Make cohosting win over legacy editor (#11959)

Fixes #11941

This change means that if cohosting is on, we'll always use LSP, except
for .NET Framework projects which will fall back to the really really
legacy legacy editor. That editor has no interaction with any of our
code, except the VS editor does send us a couple of LSP methods (because
dynamic registration is by file extension, not content type) so we have
to be a tiny bit defensive.

Author: davidwengier

src/Razor/src/Microsoft.CodeAnalysis.Razor.CohostingShared/DocumentSymbol/CohostDocumentSymbolEndpoint.cs

@@ -5,7 +5,7 @@
 using System.Composition;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Razor;
+using Microsoft.AspNetCore.Razor.Threading;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor.Cohost;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor.Features;
@@ -50,7 +50,16 @@ public ImmutableArray<Registration> GetRegistrations(VSInternalClientCapabilitie
         => request.TextDocument.ToRazorTextDocumentIdentifier();
 
     protected override Task<SumType<DocumentSymbol[], SymbolInformation[]>?> HandleRequestAsync(DocumentSymbolParams request, RazorCohostRequestContext context, CancellationToken cancellationToken)
-        => HandleRequestAsync(context.TextDocument.AssumeNotNull(), _useHierarchicalSymbols, cancellationToken);
+    {
+        // The editor can send us a document symbol request in a .NET Framework project for some reason, so we have to be
+        // a little defensive here.
+        if (context.TextDocument is null)
+        {
+            return SpecializedTasks.Default<SumType<DocumentSymbol[], SymbolInformation[]>?>();
+        }
+
+        return HandleRequestAsync(context.TextDocument, _useHierarchicalSymbols, cancellationToken);
+    }
 
     private async Task<SumType<DocumentSymbol[], SymbolInformation[]>?> HandleRequestAsync(TextDocument razorDocument, bool useHierarchicalSymbols, CancellationToken cancellationToken)
     {

src/Razor/src/Microsoft.CodeAnalysis.Razor.CohostingShared/LinkedEditingRange/CohostLinkedEditingRangeEndpoint.cs

@@ -5,7 +5,7 @@
 using System.Composition;
 using System.Threading;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Razor;
+using Microsoft.AspNetCore.Razor.Threading;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor.Cohost;
 using Microsoft.CodeAnalysis.ExternalAccess.Razor.Features;
@@ -50,7 +50,16 @@ public ImmutableArray<Registration> GetRegistrations(VSInternalClientCapabilitie
         => request.TextDocument.ToRazorTextDocumentIdentifier();
 
     protected override Task<LinkedEditingRanges?> HandleRequestAsync(LinkedEditingRangeParams request, RazorCohostRequestContext context, CancellationToken cancellationToken)
-        => HandleRequestAsync(request, context.TextDocument.AssumeNotNull(), cancellationToken);
+    {
+        // The editor can send us a linked editing range request in a .NET Framework project for some reason, so we have to be
+        // a little defensive here.
+        if (context.TextDocument is null)
+        {
+            return SpecializedTasks.Null<LinkedEditingRanges>();
+        }
+
+        return HandleRequestAsync(request, context.TextDocument, cancellationToken);
+    }
 
     private async Task<LinkedEditingRanges?> HandleRequestAsync(LinkedEditingRangeParams request, TextDocument razorDocument, CancellationToken cancellationToken)
     {

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/ILspEditorFeatureDetector.cs

@@ -16,6 +16,11 @@ internal interface ILspEditorFeatureDetector
     /// </summary>
     bool IsLspEditorSupported(string documentFilePath);
 
+    /// <summary>
+    /// Determines whether the project containing the given document is a .NET Core project.
+    /// </summary>
+    bool IsDotNetCoreProject(string documentFilePath);
+
     /// <summary>
     /// A remote client is a LiveShare guest or a Codespaces instance
     /// </summary>

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/LanguageClient/CSHTMLFilePathToContentTypeProvider.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System.ComponentModel.Composition;
+using Microsoft.CodeAnalysis.Razor.Workspaces;
 using Microsoft.VisualStudio.Utilities;
 
 namespace Microsoft.VisualStudio.Razor.LanguageClient;
@@ -12,7 +13,8 @@ namespace Microsoft.VisualStudio.Razor.LanguageClient;
 [method: ImportingConstructor]
 internal class CSHTMLFilePathToContentTypeProvider(
     IContentTypeRegistryService contentTypeRegistryService,
-    ILspEditorFeatureDetector lspEditorFeatureDetector)
-    : RazorFilePathToContentTypeProviderBase(contentTypeRegistryService, lspEditorFeatureDetector)
+    ILspEditorFeatureDetector lspEditorFeatureDetector,
+    LanguageServerFeatureOptions options)
+    : RazorFilePathToContentTypeProviderBase(contentTypeRegistryService, lspEditorFeatureDetector, options)
 {
 }

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/LanguageClient/RazorFilePathToContentTypeProvider.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System.ComponentModel.Composition;
+using Microsoft.CodeAnalysis.Razor.Workspaces;
 using Microsoft.VisualStudio.Utilities;
 
 namespace Microsoft.VisualStudio.Razor.LanguageClient;
@@ -12,7 +13,8 @@ namespace Microsoft.VisualStudio.Razor.LanguageClient;
 [method: ImportingConstructor]
 internal class RazorFilePathToContentTypeProvider(
     IContentTypeRegistryService contentTypeRegistryService,
-    ILspEditorFeatureDetector lspEditorFeatureDetector)
-    : RazorFilePathToContentTypeProviderBase(contentTypeRegistryService, lspEditorFeatureDetector)
+    ILspEditorFeatureDetector lspEditorFeatureDetector,
+    LanguageServerFeatureOptions options)
+    : RazorFilePathToContentTypeProviderBase(contentTypeRegistryService, lspEditorFeatureDetector, options)
 {
 }

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/LanguageClient/RazorFilePathToContentTypeProviderBase.cs

@@ -2,33 +2,49 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System.Diagnostics.CodeAnalysis;
+using Microsoft.CodeAnalysis.Razor.Workspaces;
 using Microsoft.VisualStudio.Utilities;
 
 namespace Microsoft.VisualStudio.Razor.LanguageClient;
 
-internal abstract class RazorFilePathToContentTypeProviderBase : IFilePathToContentTypeProvider
+internal abstract class RazorFilePathToContentTypeProviderBase(
+    IContentTypeRegistryService contentTypeRegistryService,
+    ILspEditorFeatureDetector lspEditorFeatureDetector,
+    LanguageServerFeatureOptions options) : IFilePathToContentTypeProvider
 {
-    private readonly IContentTypeRegistryService _contentTypeRegistryService;
-    private readonly ILspEditorFeatureDetector _lspEditorFeatureDetector;
+    private readonly IContentTypeRegistryService _contentTypeRegistryService = contentTypeRegistryService;
+    private readonly ILspEditorFeatureDetector _lspEditorFeatureDetector = lspEditorFeatureDetector;
+    private readonly LanguageServerFeatureOptions _options = options;
 
-    public RazorFilePathToContentTypeProviderBase(
-        IContentTypeRegistryService contentTypeRegistryService,
-        ILspEditorFeatureDetector lspEditorFeatureDetector)
+    public bool TryGetContentTypeForFilePath(string filePath, [NotNullWhen(true)] out IContentType? contentType)
     {
-        _contentTypeRegistryService = contentTypeRegistryService;
-        _lspEditorFeatureDetector = lspEditorFeatureDetector;
+        if (UseLSPEditor(filePath))
+        {
+            contentType = _contentTypeRegistryService.GetContentType(RazorConstants.RazorLSPContentTypeName);
+            return true;
+        }
+
+        contentType = null;
+        return false;
     }
 
-    public bool TryGetContentTypeForFilePath(string filePath, [NotNullWhen(true)] out IContentType? contentType)
+    private bool UseLSPEditor(string filePath)
     {
+        // When cohosting is on, it's on for all non .NET Framework projects, regardless of feature flags or
+        // project capabilities.
+        if (_options.UseRazorCohostServer &&
+            _lspEditorFeatureDetector.IsDotNetCoreProject(filePath))
+        {
+            return true;
+        }
+
+        // Otherwise, we just check for the lack of feature flag feature or project capability.
         if (_lspEditorFeatureDetector.IsLspEditorEnabled() &&
             _lspEditorFeatureDetector.IsLspEditorSupported(filePath))
         {
-            contentType = _contentTypeRegistryService.GetContentType(RazorConstants.RazorLSPContentTypeName);
             return true;
         }
 
-        contentType = null;
         return false;
     }
 }

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/LspEditorFeatureDetector.cs

@@ -103,18 +103,19 @@ public bool IsLspEditorSupported(string documentFilePath)
             return false;
         }
 
-        var supportsRazor = _projectCapabilityResolver.ResolveCapability(WellKnownProjectCapabilities.DotNetCoreCSharp, documentFilePath);
-
-        if (!supportsRazor)
+        if (!IsDotNetCoreProject(documentFilePath))
         {
             _activityLog.LogInfo($"'{documentFilePath}' does not support the LSP editor because it is not associated with the '{WellKnownProjectCapabilities.DotNetCoreCSharp}' capability.");
             return false;
         }
 
         _activityLog.LogInfo($"LSP editor is supported for '{documentFilePath}'.");
-        return supportsRazor;
+        return true;
     }
 
+    public bool IsDotNetCoreProject(string documentFilePath)
+        => _projectCapabilityResolver.ResolveCapability(WellKnownProjectCapabilities.DotNetCoreCSharp, documentFilePath);
+
     public bool IsRemoteClient()
         => _uiContextService.IsActive(Guids.LiveShareGuestUIContextGuid) ||
            _uiContextService.IsActive(VSConstants.UICONTEXT.CloudEnvironmentConnected_guid);

src/Razor/test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Cohost/CohostEndpointTest.cs

@@ -166,6 +166,7 @@ private class TestLspEditorFeatureDetector : ILspEditorFeatureDetector
         public bool IsLiveShareHost() => throw new NotImplementedException();
         public bool IsLspEditorEnabled() => throw new NotImplementedException();
         public bool IsLspEditorSupported(string documentFilePath) => throw new NotImplementedException();
+        public bool IsDotNetCoreProject(string documentFilePath) => throw new NotImplementedException();
         public bool IsRemoteClient() => throw new NotImplementedException();
     }