Check for initialRoute before Navigator.defaultRouteName (#10216)

* Check for initialRoute before Navigator.defaultRouteName

* Default initialRoute to Navigator.defaultRouteName

* Take suggestions from code review

* Add test for old and new routes behavior

* Revert "Add test for old and new routes behavior"

This reverts commit 282fb64b165ed532583e9a5d2e4debe29469fba4.

* Retry: without dartfmt, with dartanalyzer

* Rename tests, check the routes are taken

* Fix flutter analyze --flutter-repo warnings

* Add test for initial vs default route

* Update test and fix analyzer warnings

* Add test for initial route only being used initially

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

@@ -42,8 +42,9 @@ class MaterialApp extends StatefulWidget {
   /// Creates a MaterialApp.
   ///
   /// At least one of [home], [routes], or [onGenerateRoute] must be
-  /// given. If only [routes] is given, it must include an entry for
-  /// the [Navigator.defaultRouteName] (`'/'`).
+  /// given. If only [routes] is given, it must include an entry for the
+  /// [initialRoute], which defaults to [Navigator.defaultRouteName]
+  /// (`'/'`).
   ///
   /// This class creates an instance of [WidgetsApp].
   MaterialApp({
@@ -53,7 +54,7 @@ class MaterialApp extends StatefulWidget {
     this.theme,
     this.home,
     this.routes: const <String, WidgetBuilder>{},
-    this.initialRoute,
+    this.initialRoute: Navigator.defaultRouteName,
     this.onGenerateRoute,
     this.onLocaleChanged,
     this.navigatorObservers: const <NavigatorObserver>[],
@@ -65,8 +66,8 @@ class MaterialApp extends StatefulWidget {
     this.debugShowCheckedModeBanner: true
   }) : assert(debugShowMaterialGrid != null),
        assert(routes != null),
-       assert(!routes.containsKey(Navigator.defaultRouteName) || (home == null)),
-       assert(routes.containsKey(Navigator.defaultRouteName) || (home != null) || (onGenerateRoute != null)),
+       assert(!routes.containsKey(initialRoute) || (home == null)),
+       assert(routes.containsKey(initialRoute) || (home != null) || (onGenerateRoute != null)),
        super(key: key);
 
   /// A one-line description of this app for use in the window manager.

packages/flutter/test/material/app_test.dart

@@ -143,4 +143,76 @@ void main() {
 
     expect(find.text('Home'), findsOneWidget);
   });
+
+  testWidgets('Default initialRoute', (WidgetTester tester) async {
+    await tester.pumpWidget(new MaterialApp(routes: <String, WidgetBuilder>{
+      '/': (BuildContext context) => const Text('route "/"'),
+    }));
+
+    expect(find.text('route "/"'), findsOneWidget);
+  });
+
+  testWidgets('Custom initialRoute only', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      new MaterialApp(
+        initialRoute: '/a',
+        routes: <String, WidgetBuilder>{
+          '/a': (BuildContext context) => const Text('route "/a"'),
+        },
+      )
+    );
+
+    expect(find.text('route "/a"'), findsOneWidget);
+  });
+
+  testWidgets('Custom initialRoute along with Navigator.defaultRouteName', (WidgetTester tester) async {
+    final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
+      '/': (BuildContext context) => const Text('route "/"'),
+      '/a': (BuildContext context) => const Text('route "/a"'),
+      '/b': (BuildContext context) => const Text('route "/b"'),
+    };
+
+    await tester.pumpWidget(
+      new MaterialApp(
+        initialRoute: '/a',
+        routes: routes,
+      )
+    );
+    expect(find.text('route "/"'), findsNothing);
+    expect(find.text('route "/a"'), findsOneWidget);
+    expect(find.text('route "/b"'), findsNothing);
+  });
+
+  testWidgets('Make sure initialRoute is only used the first time', (WidgetTester tester) async {
+    final Map<String, WidgetBuilder> routes = <String, WidgetBuilder>{
+      '/': (BuildContext context) => const Text('route "/"'),
+      '/a': (BuildContext context) => const Text('route "/a"'),
+      '/b': (BuildContext context) => const Text('route "/b"'),
+    };
+
+    await tester.pumpWidget(
+      new MaterialApp(
+        initialRoute: '/a',
+        routes: routes,
+      )
+    );
+    expect(find.text('route "/"'), findsNothing);
+    expect(find.text('route "/a"'), findsOneWidget);
+    expect(find.text('route "/b"'), findsNothing);
+
+    await tester.pumpWidget(
+      new MaterialApp(
+        initialRoute: '/b',
+        routes: routes,
+      )
+    );
+    expect(find.text('route "/"'), findsNothing);
+    expect(find.text('route "/a"'), findsOneWidget);
+    expect(find.text('route "/b"'), findsNothing);
+
+    await tester.pumpWidget(new MaterialApp(routes: routes));
+    expect(find.text('route "/"'), findsNothing);
+    expect(find.text('route "/a"'), findsOneWidget);
+    expect(find.text('route "/b"'), findsNothing);
+  });
 }