Toggle enable-mouse-events cursor while alt is held for mouseEventsRequireAlt.

Extract AltMouseCursorController to bind DOM listeners only when the option and mouse protocol are active.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/browser/services/MouseService.ts

@@ -7,7 +7,7 @@ import { addDisposableListener } from 'browser/Dom';
 import { IBufferService, IMouseStateService, ICoreService, ILogService, IOptionsService } from 'common/services/Services';
 import { CoreMouseAction, CoreMouseButton, CoreMouseEventType, ICoreMouseEvent, IDisposable } from 'common/Types';
 import { C0 } from 'common/data/EscapeSequences';
-import { toDisposable } from 'common/Lifecycle';
+import { DisposableStore, MutableDisposable, toDisposable } from 'common/Lifecycle';
 import { ICoreBrowserService, IMouseCoordsService, IMouseService, IMouseServiceTarget, IRenderService, ISelectionService } from './Services';
 import { Gesture, EventType as GestureEventType, IGestureEvent } from 'browser/scrollable/touch';
 
@@ -25,6 +25,7 @@ export class MouseService implements IMouseService {
   private _lastEvent: ICoreMouseEvent | null = null;
   private _wheelPartialScroll: number = 0;
   private _touchScrollAccumulator: number = 0;
+  private _altMouseCursor: AltMouseCursorController | undefined;
 
   constructor(
     @IRenderService private readonly _renderService: IRenderService,
@@ -63,11 +64,19 @@ export class MouseService implements IMouseService {
       mousedrag: (ev: Event) => this._handleMouseDrag(ctx, ev as MouseEvent),
       mousemove: (ev: Event) => this._handleMouseMove(ctx, ev as MouseEvent)
     };
+    this._altMouseCursor = new AltMouseCursorController(
+      element,
+      document,
+      () => this._mouseStateService.areMouseEventsActive
+        && !!this._optionsService.rawOptions.mouseEventsRequireAlt
+    );
+    register(this._altMouseCursor);
     register(this._mouseStateService.onProtocolChange(events => {
       this._handleProtocolChange(ctx, eventListeners, events);
     }));
     register(this._optionsService.onSpecificOptionChange('mouseEventsRequireAlt', () => {
       this._syncMouseModeState(element);
+      this._altMouseCursor?.sync();
     }));
     // force initial onProtocolChange so we dont miss early mouse requests
     this._mouseStateService.activeProtocol = this._mouseStateService.activeProtocol;
@@ -372,7 +381,7 @@ export class MouseService implements IMouseService {
   private _syncMouseModeState(element: HTMLElement): void {
     if (this._mouseStateService.areMouseEventsActive) {
       if (this._optionsService.rawOptions.mouseEventsRequireAlt) {
-        element.classList.remove('enable-mouse-events');
+        this._altMouseCursor?.resetClass();
         this._selectionService.enable();
       } else {
         element.classList.add('enable-mouse-events');
@@ -396,6 +405,7 @@ export class MouseService implements IMouseService {
       this._logService.debug('Unbinding from mouse events.');
     }
     this._syncMouseModeState(element);
+    this._altMouseCursor?.sync();
 
     // add/remove handlers from requestedEvents
     if (!(events & CoreMouseEventType.MOVE)) {
@@ -565,3 +575,64 @@ export class MouseService implements IMouseService {
   }
 
 }
+
+/**
+ * Toggles `enable-mouse-events` on the terminal element while alt is held when
+ * `mouseEventsRequireAlt` is active. DOM listeners are only registered while active.
+ */
+export class AltMouseCursorController implements IDisposable {
+  private readonly _listeners = new MutableDisposable<IDisposable>();
+
+  constructor(
+    private readonly _element: HTMLElement,
+    private readonly _document: Document,
+    private readonly _isActive: () => boolean
+  ) {
+  }
+
+  public dispose(): void {
+    this._listeners.dispose();
+  }
+
+  public sync(): void {
+    this._listeners.clear();
+
+    if (!this._isActive()) {
+      return;
+    }
+
+    const store = new DisposableStore();
+    const syncFromModifier = (ev: KeyboardEvent | MouseEvent) => this.syncFromModifier(ev);
+    store.add(addDisposableListener(this._document, 'keydown', syncFromModifier));
+    store.add(addDisposableListener(this._document, 'keyup', syncFromModifier));
+    store.add(addDisposableListener(this._element, 'mousemove', syncFromModifier));
+    const targetWindow = this._element.ownerDocument?.defaultView;
+    if (targetWindow) {
+      store.add(addDisposableListener(targetWindow, 'blur', () => {
+        if (this._isActive()) {
+          this.resetClass();
+        }
+      }));
+    }
+    this._listeners.value = store;
+  }
+
+  public resetClass(): void {
+    this._updateClass(false);
+  }
+
+  public syncFromModifier(ev: KeyboardEvent | MouseEvent): void {
+    if (!this._isActive()) {
+      return;
+    }
+    this._updateClass(ev.getModifierState('Alt'));
+  }
+
+  private _updateClass(altHeld: boolean): void {
+    if (altHeld) {
+      this._element.classList.add('enable-mouse-events');
+    } else {
+      this._element.classList.remove('enable-mouse-events');
+    }
+  }
+}