Have TentativeBoundary trigger rollback (#112510)

* have TentativeBoundary trigger rollback

* add test

* simplify test

* add additional test

src/vs/workbench/contrib/terminal/browser/terminalTypeAheadAddon.ts

@@ -330,7 +330,8 @@ class TentativeBoundary implements IPrediction {
 		return '';
 	}
 
-	public rollback() {
+	public rollback(cursor: Cursor) {
+		this.inner.rollback(cursor);
 		return '';
 	}
 

src/vs/workbench/contrib/terminal/test/browser/terminalTypeahead.test.ts

@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as assert from 'assert';
-import { Terminal } from 'xterm';
+import { IBuffer, Terminal } from 'xterm';
 import { SinonStub, stub, useFakeTimers } from 'sinon';
 import { Emitter } from 'vs/base/common/event';
 import { CharPredictState, IPrediction, PredictionStats, TypeAheadAddon } from 'vs/workbench/contrib/terminal/browser/terminalTypeAheadAddon';
@@ -14,6 +14,11 @@ import { ITelemetryService } from 'vs/platform/telemetry/common/telemetry';
 
 const CSI = `\x1b[`;
 
+const enum CursorMoveDirection {
+	Back = 'D',
+	Forwards = 'C',
+}
+
 suite('Workbench - Terminal Typeahead', () => {
 	suite('PredictionStats', () => {
 		let stats: PredictionStats;
@@ -139,6 +144,42 @@ suite('Workbench - Terminal Typeahead', () => {
 			assert.strictEqual(addon.stats?.accuracy, 0);
 		});
 
+		test('handles left arrow when we hit the boundary', () => {
+			const t = createMockTerminal({ lines: ['|'] });
+			addon.activate(t.terminal);
+			addon.unlockLeftNavigating();
+
+			const cursorXBefore = addon.getCursor(t.terminal.buffer.active)?.x!;
+			t.onData(`${CSI}${CursorMoveDirection.Back}`);
+			t.expectWritten('');
+
+			// Trigger rollback because we don't expect this data
+			onBeforeProcessData.fire({ data: 'xy' });
+
+			assert.strictEqual(
+				addon.getCursor(t.terminal.buffer.active)?.x,
+				// The cursor should not have changed because we've hit the
+				// boundary (start of prompt)
+				cursorXBefore);
+		});
+
+		test('internal cursor state is reset when all predictions are undone', () => {
+			const t = createMockTerminal({ lines: ['|'] });
+			addon.activate(t.terminal);
+			addon.unlockLeftNavigating();
+
+			const cursorXBefore = addon.getCursor(t.terminal.buffer.active)?.x!;
+			t.onData(`${CSI}${CursorMoveDirection.Back}`);
+			t.expectWritten('');
+			addon.undoAllPredictions();
+
+			assert.strictEqual(
+				addon.getCursor(t.terminal.buffer.active)?.x,
+				// The cursor should not have changed because we've hit the
+				// boundary (start of prompt)
+				cursorXBefore);
+		});
+
 		test('restores cursor graphics mode', () => {
 			const t = createMockTerminal({
 				lines: ['hello|'],
@@ -296,6 +337,14 @@ class TestTypeAheadAddon extends TypeAheadAddon {
 	public get isShowing() {
 		return !!this.timeline?.isShowingPredictions;
 	}
+
+	public undoAllPredictions() {
+		this.timeline?.undoAllPredictions();
+	}
+
+	public getCursor(buffer: IBuffer) {
+		return this.timeline?.getCursor(buffer);
+	}
 }
 
 function upcastPartial<T>(v: Partial<T>): T {