src/Tools/VSCode/no_extension/src/extension.ts

+'use strict';
+
+import { ExtensionContext, window } from 'vscode'
+
+export function activate(context: ExtensionContext)
+{
+  window.showErrorMessage("Obsolete extension: use bundled Isabelle/VSCode from the Isabelle distribution")
+}
+
+export function deactivate() { }