Reland: Add optional param to useRootNavigator when showSearch (#84872)

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

@@ -35,6 +35,12 @@ import 'theme.dart';
 /// call. Call [SearchDelegate.close] before re-using the same delegate instance
 /// for another [showSearch] call.
 ///
+/// The `useRootNavigator` argument is used to determine whether to push the
+/// search page to the [Navigator] furthest from or nearest to the given
+/// `context`. By default, `useRootNavigator` is `false` and the search page
+/// route created by this method is pushed to the nearest navigator to the
+/// given `context`. It can not be `null`.
+///
 /// The transition to the search page triggered by this method looks best if the
 /// screen triggering the transition contains an [AppBar] at the top and the
 /// transition is called from an [IconButton] that's part of [AppBar.actions].
@@ -54,12 +60,14 @@ Future<T?> showSearch<T>({
   required BuildContext context,
   required SearchDelegate<T> delegate,
   String? query = '',
+  bool useRootNavigator = false,
 }) {
   assert(delegate != null);
   assert(context != null);
+  assert(useRootNavigator != null);
   delegate.query = query ?? delegate.query;
   delegate._currentBody = _SearchBody.suggestions;
-  return Navigator.of(context).push(_SearchPageRoute<T>(
+  return Navigator.of(context, rootNavigator: useRootNavigator).push(_SearchPageRoute<T>(
     delegate: delegate,
   ));
 }

packages/flutter/test/material/search_test.dart

@@ -841,6 +841,66 @@ void main() {
     expect(find.text('Suggestions'), findsNothing);
     expect(selectedResults, <String>['Result']);
   });
+
+  testWidgets('showSearch with useRootNavigator', (WidgetTester tester) async {
+    final _MyNavigatorObserver rootObserver = _MyNavigatorObserver();
+    final _MyNavigatorObserver localObserver = _MyNavigatorObserver();
+
+    final _TestEmptySearchDelegate delegate = _TestEmptySearchDelegate(
+      result: 'Result',
+      suggestions: 'Suggestions',
+    );
+
+    await tester.pumpWidget(MaterialApp(
+      navigatorObservers: <NavigatorObserver>[rootObserver],
+      home: Navigator(
+        observers: <NavigatorObserver>[localObserver],
+        onGenerateRoute: (RouteSettings settings) {
+          if (settings.name == 'nested') {
+            return MaterialPageRoute<dynamic>(
+              builder: (BuildContext context) => Column(
+                mainAxisAlignment: MainAxisAlignment.center,
+                children: <Widget>[
+                  TextButton(
+                      onPressed: () async {
+                        await showSearch(context: context, delegate: delegate, useRootNavigator: true);
+                      },
+                      child: const Text('showSearchRootNavigator')),
+                  TextButton(
+                      onPressed: () async {
+                        await showSearch(context: context, delegate: delegate);
+                      },
+                      child: const Text('showSearchLocalNavigator')),
+                ],
+              ),
+              settings: settings,
+            );
+          }
+          throw UnimplementedError();
+        },
+        initialRoute: 'nested',
+      ),
+    ));
+
+    expect(rootObserver.pushCount, 0);
+    expect(localObserver.pushCount, 0);
+
+    // showSearch normal and back
+    await tester.tap(find.text('showSearchLocalNavigator'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.byTooltip('Close'));
+    await tester.pumpAndSettle();
+    expect(rootObserver.pushCount, 0);
+    expect(localObserver.pushCount, 1);
+
+    // showSearch with rootNavigator
+    await tester.tap(find.text('showSearchRootNavigator'));
+    await tester.pumpAndSettle();
+    await tester.tap(find.byTooltip('Close'));
+    await tester.pumpAndSettle();
+    expect(rootObserver.pushCount, 1);
+    expect(localObserver.pushCount, 1);
+  });
 }
 
 class TestHomePage extends StatelessWidget {
@@ -1026,3 +1086,16 @@ class _TestEmptySearchDelegate extends SearchDelegate<String> {
     );
   }
 }
+
+class _MyNavigatorObserver extends NavigatorObserver {
+  int pushCount = 0;
+
+  @override
+  void didPush(Route<dynamic> route, Route<dynamic>? previousRoute) {
+    // don't count the root route
+    if (<String>['nested', '/'].contains(route.settings.name)) {
+      return;
+    }
+    pushCount++;
+  }
+}