From 81bd671906321a77a0b75e7d846f96847a1f5d4e Mon Sep 17 00:00:00 2001
From: Jessica Janiuk <jessica.janiuk@gmail.com>
Date: Wed, 22 Oct 2025 11:30:28 -0700
Subject: [PATCH] fix(core): prevent duplicate nodes from being retained with
 fast `animate.leave`` calls (#64592)

We were clearing duplicate nodes when `animate.enter` fired fast, but not when solely `animate.leave` is fired and rapid toggles occur. This ensures that the `cancelLeavingNodes` function is called in all cases instead of just enter animations.

fixes: #64581

PR Close #64592
---
 .../src/render3/instructions/animation.ts     |  5 +-
 .../core/test/acceptance/animation_spec.ts    | 51 +++++++++++++++++++
 2 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/packages/core/src/render3/instructions/animation.ts b/packages/core/src/render3/instructions/animation.ts
index 14e3ed7656e..5b34015fa84 100644
--- a/packages/core/src/render3/instructions/animation.ts
+++ b/packages/core/src/render3/instructions/animation.ts
@@ -68,7 +68,6 @@ export function ɵɵanimateEnter(value: string | Function): typeof ɵɵanimateEn
   }
 
   const tNode = getCurrentTNode()!;
-
   cancelLeavingNodes(tNode, lView);
 
   addAnimationToLView(getLViewEnterAnimations(lView), tNode, () =>
@@ -196,7 +195,6 @@ export function ɵɵanimateEnterListener(value: AnimationFunction): typeof ɵɵa
     return ɵɵanimateEnterListener;
   }
   const tNode = getCurrentTNode()!;
-
   cancelLeavingNodes(tNode, lView);
 
   addAnimationToLView(getLViewEnterAnimations(lView), tNode, () =>
@@ -251,6 +249,7 @@ export function ɵɵanimateLeave(value: string | Function): typeof ɵɵanimateLe
   }
 
   const tNode = getCurrentTNode()!;
+  cancelLeavingNodes(tNode, lView);
 
   addAnimationToLView(getLViewLeaveAnimations(lView), tNode, () =>
     runLeaveAnimations(lView, tNode, value),
@@ -383,6 +382,8 @@ export function ɵɵanimateLeaveListener(value: AnimationFunction): typeof ɵɵa
 
   const lView = getLView();
   const tNode = getCurrentTNode()!;
+  cancelLeavingNodes(tNode, lView);
+
   allLeavingAnimations.add(lView);
 
   addAnimationToLView(getLViewLeaveAnimations(lView), tNode, () =>
diff --git a/packages/core/test/acceptance/animation_spec.ts b/packages/core/test/acceptance/animation_spec.ts
index 9faa29cc46b..d6592d8c221 100644
--- a/packages/core/test/acceptance/animation_spec.ts
+++ b/packages/core/test/acceptance/animation_spec.ts
@@ -12,10 +12,12 @@ import {
   AfterViewInit,
   AnimationCallbackEvent,
   ChangeDetectionStrategy,
+  ChangeDetectorRef,
   Component,
   computed,
   Directive,
   ElementRef,
+  inject,
   NgModule,
   OnDestroy,
   provideZonelessChangeDetection,
@@ -1627,6 +1629,55 @@ describe('Animation', () => {
       expect(paragraphs.length).toBe(1);
     }));
 
+    it('should reset leave animation and not duplicate node when toggled programmatically very quickly', fakeAsync(() => {
+      const animateStyles = `
+        .fade {
+          animation: fade-out 500ms;
+        }
+        @keyframes fade-out {
+          from {
+            opacity: 1;
+          }
+          to {
+            opacity: 0;
+          }
+        }
+      `;
+
+      @Component({
+        selector: 'test-cmp',
+        styles: animateStyles,
+        template: '<div>@if (show()) {<p animate.leave="fade">I should fade</p>}</div>',
+        encapsulation: ViewEncapsulation.None,
+      })
+      class TestComponent {
+        show = signal(false);
+        cdr = inject(ChangeDetectorRef);
+
+        toggle() {
+          this.show.update((s) => !s);
+          setTimeout(() => {
+            this.show.update((s) => !s);
+            this.cdr.detectChanges();
+
+            setTimeout(() => {
+              this.show.update((s) => !s);
+              this.cdr.detectChanges();
+            });
+          });
+        }
+      }
+      TestBed.configureTestingModule({animationsEnabled: true});
+
+      const fixture = TestBed.createComponent(TestComponent);
+      const cmp = fixture.componentInstance;
+      cmp.toggle();
+      fixture.detectChanges();
+      tickAnimationFrames(1);
+      const paragraphs = fixture.debugElement.queryAll(By.css('p'));
+      expect(paragraphs.length).toBe(1);
+    }));
+
     it('should always run animations for `@for` loops when adding and removing quickly', fakeAsync(() => {
       const animateStyles = `
         .slide-in {