Re-rework LspEditorFeatureDetector

My previous work on LspEditorFeatureDetector introduced a significant regression by removing the code that checked project capabilities. When a razor document is opened, the LspEditorFeatureDetector is queried to see if the LSP editor is enabled (i.e. the user hasn't enabled the legacy editor instead), and to see whether the project that the document belongs to supports the LSP editor. In the case of .NET Framework projects, the LSP editor can't ever be used, and my prior change broke that. (Many thanks to @alexgav for fixing my mistake!)

Giving the situation a bit more thought, I've reworked LspEditorFeatureDetector again to simplify the code and fix a different issue where we would start checking project capabilities where we hadn't before.

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/DynamicFiles/RazorDynamicFileInfoProvider.cs

@@ -201,7 +201,7 @@ public void SuppressDocument(ProjectKey projectKey, string documentFilePath)
             throw new ArgumentNullException(nameof(documentFilePath));
         }
 
-        if (_lspEditorFeatureDetector.IsLspEditorEnabledAndAvailable(documentFilePath))
+        if (_lspEditorFeatureDetector.IsLspEditorEnabled())
         {
             return;
         }

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

@@ -5,7 +5,16 @@ namespace Microsoft.VisualStudio.Razor;
 
 internal interface ILspEditorFeatureDetector
 {
-    bool IsLspEditorEnabledAndAvailable(string documentFilePath);
+    /// <summary>
+    /// Determines whether the LSP editor is enabled. This returns <see langword="true"/>
+    /// if the legacy editor has <i>not</i> been enabled via the feature flag or tools/options.
+    /// </summary>
+    bool IsLspEditorEnabled();
+
+    /// <summary>
+    /// Determines whether the LSP editor is supported by the given document.
+    /// </summary>
+    bool IsLspEditorSupported(string documentFilePath);
 
     /// <summary>
     /// A remote client is a LiveShare guest or a Codespaces instance

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

@@ -5,5 +5,8 @@ namespace Microsoft.VisualStudio.Razor;
 
 internal interface IProjectCapabilityResolver
 {
-    bool HasCapability(string documentFilePath, object project, string capability);
+    /// <summary>
+    /// Determines whether the project associated with the specified document has the given <paramref name="capability"/>.
+    /// </summary>
+    bool ResolveCapability(string capability, string documentFilePath);
 }

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

@@ -9,12 +9,10 @@ namespace Microsoft.VisualStudio.Razor.LanguageClient;
 [FileExtension(RazorLSPConstants.CSHTMLFileExtension)]
 [Name(nameof(CSHTMLFilePathToContentTypeProvider))]
 [Export(typeof(IFilePathToContentTypeProvider))]
-internal class CSHTMLFilePathToContentTypeProvider : RazorFilePathToContentTypeProviderBase
+[method: ImportingConstructor]
+internal class CSHTMLFilePathToContentTypeProvider(
+    IContentTypeRegistryService contentTypeRegistryService,
+    ILspEditorFeatureDetector lspEditorFeatureDetector)
+    : RazorFilePathToContentTypeProviderBase(contentTypeRegistryService, lspEditorFeatureDetector)
 {
-    [ImportingConstructor]
-    public CSHTMLFilePathToContentTypeProvider(
-        IContentTypeRegistryService contentTypeRegistryService,
-        ILspEditorFeatureDetector lspEditorFeatureDetector) : base(contentTypeRegistryService, lspEditorFeatureDetector)
-    {
-    }
 }

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

@@ -9,12 +9,10 @@ namespace Microsoft.VisualStudio.Razor.LanguageClient;
 [FileExtension(RazorLSPConstants.RazorFileExtension)]
 [Name(nameof(RazorFilePathToContentTypeProvider))]
 [Export(typeof(IFilePathToContentTypeProvider))]
-internal class RazorFilePathToContentTypeProvider : RazorFilePathToContentTypeProviderBase
+[method: ImportingConstructor]
+internal class RazorFilePathToContentTypeProvider(
+    IContentTypeRegistryService contentTypeRegistryService,
+    ILspEditorFeatureDetector lspEditorFeatureDetector)
+    : RazorFilePathToContentTypeProviderBase(contentTypeRegistryService, lspEditorFeatureDetector)
 {
-    [ImportingConstructor]
-    public RazorFilePathToContentTypeProvider(
-        IContentTypeRegistryService contentTypeRegistryService,
-        ILspEditorFeatureDetector lspEditorFeatureDetector) : base(contentTypeRegistryService, lspEditorFeatureDetector)
-    {
-    }
 }

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

@@ -1,7 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
-using System;
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.VisualStudio.Utilities;
 
@@ -16,23 +15,14 @@ public RazorFilePathToContentTypeProviderBase(
         IContentTypeRegistryService contentTypeRegistryService,
         ILspEditorFeatureDetector lspEditorFeatureDetector)
     {
-        if (contentTypeRegistryService is null)
-        {
-            throw new ArgumentNullException(nameof(contentTypeRegistryService));
-        }
-
-        if (lspEditorFeatureDetector is null)
-        {
-            throw new ArgumentNullException(nameof(lspEditorFeatureDetector));
-        }
-
         _contentTypeRegistryService = contentTypeRegistryService;
         _lspEditorFeatureDetector = lspEditorFeatureDetector;
     }
 
     public bool TryGetContentTypeForFilePath(string filePath, [NotNullWhen(true)] out IContentType? contentType)
     {
-        if (_lspEditorFeatureDetector.IsLspEditorEnabledAndAvailable(filePath))
+        if (_lspEditorFeatureDetector.IsLspEditorEnabled() &&
+            _lspEditorFeatureDetector.IsLspEditorSupported(filePath))
         {
             contentType = _contentTypeRegistryService.GetContentType(RazorConstants.RazorLSPContentTypeName);
             return true;

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/LiveShare/Guest/ILiveShareSessionAccessor.cs

@@ -1,12 +1,15 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
+using System.Diagnostics.CodeAnalysis;
 using Microsoft.VisualStudio.LiveShare;
 
 namespace Microsoft.VisualStudio.Razor.LiveShare.Guest;
 
 internal interface ILiveShareSessionAccessor
 {
     CollaborationSession? Session { get; }
+
+    [MemberNotNullWhen(true, nameof(Session))]
     bool IsGuestSessionActive { get; }
 }