fix(ui): show a snackbar queued before its host mounts

packages/stream_core_flutter/CHANGELOG.md

@@ -4,6 +4,9 @@
 
 - Fixed `StreamTextInput` ignoring typed text after the widgets around it, such
   as `leading` and `trailing`, changed while it had focus.
+- Fixed `StreamSnackbarHost` and `StreamSnackbarPopup` throwing in debug when
+  they mount with a snackbar already queued on their messenger, for example
+  after the widget holding them is rebuilt.
 
 ## 0.5.3
 

packages/stream_core_flutter/lib/src/components/snackbar/stream_snackbar_messenger.dart

@@ -734,6 +734,12 @@ class _SnackbarStageState extends State<_SnackbarStage> with SingleTickerProvide
 
   void _onControllerChanged() => _syncWithController();
 
+  // No dependency on MediaQuery: the first read can come from initState.
+  bool get _accessibleNavigation {
+    final mediaQuery = context.getInheritedWidgetOfExactType<MediaQuery>();
+    return mediaQuery?.data.accessibleNavigation ?? false;
+  }
+
   void _syncWithController() {
     final next = widget.messenger._queue.isEmpty ? null : widget.messenger._queue.first;
 
@@ -756,7 +762,7 @@ class _SnackbarStageState extends State<_SnackbarStage> with SingleTickerProvide
     _animation.value = 0;
     setState(() {});
     if (next != null) {
-      if (MediaQuery.accessibleNavigationOf(context)) {
+      if (_accessibleNavigation) {
         _animation.value = 1;
       } else {
         _animation.forward(from: 0);
@@ -786,7 +792,7 @@ class _SnackbarStageState extends State<_SnackbarStage> with SingleTickerProvide
     final messenger = widget.messenger;
     _exiting = true;
     _timer?.cancel();
-    if (MediaQuery.accessibleNavigationOf(context)) {
+    if (_accessibleNavigation) {
       _animation.value = 0;
     } else {
       await _animation.reverse();

packages/stream_core_flutter/test/components/snackbar/stream_snackbar_test.dart

@@ -848,6 +848,29 @@ void main() {
 
       expect(find.text('Auto-managed'), findsOneWidget);
     });
+
+    testWidgets('shows a snackbar queued before it mounts', (tester) async {
+      final messenger = StreamSnackbarMessenger();
+      addTearDown(messenger.dispose);
+
+      messenger.show(StreamSnackbar(message: const Text('Queued')));
+
+      await tester.pumpWidget(
+        MaterialApp(
+          theme: ThemeData(extensions: [StreamTheme.light()]),
+          home: Center(
+            child: StreamSnackbarPopup.withState(
+              messenger: messenger,
+              child: const SizedBox(width: 200, height: 60),
+            ),
+          ),
+        ),
+      );
+      await tester.pump(const Duration(milliseconds: 300));
+
+      expect(tester.takeException(), isNull);
+      expect(find.text('Queued'), findsOneWidget);
+    });
   });
 
   group('accessibleNavigation', () {
@@ -893,6 +916,22 @@ void main() {
       expect(fadeOf(tester).opacity.value, equals(1.0));
     });
 
+    testWidgets('on — a snackbar queued before the host mounts skips animation', (tester) async {
+      tester.platformDispatcher.accessibilityFeaturesTestValue = const FakeAccessibilityFeatures(
+        accessibleNavigation: true,
+      );
+      addTearDown(tester.platformDispatcher.clearAccessibilityFeaturesTestValue);
+
+      final messenger = StreamSnackbarMessenger();
+      addTearDown(messenger.dispose);
+
+      messenger.show(StreamSnackbar(message: const Text('Queued')));
+      await tester.pumpWidget(hostScaffold(messenger));
+
+      expect(tester.takeException(), isNull);
+      expect(fadeOf(tester).opacity.value, equals(1.0));
+    });
+
     testWidgets('on — exit skips animation and resolves controller after one frame', (tester) async {
       tester.platformDispatcher.accessibilityFeaturesTestValue = const FakeAccessibilityFeatures(
         accessibleNavigation: true,