More gracefully handle license loading failures (#87841)

Author: Hixie

packages/flutter/lib/src/material/about.dart

@@ -571,6 +571,17 @@ class _PackagesViewState extends State<_PackagesView> {
           builder: (BuildContext context, BoxConstraints constraints) {
             switch (snapshot.connectionState) {
               case ConnectionState.done:
+                if (snapshot.hasError) {
+                  assert(() {
+                    FlutterError.reportError(FlutterErrorDetails(
+                      exception: snapshot.error!,
+                      stack: snapshot.stackTrace,
+                      context: ErrorDescription('while decoding the license file'),
+                    ));
+                    return true;
+                  }());
+                  return Center(child: Text(snapshot.error.toString()));
+                }
                 _initDefaultDetailPage(snapshot.data!, context);
                 return ValueListenableBuilder<int?>(
                   valueListenable: widget.selectedId,

packages/flutter/test/material/about_test.dart

@@ -997,6 +997,24 @@ void main() {
     final double appIconBottomPadding = tester.getTopLeft(appPowered).dy - tester.getBottomLeft(appIcon).dy;
     expect(appIconBottomPadding, 18.0);
   });
+
+  testWidgets('Error handling test', (WidgetTester tester) async {
+    LicenseRegistry.addLicense(() => Stream<LicenseEntry>.error(Exception('Injected failure')));
+    await tester.pumpWidget(const MaterialApp(home: Material(child: AboutListTile())));
+    await tester.tap(find.byType(ListTile));
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 2));
+    await tester.tap(find.text('VIEW LICENSES'));
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 2));
+    final Finder finder = find.byWidgetPredicate((Widget widget) => widget.runtimeType.toString() == '_PackagesView');
+    // force the stream to complete (has to be done in a runAsync block since it's areal async process)
+    await tester.runAsync(() => (tester.firstState(finder) as dynamic).licenses as Future<dynamic>); // ignore: avoid_dynamic_calls
+    expect(tester.takeException().toString(), 'Exception: Injected failure');
+    await tester.pumpAndSettle();
+    expect(tester.takeException().toString(), 'Exception: Injected failure');
+    expect(find.text('Exception: Injected failure'), findsOneWidget);
+  });
 }
 
 class FakeLicenseEntry extends LicenseEntry {