Update Navigator updatePages() (#116945)

* Update navigator.dart

* Update navigator.dart

* Add test

* Update navigator.dart

* lint

* Update packages/flutter/test/widgets/navigator_test.dart

Co-authored-by: chunhtai <47866232+chunhtai@users.noreply.github.com>

* Update packages/flutter/test/widgets/navigator_test.dart

Co-authored-by: chunhtai <47866232+chunhtai@users.noreply.github.com>

Co-authored-by: chunhtai <47866232+chunhtai@users.noreply.github.com>

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

@@ -3687,15 +3687,14 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
       oldEntriesBottom += 1;
     }
 
-    int pagelessRoutesToSkip = 0;
+    final List<_RouteEntry> unattachedPagelessRoutes=<_RouteEntry>[];
     // Scans the top of the list until we found a page-based route that cannot be
     // updated.
     while ((oldEntriesBottom <= oldEntriesTop) && (newPagesBottom <= newPagesTop)) {
       final _RouteEntry oldEntry = _history[oldEntriesTop];
       assert(oldEntry != null && oldEntry.currentState != _RouteLifecycle.disposed);
       if (!oldEntry.pageBased) {
-        // This route might need to be skipped if we can not find a page above.
-        pagelessRoutesToSkip += 1;
+        unattachedPagelessRoutes.add(oldEntry);
         oldEntriesTop -= 1;
         continue;
       }
@@ -3703,14 +3702,22 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin, Res
       if (!oldEntry.canUpdateFrom(newPage)) {
         break;
       }
-      // We found the page for all the consecutive pageless routes below. Those
-      // pageless routes do not need to be skipped.
-      pagelessRoutesToSkip = 0;
+
+      // We found the page for all the consecutive pageless routes below. Attach these
+      // pageless routes to the page.
+      if(unattachedPagelessRoutes.isNotEmpty) {
+         pageRouteToPagelessRoutes.putIfAbsent(
+          oldEntry,
+          () =>  List<_RouteEntry>.from(unattachedPagelessRoutes),
+        );
+        unattachedPagelessRoutes.clear();
+      }
+
       oldEntriesTop -= 1;
       newPagesTop -= 1;
     }
     // Reverts the pageless routes that cannot be updated.
-    oldEntriesTop += pagelessRoutesToSkip;
+    oldEntriesTop += unattachedPagelessRoutes.length;
 
     // Scans middle of the old entries and records the page key to old entry map.
     int oldEntriesBottomToScan = oldEntriesBottom;

packages/flutter/test/widgets/navigator_test.dart

@@ -3342,6 +3342,61 @@ void main() {
       expect(find.text('forth'), findsOneWidget);
     });
 
+    //Regression test for https://github.com/flutter/flutter/issues/115887
+    testWidgets('Complex case 2', (WidgetTester tester) async {
+      final GlobalKey<NavigatorState> navigator = GlobalKey<NavigatorState>();
+      List<TestPage> myPages = <TestPage>[
+        const TestPage(key: ValueKey<String>('1'), name:'initial'),
+        const TestPage(key: ValueKey<String>('2'), name:'second'),
+      ];
+
+      bool onPopPage(Route<dynamic> route, dynamic result) {
+        myPages.removeWhere((Page<dynamic> page) => route.settings == page);
+        return route.didPop(result);
+      }
+
+      await tester.pumpWidget(
+        buildNavigator(pages: myPages, onPopPage: onPopPage, key: navigator),
+      );
+      expect(find.text('second'), findsOneWidget);
+      expect(find.text('initial'), findsNothing);
+      // Push pageless route to second page route
+      navigator.currentState!.push(
+        MaterialPageRoute<void>(
+          builder: (BuildContext context) => const Text('second-pageless1'),
+        ),
+      );
+
+      await tester.pumpAndSettle();
+      // Now the history should look like [initial, second, second-pageless1].
+      expect(find.text('initial'), findsNothing);
+      expect(find.text('second'), findsNothing);
+      expect(find.text('second-pageless1'), findsOneWidget);
+      expect(myPages.length, 2);
+
+      myPages = <TestPage>[
+        const TestPage(key: ValueKey<String>('2'), name:'second'),
+      ];
+      await tester.pumpWidget(
+        buildNavigator(pages: myPages, onPopPage: onPopPage, key: navigator),
+      );
+      await tester.pumpAndSettle();
+
+      // Now the history should look like [second, second-pageless1].
+      expect(find.text('initial'), findsNothing);
+      expect(find.text('second'), findsNothing);
+      expect(find.text('second-pageless1'), findsOneWidget);
+      expect(myPages.length, 1);
+
+      // Pop the pageless route.
+      navigator.currentState!.pop();
+      await tester.pumpAndSettle();
+      expect(myPages.length, 1);
+      expect(find.text('initial'), findsNothing);
+      expect(find.text('second'), findsOneWidget);
+      expect(find.text('second-pageless1'), findsNothing);
+    });
+
     testWidgets('complex case 1 - with always remove transition delegate', (WidgetTester tester) async {
       final GlobalKey<NavigatorState> navigator = GlobalKey<NavigatorState>();
       final AlwaysRemoveTransitionDelegate transitionDelegate = AlwaysRemoveTransitionDelegate();