Navigator change backup (#38494)

* Broadcasting popRoute and pushRoute methods via SystemChannels.navigation. These messages will be used in flutter_web to detect the route

* Broadcasting popRoute and pushRoute methods via SystemChannels.navigation. These messages will be used in flutter_web to detect the route

* Reverting all unrelated formatting changes.

* Adding unit tests. Adding more comments.

* Changing string method names with constant strings.

* Fixing a constant strings.

* Fixing analyzer error.

* Fixing more white space.

* Changing the method names. Adding comments to the SystemChannels

* Comment and code name fixes

* replacing the comment with reviewer suggestion.

* addinf systemchannels.navigation mock to test bindings

* Adding a new class for sending route change notrifications. The nottifications are only sent on web. This should fix breaking android/ios

* using new class RouteNotificationMessages in navigator

* Fixing analyzer issues.

* fixing cycle dependency

* fixing github analyze error

* dartfmt two new classes. trying to fix anayze errors

* Update route_notification_messages.dart

* trying to fix white space errors

packages/flutter/lib/src/services/system_channels.dart

@@ -27,6 +27,24 @@ class SystemChannels {
   ///  * [WidgetsBindingObserver.didPopRoute] and
   ///    [WidgetsBindingObserver.didPushRoute], which expose this channel's
   ///    methods.
+  ///
+  /// The following methods are used for the opposite direction data flow. The
+  /// framework notifies the engine about the route changes.
+  ///
+  ///  * `routePushed`, which is called when a route is pushed. (e.g. A modal
+  ///  replaces the entire screen.)
+  ///
+  ///  * `routePopped`, which is called when a route is popped. (e.g. A dialog,
+  ///  such as time picker is closed.)
+  ///
+  ///  * `routeReplaced`, which is called when a route is replaced.
+  ///
+  /// See also:
+  ///
+  ///  * [Navigator] which manages transitions from one page to another.
+  ///    [Navigator.push], [Navigator.pushReplacement], [Navigator.pop] and
+  ///    [Navigator.replace], utilize this channel's methods to send route
+  ///    change information from framework to engine.
   static const MethodChannel navigation = MethodChannel(
       'flutter/navigation',
       JSONMethodCodec(),

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

@@ -9,6 +9,7 @@ import 'dart:developer' as developer;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
+import 'package:flutter/services.dart';
 
 import 'basic.dart';
 import 'binding.dart';
@@ -16,6 +17,7 @@ import 'focus_manager.dart';
 import 'focus_scope.dart';
 import 'framework.dart';
 import 'overlay.dart';
+import 'route_notification_messages.dart';
 import 'routes.dart';
 import 'ticker_provider.dart';
 
@@ -66,6 +68,18 @@ enum RoutePopDisposition {
   bubble,
 }
 
+/// Name for the method which is used for sending messages from framework to
+/// engine after a route is popped.
+const String _routePoppedMethod = 'routePopped';
+
+/// Name for the method which is used for sending messages from framework to
+/// engine after a route is pushed.
+const String _routePushedMethod = 'routePushed';
+
+/// Name for the method which is used for sending messages from framework to
+/// engine after a route is replaced.
+const String _routeReplacedMethod = 'routeReplaced';
+
 /// An abstraction for an entry managed by a [Navigator].
 ///
 /// This class defines an abstract interface between the navigator and the
@@ -1761,6 +1775,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
     }
     for (NavigatorObserver observer in widget.observers)
       observer.didPush(route, oldRoute);
+    RouteNotificationMessages.maybeNotifyRouteChange(_routePushedMethod, route, oldRoute);
     assert(() { _debugLocked = false; return true; }());
     _afterNavigation(route);
     return route.popped;
@@ -1854,6 +1869,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
     }
     for (NavigatorObserver observer in widget.observers)
       observer.didReplace(newRoute: newRoute, oldRoute: oldRoute);
+    RouteNotificationMessages.maybeNotifyRouteChange(_routeReplacedMethod, newRoute, oldRoute);
     assert(() { _debugLocked = false; return true; }());
     _afterNavigation(newRoute);
     return newRoute.popped;
@@ -1965,6 +1981,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
     }
     for (NavigatorObserver observer in widget.observers)
       observer.didReplace(newRoute: newRoute, oldRoute: oldRoute);
+    RouteNotificationMessages.maybeNotifyRouteChange(_routeReplacedMethod, newRoute, oldRoute);
     oldRoute.dispose();
     assert(() { _debugLocked = false; return true; }());
   }
@@ -2067,6 +2084,7 @@ class NavigatorState extends State<Navigator> with TickerProviderStateMixin {
         _history.last.didPopNext(route);
         for (NavigatorObserver observer in widget.observers)
           observer.didPop(route, _history.last);
+        RouteNotificationMessages.maybeNotifyRouteChange(_routePoppedMethod, route, _history.last);
       } else {
         assert(() { _debugLocked = false; return true; }());
         return false;

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

@@ -0,0 +1,42 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+
+import 'navigator.dart';
+
+/// Messages for route change notifications.
+class RouteNotificationMessages {
+  RouteNotificationMessages._();
+
+  /// When the engine is Web notify the platform for a route change.
+  static void maybeNotifyRouteChange(String methodName, Route<dynamic> route, Route<dynamic> previousRoute) {
+    if(kIsWeb) {
+      _notifyRouteChange(methodName, route, previousRoute);
+    } else {
+      // No op.
+    }
+  }
+
+  /// Notifies the platform of a route change.
+  ///
+  /// There are three methods: 'routePushed', 'routePopped', 'routeReplaced'.
+  ///
+  /// See also [SystemChannels.navigation], which handles subsequent navigation
+  /// requests.
+  static void _notifyRouteChange(String methodName, Route<dynamic> route, Route<dynamic> previousRoute) {
+    final String previousRouteName = previousRoute?.settings?.name;
+    final String routeName = route?.settings?.name;
+    if (previousRouteName != null || routeName != null) {
+      SystemChannels.navigation.invokeMethod<void>(
+        methodName,
+        <String, dynamic>{
+          'previousRouteName': previousRouteName,
+          'routeName': routeName,
+        },
+      );
+    }
+  }
+}

packages/flutter/test/widgets/route_notification_messages_test.dart

@@ -0,0 +1,174 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+@TestOn('chrome')
+
+import 'dart:ui';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+class OnTapPage extends StatelessWidget {
+  const OnTapPage({Key key, this.id, this.onTap}) : super(key: key);
+
+  final String id;
+  final VoidCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: Text('Page $id')),
+      body: GestureDetector(
+        onTap: onTap,
+        behavior: HitTestBehavior.opaque,
+        child: Container(
+          child: Center(
+            child: Text(id, style: Theme.of(context).textTheme.display2),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+void main() {
+  testWidgets('Push and Pop should send platform messages',
+      (WidgetTester tester) async {
+    final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
+      '/': (BuildContext context) => OnTapPage(
+          id: '/',
+          onTap: () {
+            Navigator.pushNamed(context, '/A');
+          }),
+      '/A': (BuildContext context) => OnTapPage(
+          id: 'A',
+          onTap: () {
+            Navigator.pop(context);
+          }),
+    };
+
+    final List<MethodCall> log = <MethodCall>[];
+
+    SystemChannels.navigation
+        .setMockMethodCallHandler((MethodCall methodCall) async {
+      log.add(methodCall);
+    });
+
+    await tester.pumpWidget(MaterialApp(
+      routes: routes,
+    ));
+
+    expect(log, hasLength(1));
+    expect(
+        log.last,
+        isMethodCall(
+          'routePushed',
+          arguments: <String, dynamic>{
+            'previousRouteName': null,
+            'routeName': '/'
+          },
+        ));
+
+    await tester.tap(find.text('/'));
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+
+    expect(log, hasLength(2));
+    expect(
+        log.last,
+        isMethodCall(
+          'routePushed',
+          arguments: <String, dynamic>{
+            'previousRouteName': '/',
+            'routeName': '/A'
+          },
+        ));
+
+    await tester.tap(find.text('A'));
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+
+    expect(log, hasLength(3));
+    expect(
+        log.last,
+        isMethodCall(
+          'routePopped',
+          arguments: <String, dynamic>{
+            'previousRouteName': '/',
+            'routeName': '/A'
+          },
+        ));
+  });
+
+  testWidgets('Replace should send platform messages',
+      (WidgetTester tester) async {
+    final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
+      '/': (BuildContext context) => OnTapPage(
+          id: '/',
+          onTap: () {
+            Navigator.pushNamed(context, '/A');
+          }),
+      '/A': (BuildContext context) => OnTapPage(
+          id: 'A',
+          onTap: () {
+            Navigator.pushReplacementNamed(context, '/B');
+          }),
+      '/B': (BuildContext context) => OnTapPage(id: 'B', onTap: () {}),
+    };
+
+    final List<MethodCall> log = <MethodCall>[];
+
+    SystemChannels.navigation
+        .setMockMethodCallHandler((MethodCall methodCall) async {
+      log.add(methodCall);
+    });
+
+    await tester.pumpWidget(MaterialApp(
+      routes: routes,
+    ));
+
+    expect(log, hasLength(1));
+    expect(
+        log.last,
+        isMethodCall(
+          'routePushed',
+          arguments: <String, dynamic>{
+            'previousRouteName': null,
+            'routeName': '/'
+          },
+        ));
+
+    await tester.tap(find.text('/'));
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+
+    expect(log, hasLength(2));
+    expect(
+        log.last,
+        isMethodCall(
+          'routePushed',
+          arguments: <String, dynamic>{
+            'previousRouteName': '/',
+            'routeName': '/A'
+          },
+        ));
+
+    await tester.tap(find.text('A'));
+    await tester.pump();
+    await tester.pump(const Duration(seconds: 1));
+
+    expect(log, hasLength(3));
+    expect(
+        log.last,
+        isMethodCall(
+          'routeReplaced',
+          arguments: <String, dynamic>{
+            'previousRouteName': '/A',
+            'routeName': '/B'
+          },
+        ));
+  });
+}

packages/flutter_test/lib/src/binding.dart

@@ -808,6 +808,10 @@ class AutomatedTestWidgetsFlutterBinding extends TestWidgetsFlutterBinding {
     final String assetFolderPath = Platform.environment['UNIT_TEST_ASSETS'];
     final String prefix =  'packages/${Platform.environment['APP_NAME']}/';
 
+    /// Navigation related actions (pop, push, replace) broadcasts these actions via
+    /// platform messages.
+    SystemChannels.navigation.setMockMethodCallHandler((MethodCall methodCall) async {});
+
     defaultBinaryMessenger.setMockMessageHandler('flutter/assets', (ByteData message) {
       String key = utf8.decode(message.buffer.asUint8List());
       File asset = File(path.join(assetFolderPath, key));