cancel snippet mode when undo'ing to the 'before' state, fixes #27612

src/vs/editor/contrib/snippet/browser/snippetController2.ts

@@ -82,9 +82,9 @@ export class SnippetController2 {
 	private readonly _hasNextTabstop: IContextKey<boolean>;
 	private readonly _hasPrevTabstop: IContextKey<boolean>;
 
-	// private _snippet: SnippetSession;
 	private _sessions = new SnippetSessions();
 	private _snippetListener: IDisposable[] = [];
+	private _modelVersionId: number;
 
 	constructor(
 		private readonly _editor: ICommonCodeEditor,
@@ -122,7 +122,13 @@ export class SnippetController2 {
 
 		const snippet = new SnippetSession(this._editor, template, overwriteBefore, overwriteAfter);
 		const newLen = this._sessions.add(snippet);
-		snippet.insert(newLen > 1);
+
+		if (newLen === 1) {
+			this._modelVersionId = this._editor.getModel().getAlternativeVersionId();
+			snippet.insert(false);
+		} else {
+			snippet.insert(true);
+		}
 
 		if (undoStopAfter) {
 			this._editor.getModel().pushStackElement();
@@ -141,6 +147,12 @@ export class SnippetController2 {
 			return;
 		}
 
+		if (this._modelVersionId === this._editor.getModel().getAlternativeVersionId()) {
+			// undo until the 'before' state happened
+			// and makes use cancel snippet mode
+			return this.cancel();
+		}
+
 		if (!this._sessions.hasPlaceholder) {
 			// don't listen for selection changes and don't
 			// update context keys when the snippet is plain text

src/vs/editor/contrib/snippet/test/browser/snippetController2.old.test.ts

@@ -189,16 +189,16 @@ suite('SnippetController', () => {
 		});
 	});
 
-	// test('Stops when undoing', () => {
-	// 	snippetTest((editor, cursor, codeSnippet, snippetController) => {
-	// 		editor.setPosition({ lineNumber: 4, column: 2 });
-	// 		snippetController.run(codeSnippet, 0, 0);
+	test('Stops when undoing', () => {
+		snippetTest((editor, cursor, codeSnippet, snippetController) => {
+			editor.setPosition({ lineNumber: 4, column: 2 });
+			snippetController.insert(codeSnippet, 0, 0);
 
-	// 		editor.getModel().undo();
+			editor.getModel().undo();
 
-	// 		assert.equal(snippetController.isInSnippetMode(), false);
-	// 	});
-	// });
+			assert.equal(snippetController.isInSnippetMode(), false);
+		});
+	});
 
 	test('Stops when moving cursor outside', () => {
 		snippetTest((editor, cursor, codeSnippet, snippetController) => {