Send document buffer when semantically highlighting old document vers…

…ions

package.json

@@ -724,7 +724,7 @@
         },
         "csharp.semanticHighlighting.enabled": {
           "type": "boolean",
-          "default": false,
+          "default": true,
           "description": "Enable/disable Semantic Highlighting for C# files (Razor files currently unsupported). Defaults to false. Close open files for changes to take effect.",
           "scope": "window"
         },
@@ -3820,4 +3820,4 @@
       }
     ]
   }
-}
+}

src/features/semanticTokensProvider.ts

@@ -187,7 +187,11 @@ export default class SemanticTokensProvider extends AbstractProvider implements
             return null;
         }
 
-        let req = createRequest<protocol.V2.SemanticHighlightRequest>(document, new vscode.Position(0, 0));
+        const currentDocument = vscode.workspace.textDocuments.find(d => d.fileName === document.fileName);
+        const isCurrentVersion = currentDocument?.version === document.version;
+
+        // We need to include the document contents in our request when we are highlighting a version of the document other than the current version, such as in the Diff view.
+        let req = createRequest<protocol.V2.SemanticHighlightRequest>(document, new vscode.Position(0, 0), /* includeBuffer: */ !isCurrentVersion);
         req.Range = range;
 
         const versionBeforeRequest = document.version;