var languageName = isRazor ? LanguageNames.CSharp : languageInformation.LanguageName;
+
+        var languageServices = services.GetLanguageServices(languageName);
         var compilationOptions = languageServices.GetService<ICompilationFactoryService>()?.GetDefaultCompilationOptions();
 
         // Use latest language version which is more permissive, as we cannot find out language version of the project which the file belongs to
@@ -63,15 +67,16 @@ internal static ProjectInfo CreateMiscellaneousProjectInfoForDocument(
                 version: VersionStamp.Create(),
                 name: FeaturesResources.Miscellaneous_Files,
                 assemblyName: assemblyName,
-                language: languageInformation.LanguageName,
+                language: languageName,
                 compilationOutputInfo: default,
                 checksumAlgorithm: checksumAlgorithm,
                 // Miscellaneous files projects are never fully loaded since, by definition, it won't know
                 // what the full set of information is except when the file is script code.
                 hasAllInformation: sourceCodeKind == SourceCodeKind.Script),
             compilationOptions: compilationOptions,
             parseOptions: parseOptions,
-            documents: [documentInfo],
+            documents: isRazor ? null : [documentInfo],
+            additionalDocuments: isRazor ? [documentInfo] : null,
             metadataReferences: metadataReferences);
 
         return projectInfo;

src/LanguageServer/Protocol/Workspaces/LspMiscellaneousFilesWorkspace.cs

@@ -36,7 +36,7 @@ internal sealed class LspMiscellaneousFilesWorkspace(ILspServices lspServices, I
     /// Calls to this method and <see cref="TryRemoveMiscellaneousDocument(Uri, bool)"/> are made
     /// from LSP text sync request handling which do not run concurrently.
     /// </summary>
-    public Document? AddMiscellaneousDocument(Uri uri, SourceText documentText, string languageId, ILspLogger logger)
+    public TextDocument? AddMiscellaneousDocument(Uri uri, SourceText documentText, string languageId, ILspLogger logger)
     {
         var documentFilePath = ProtocolConversions.GetDocumentFilePathFromUri(uri);
 
@@ -63,6 +63,12 @@ internal sealed class LspMiscellaneousFilesWorkspace(ILspServices lspServices, I
             this, documentFilePath, sourceTextLoader, languageInformation, documentText.ChecksumAlgorithm, Services.SolutionServices, []);
         OnProjectAdded(projectInfo);
 
+        if (languageInformation.LanguageName == "Razor")
+        {
+            var docId = projectInfo.AdditionalDocuments.Single().Id;
+            return CurrentSolution.GetRequiredAdditionalDocument(docId);
+        }
+
         var id = projectInfo.Documents.Single().Id;
         return CurrentSolution.GetRequiredDocument(id);
     }

src/LanguageServer/ProtocolUnitTests/Miscellaneous/LspMiscellaneousFilesWorkspaceTests.cs

@@ -180,6 +180,34 @@ void M()
         Assert.Null(GetMiscellaneousDocument(testLspServer));
     }
 
+    [Theory, CombinatorialData]
+    public async Task TestLooseFile_RazorFile(bool mutatingLspWorkspace)
+    {
+        var source = "<div></div>";
+
+        // Create a server that supports LSP misc files and verify no misc files present.
+        await using var testLspServer = await CreateTestLspServerAsync(string.Empty, mutatingLspWorkspace, new InitializationOptions { ServerKind = WellKnownLspServerKinds.CSharpVisualBasicLspServer });
+        Assert.Null(GetMiscellaneousDocument(testLspServer));
+        Assert.Null(GetMiscellaneousAdditionalDocument(testLspServer));
+
+        // Open an empty loose file and make a request to verify it gets added to the misc workspace.
+        var looseFileUri = ProtocolConversions.CreateAbsoluteUri(@"C:\SomeFile.razor");
+        await testLspServer.OpenDocumentAsync(looseFileUri, source).ConfigureAwait(false);
+
+        // Trigger a request and assert we got a file in the misc workspace.
+        await AssertFileInMiscWorkspaceAsync(testLspServer, looseFileUri).ConfigureAwait(false);
+        Assert.Null(GetMiscellaneousDocument(testLspServer));
+        Assert.NotNull(GetMiscellaneousAdditionalDocument(testLspServer));
+
+        // Trigger another request and assert we got a file in the misc workspace.
+        await AssertFileInMiscWorkspaceAsync(testLspServer, looseFileUri).ConfigureAwait(false);
+        Assert.NotNull(GetMiscellaneousAdditionalDocument(testLspServer));
+
+        await testLspServer.CloseDocumentAsync(looseFileUri).ConfigureAwait(false);
+        Assert.Null(GetMiscellaneousDocument(testLspServer));
+        Assert.Null(GetMiscellaneousAdditionalDocument(testLspServer));
+    }
+
     [Theory, CombinatorialData]
     public async Task TestLooseFile_RequestedTwiceAndClosed(bool mutatingLspWorkspace)
     {
@@ -306,7 +334,12 @@ private static async Task AssertFileInMainWorkspaceAsync(TestLspServer testLspSe
 
     private static Document? GetMiscellaneousDocument(TestLspServer testLspServer)
     {
-        return testLspServer.GetManagerAccessor().GetLspMiscellaneousFilesWorkspace()!.CurrentSolution.Projects.SingleOrDefault()?.Documents.Single();
+        return testLspServer.GetManagerAccessor().GetLspMiscellaneousFilesWorkspace()!.CurrentSolution.Projects.SingleOrDefault()?.Documents.SingleOrDefault();
+    }
+
+    private static TextDocument? GetMiscellaneousAdditionalDocument(TestLspServer testLspServer)
+    {
+        return testLspServer.GetManagerAccessor().GetLspMiscellaneousFilesWorkspace()!.CurrentSolution.Projects.SingleOrDefault()?.AdditionalDocuments.SingleOrDefault();
     }
 
     private static async Task<LSP.Hover> RunGetHoverAsync(TestLspServer testLspServer, LSP.Location caret)