fix(Snackbar): apply hidden state when animation reports finished:false under Fabric

src/components/Snackbar.tsx

@@ -199,14 +199,17 @@ const Snackbar = ({
       clearTimeout(hideTimeout.current);
     }
 
+    // Under the New Architecture (Fabric), the animation callback can fire
+    // with `finished: false` even when the animation completes naturally.
+    // Guarding `setHidden(true)` on `finished` causes the Snackbar to stay
+    // mounted after `visible` becomes false on Fabric (issue #4951).
+    // Mirror the show-path fix from PR #4447: call setHidden unconditionally.
     Animated.timing(opacity, {
       toValue: 0,
       duration: 100 * scale,
       useNativeDriver: true,
-    }).start(({ finished }) => {
-      if (finished) {
-        setHidden(true);
-      }
+    }).start(() => {
+      setHidden(true);
     });
   });
 

src/components/__tests__/Snackbar.test.tsx

@@ -93,6 +93,66 @@ it('renders snackbar with View & Text as a child', async () => {
   expect(tree).toMatchSnapshot();
 });
 
+// Regression test for https://github.com/callstack/react-native-paper/issues/4951
+// Under the New Architecture (Fabric), Animated.timing fires its callback with
+// `finished: false` even when the animation completes naturally.  The hide path
+// in handleOnHidden gated `setHidden(true)` on `if (finished)`, so the Snackbar
+// stayed mounted forever.  The fix removes that guard (mirrors the show-path fix
+// from PR #4447).
+it('unmounts after visible becomes false even when the hide animation reports finished:false (Fabric new arch)', async () => {
+  // Arrange: mount visible Snackbar and settle the show animation.
+  const view = await render(
+    <Snackbar visible onDismiss={jest.fn()} testID="snack-bar">
+      Snackbar content
+    </Snackbar>
+  );
+
+  await act(() => {
+    jest.advanceTimersByTime(300); // > 200 ms show animation
+  });
+
+  // Confirm the component is currently rendered.
+  expect(view.toJSON()).not.toBeNull();
+
+  // Override Animated.timing for the single hide-animation call to simulate
+  // Fabric's behaviour: the animation plays to completion visually but the
+  // callback receives { finished: false }.
+  jest.spyOn(Animated, 'timing').mockImplementationOnce((value, config) => ({
+    start: (callback?: Animated.EndCallback) => {
+      setTimeout(() => {
+        (value as Animated.Value).setValue(config.toValue as number);
+        // Fabric new-arch bug: reports finished:false on a completed animation.
+        callback?.({ finished: false });
+      }, 0);
+    },
+    stop: () => {},
+    reset: () => {},
+  }));
+
+  // Act: flip visible to false, which triggers handleOnHidden → the mocked
+  // Animated.timing call → schedules the callback with { finished: false }.
+  // rerender is async in @testing-library/react-native v14 and must be awaited
+  // so useLayoutEffect runs and Animated.timing is called before the spy is gone.
+  await view.rerender(
+    <Snackbar visible={false} onDismiss={jest.fn()} testID="snack-bar">
+      Snackbar content
+    </Snackbar>
+  );
+
+  // Fire the hide-animation callback, then flush the microtask queue so that
+  // React 19's concurrent scheduler can apply the setHidden(true) state update.
+  await act(async () => {
+    jest.advanceTimersByTime(200);
+    await Promise.resolve();
+  });
+
+  jest.restoreAllMocks();
+
+  // Assert: setHidden(true) must have been called unconditionally so the
+  // component returns null and unmounts, regardless of the finished flag.
+  expect(view.toJSON()).toBeNull();
+});
+
 it('animated value changes correctly', async () => {
   const value = new Animated.Value(1);
   await render(