fix: issue 1709 eventemitter once

packages/core/src/events/EventEmitter.test.ts

@@ -171,4 +171,79 @@ describe('EventEmitter', () => {
         expect(onceHandler).toHaveBeenCalled();
         expect(regularHandler).toHaveBeenCalled();
     });
+
+    it('re-entrant emit from regular handler does not fire once handlers early', () => {
+        const emitter = new EventEmitter<TestEvents>();
+        const log: string[] = [];
+
+        const onceHandler = vi.fn(() => { log.push('once'); });
+        const reentrant = vi.fn(() => {
+            log.push('reenter');
+            emitter.emit('message', 'inner');
+        });
+
+        emitter.on('message', reentrant);
+        emitter.once('message', onceHandler);
+
+        emitter.emit('message', 'outer');
+
+        expect(log).toEqual(['reenter', 'once']);
+        expect(onceHandler).toHaveBeenCalledTimes(1);
+    });
+
+    it('once handler registered during emit does not fire in current emit', () => {
+        const emitter = new EventEmitter<TestEvents>();
+        const log: string[] = [];
+
+        const innerOnce = vi.fn(() => { log.push('inner-once'); });
+        const outerHandler = vi.fn(() => {
+            log.push('outer');
+            emitter.once('message', innerOnce);
+        });
+
+        emitter.once('message', outerHandler);
+        emitter.emit('message', 'first');
+
+        expect(log).toEqual(['outer']);
+        expect(innerOnce).not.toHaveBeenCalled();
+
+        emitter.emit('message', 'second');
+        expect(innerOnce).toHaveBeenCalledTimes(1);
+    });
+
+    it('off removes empty Map entries for regular handlers', () => {
+        const emitter = new EventEmitter<TestEvents>();
+        const handler1 = vi.fn();
+        const handler2 = vi.fn();
+
+        emitter.on('message', handler1);
+        emitter.on('message', handler2);
+        emitter.off('message', handler1);
+        emitter.off('message', handler2);
+
+        expect(emitter.hasListeners('message')).toBe(false);
+        expect(emitter['_handlers'].has('message' as any)).toBe(false);
+    });
+
+    it('off removes empty Map entries for once handlers', () => {
+        const emitter = new EventEmitter<TestEvents>();
+        const handler = vi.fn();
+
+        emitter.once('message', handler);
+        emitter.off('message', handler);
+
+        expect(emitter.hasListeners('message')).toBe(false);
+        expect(emitter['_onceHandlers'].has('message' as any)).toBe(false);
+    });
+
+    it('emit clears OnceHandler Map entry so hasListeners returns false', () => {
+        const emitter = new EventEmitter<TestEvents>();
+        const handler = vi.fn();
+
+        emitter.once('message', handler);
+        emitter.emit('message', 'test');
+
+        expect(handler).toHaveBeenCalledTimes(1);
+        expect(emitter.hasListeners('message')).toBe(false);
+    });
 });

packages/core/src/events/EventEmitter.ts

@@ -7,8 +7,9 @@
  * Supports `on`, `off`, `once`, `emit` with type-safe event maps.
  */
 export class EventEmitter<TEventMap extends Record<string, any>> {
-    private _handlers: Map<keyof TEventMap, Set<(data: any) => void>> = new Map(); // any: handler type erased here; callers constrain via generics
-    private _onceHandlers: Map<keyof TEventMap, Set<(data: any) => void>> = new Map(); // any: handler type erased here; callers constrain via generics
+    private _handlers: Map<keyof TEventMap, Set<(data: any) => void>> = new Map();
+    private _onceHandlers: Map<keyof TEventMap, Set<(data: any) => void>> = new Map();
+    private _emitting: Set<keyof TEventMap> = new Set();
 
     /**
      * Subscribe to an event.
@@ -41,33 +42,59 @@ export class EventEmitter<TEventMap extends Record<string, any>> {
      * Unsubscribe from an event.
      */
     off<K extends keyof TEventMap>(event: K, handler: (data: TEventMap[K]) => void): void {
-        this._handlers.get(event)?.delete(handler);
-        this._onceHandlers.get(event)?.delete(handler);
+        const reg = this._handlers.get(event);
+        if (reg) {
+            reg.delete(handler);
+            if (reg.size === 0) {
+                this._handlers.delete(event);
+            }
+        }
+
+        const once = this._onceHandlers.get(event);
+        if (once) {
+            once.delete(handler);
+            if (once.size === 0) {
+                this._onceHandlers.delete(event);
+            }
+        }
     }
 
     /**
      * Emit an event to all subscribed handlers.
+     *
+     * Once handlers are removed from storage _before_ any handler executes
+     * so that re-entrant `emit()` calls on the same event cannot re-fire them.
      */
     emit<K extends keyof TEventMap>(event: K, data: TEventMap[K]): void {
-        // Regular handlers
-        const handlers = this._handlers.get(event);
-        if (handlers) {
-            for (const handler of handlers) {
-                try { handler(data); } catch (_err) {
-                    // handler errors are silently ignored to prevent crash during rendering
-                }
+        // Snap-shot and remove once handlers before firing anything
+        const onceSet = this._onceHandlers.get(event);
+        const onceSnapshot: ((data: any) => void)[] = [];
+        if (onceSet) {
+            for (const handler of onceSet) {
+                onceSnapshot.push(handler);
             }
+            this._onceHandlers.delete(event);
         }
 
-        // Once handlers — fire and remove
-        const onceHandlers = this._onceHandlers.get(event);
-        if (onceHandlers) {
-            for (const handler of onceHandlers) {
-                try { handler(data); } catch (_err) {
-                    // handler errors are silently ignored to prevent crash during rendering
+        // Regular handlers — skip if re-entrant for the same event
+        if (!this._emitting.has(event)) {
+            this._emitting.add(event);
+            const handlers = this._handlers.get(event);
+            if (handlers) {
+                for (const handler of handlers) {
+                    try { handler(data); } catch (_err) {
+                        // handler errors are silently ignored to prevent crash during rendering
+                    }
                 }
             }
-            onceHandlers.clear();
+            this._emitting.delete(event);
+        }
+
+        // Once handlers — fire removed handlers
+        for (const handler of onceSnapshot) {
+            try { handler(data); } catch (_err) {
+                // handler errors are silently ignored to prevent crash during rendering
+            }
         }
     }