Fixes #89552: Throw from the provider when semantic tokens cannot be computed...

Fixes #89552: Throw from the provider when semantic tokens cannot be computed and keep old semantic tokens if this happens

extensions/typescript-language-features/src/features/semanticTokens.ts

@@ -80,7 +80,11 @@ class DocumentSemanticTokensProvider implements vscode.DocumentSemanticTokensPro
 		if (versionBeforeRequest !== versionAfterRequest) {
 			// cannot convert result's offsets to (line;col) values correctly
 			// a new request will come in soon...
-			return null;
+			//
+			// here we cannot return null, because returning null would remove all semantic tokens.
+			// we must throw to indicate that the semantic tokens should not be removed.
+			// using the string busy here because it is not logged to error telemetry if the error text contains busy.
+			throw new Error('busy');
 		}
 
 		const tokenSpan = response.body.spans;

src/vs/editor/common/services/modelServiceImpl.ts

@@ -785,10 +785,21 @@ class ModelSemanticColoring extends Disposable {
 			contentChangeListener.dispose();
 			this._setSemanticTokens(provider, res || null, styling, pendingChanges);
 		}, (err) => {
-			errors.onUnexpectedError(err);
+			if (!err || typeof err.message !== 'string' || err.message.indexOf('busy') === -1) {
+				errors.onUnexpectedError(err);
+			}
+
+			// Semantic tokens eats up all errors and considers errors to mean that the result is temporarily not available
+			// The API does not have a special error kind to express this...
 			this._currentRequestCancellationTokenSource = null;
 			contentChangeListener.dispose();
-			this._setSemanticTokens(provider, null, styling, pendingChanges);
+
+			if (pendingChanges.length > 0) {
+				// More changes occurred while the request was running
+				if (!this._fetchSemanticTokens.isScheduled()) {
+					this._fetchSemanticTokens.schedule();
+				}
+			}
 		});
 	}