Fix Backbutton is not displayed when there is a endDrawer (#101869)

Author: chunhtai

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

@@ -823,9 +823,9 @@ class _AppBarState extends State<AppBar> {
 
     final bool hasDrawer = scaffold?.hasDrawer ?? false;
     final bool hasEndDrawer = scaffold?.hasEndDrawer ?? false;
-    final bool canPop = parentRoute?.canPop ?? false;
     final bool useCloseButton = parentRoute is PageRoute<dynamic> && parentRoute.fullscreenDialog;
-
+    final bool requiresAppBarDismiss = scaffold?.requiresAppBarDismiss ?? false;
+    final bool hasActiveRouteBelow = parentRoute?.hasActiveRouteBelow ?? false;
     final double toolbarHeight = widget.toolbarHeight ?? appBarTheme.toolbarHeight ?? kToolbarHeight;
     final bool backwardsCompatibility = widget.backwardsCompatibility ?? appBarTheme.backwardsCompatibility ?? false;
 
@@ -896,7 +896,7 @@ class _AppBarState extends State<AppBar> {
           tooltip: MaterialLocalizations.of(context).openAppDrawerTooltip,
         );
       } else {
-        if (!hasEndDrawer && canPop)
+        if (hasActiveRouteBelow || requiresAppBarDismiss)
           leading = useCloseButton ? const CloseButton() : const BackButton();
       }
     }

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

@@ -1917,13 +1917,20 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
 
   /// Whether this scaffold has a non-null [Scaffold.appBar].
   bool get hasAppBar => widget.appBar != null;
+
   /// Whether this scaffold has a non-null [Scaffold.drawer].
   bool get hasDrawer => widget.drawer != null;
+
   /// Whether this scaffold has a non-null [Scaffold.endDrawer].
   bool get hasEndDrawer => widget.endDrawer != null;
+
   /// Whether this scaffold has a non-null [Scaffold.floatingActionButton].
   bool get hasFloatingActionButton => widget.floatingActionButton != null;
 
+  /// Whether this scaffold requires [Scaffold.appBar] to automatically add
+  /// dismiss button.
+  bool get requiresAppBarDismiss => _persistentSheetHistoryEntry != null;
+
   double? _appBarMaxHeight;
   /// The max height the [Scaffold.appBar] uses.
   ///
@@ -2051,28 +2058,28 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
   PersistentBottomSheetController<dynamic>? _currentBottomSheet;
   final GlobalKey _currentBottomSheetKey = GlobalKey();
 
+  LocalHistoryEntry? _persistentSheetHistoryEntry;
   void _maybeBuildPersistentBottomSheet() {
     if (widget.bottomSheet != null && _currentBottomSheet == null) {
       // The new _currentBottomSheet is not a local history entry so a "back" button
       // will not be added to the Scaffold's appbar and the bottom sheet will not
       // support drag or swipe to dismiss.
       final AnimationController animationController = BottomSheet.createAnimationController(this)..value = 1.0;
-      LocalHistoryEntry? persistentSheetHistoryEntry;
       bool _persistentBottomSheetExtentChanged(DraggableScrollableNotification notification) {
         if (notification.extent > notification.initialExtent) {
-          if (persistentSheetHistoryEntry == null) {
-            persistentSheetHistoryEntry = LocalHistoryEntry(onRemove: () {
+          if (_persistentSheetHistoryEntry == null) {
+            _persistentSheetHistoryEntry = LocalHistoryEntry(onRemove: () {
               if (notification.extent > notification.initialExtent) {
                 DraggableScrollableActuator.reset(notification.context);
               }
               showBodyScrim(false, 0.0);
               _floatingActionButtonVisibilityValue = 1.0;
-              persistentSheetHistoryEntry = null;
+              _persistentSheetHistoryEntry = null;
             });
-            ModalRoute.of(context)!.addLocalHistoryEntry(persistentSheetHistoryEntry!);
+            ModalRoute.of(context)!.addLocalHistoryEntry(_persistentSheetHistoryEntry!);
           }
-        } else if (persistentSheetHistoryEntry != null) {
-          ModalRoute.of(context)!.removeLocalHistoryEntry(persistentSheetHistoryEntry!);
+        } else if (_persistentSheetHistoryEntry != null) {
+          ModalRoute.of(context)!.removeLocalHistoryEntry(_persistentSheetHistoryEntry!);
         }
         return false;
       }

packages/flutter/lib/src/widgets/navigator.dart

@@ -486,7 +486,6 @@ abstract class Route<T> {
   }
 
   /// Whether there is at least one active route underneath this route.
-  @protected
   bool get hasActiveRouteBelow {
     if (_navigator == null)
       return false;

packages/flutter/test/material/app_bar_test.dart

@@ -2873,6 +2873,44 @@ void main() {
         expect(tester.getSize(findAppBarMaterial()).height, kToolbarHeight);
       });
 
+      // Regression test for https://github.com/flutter/flutter/issues/80256
+      testWidgets('The second page should have a back button even it has a end drawer', (WidgetTester tester) async {
+        final Page<void> page1 = MaterialPage<void>(
+            key: const ValueKey<String>('1'),
+            child: Scaffold(
+              key: const ValueKey<String>('1'),
+              appBar: AppBar(),
+              endDrawer: const Drawer(),
+            )
+        );
+        final Page<void> page2 = MaterialPage<void>(
+            key: const ValueKey<String>('2'),
+            child: Scaffold(
+              key: const ValueKey<String>('2'),
+              appBar: AppBar(),
+              endDrawer: const Drawer(),
+            )
+        );
+        final List<Page<void>> pages = <Page<void>>[ page1, page2 ];
+        await tester.pumpWidget(
+          MaterialApp(
+            home: Navigator(
+              pages: pages,
+              onPopPage: (Route<Object?> route, Object? result) => false,
+            ),
+          ),
+        );
+
+        // The page2 should have a back button.
+        expect(
+            find.descendant(
+              of: find.byKey(const ValueKey<String>('2')),
+              matching: find.byType(BackButton),
+            ),
+            findsOneWidget
+        );
+      });
+
       testWidgets('backgroundColor with FlexibleSpace - reverse', (WidgetTester tester) async {
         await tester.pumpWidget(
           _buildAppBar(