Add semantic label finders (#29342)

* Add semantic label finders

packages/flutter_driver/lib/src/common/find.dart

@@ -135,6 +135,7 @@ abstract class SerializableFinder {
       case 'ByType': return ByType.deserialize(json);
       case 'ByValueKey': return ByValueKey.deserialize(json);
       case 'ByTooltipMessage': return ByTooltipMessage.deserialize(json);
+      case 'BySemanticsLabel': return BySemanticsLabel.deserialize(json);
       case 'ByText': return ByText.deserialize(json);
       case 'PageBack': return PageBack();
     }
@@ -164,6 +165,44 @@ class ByTooltipMessage extends SerializableFinder {
   }
 }
 
+/// A Flutter Driver finder that finds widgets by semantic label.
+///
+/// If the [label] property is a [String], the finder will try to find an exact
+/// match. If it is a [RegExp], it will return true for [RegExp.hasMatch].
+class BySemanticsLabel extends SerializableFinder {
+  /// Creates a semantic label finder given the [label].
+  BySemanticsLabel(this.label);
+
+  /// A [Pattern] matching the [Semantics.properties.label].
+  ///
+  /// If this is a [String], it will be treated as an exact match.
+  final Pattern label;
+
+  @override
+  final String finderType = 'BySemanticsLabel';
+
+  @override
+  Map<String, String> serialize() {
+    if (label is RegExp) {
+      final RegExp regExp = label;
+      return super.serialize()..addAll(<String, String>{
+        'label': regExp.pattern,
+        'isRegExp': 'true',
+      });
+    } else {
+      return super.serialize()..addAll(<String, String>{
+        'label': label,
+      });
+    }
+  }
+
+  /// Deserializes the finder from JSON generated by [serialize].
+  static BySemanticsLabel deserialize(Map<String, String> json) {
+    final bool isRegExp = json['isRegExp'] == 'true';
+    return BySemanticsLabel(isRegExp ? RegExp(json['label']) : json['label']);
+  }
+}
+
 /// A Flutter Driver finder that finds widgets by [text] inside a [Text] or
 /// [EditableText] widget.
 class ByText extends SerializableFinder {

packages/flutter_driver/lib/src/driver/driver.dart

@@ -939,6 +939,9 @@ class CommonFinders {
   /// Finds widgets with a tooltip with the given [message].
   SerializableFinder byTooltip(String message) => ByTooltipMessage(message);
 
+  /// Finds widgets with the given semantics [label].
+  SerializableFinder bySemanticsLabel(Pattern label) => BySemanticsLabel(label);
+
   /// Finds widgets whose class name matches the given string.
   SerializableFinder byType(String type) => ByType(type);
 

packages/flutter_driver/lib/src/extension/extension.dart

@@ -135,6 +135,7 @@ class FlutterDriverExtension {
     _finders.addAll(<String, FinderConstructor>{
       'ByText': (SerializableFinder finder) => _createByTextFinder(finder),
       'ByTooltipMessage': (SerializableFinder finder) => _createByTooltipMessageFinder(finder),
+      'BySemanticsLabel': (SerializableFinder finder) => _createBySemanticsLabelFinder(finder),
       'ByValueKey': (SerializableFinder finder) => _createByValueKeyFinder(finder),
       'ByType': (SerializableFinder finder) => _createByTypeFinder(finder),
       'PageBack': (SerializableFinder finder) => _createPageBackFinder(),
@@ -262,6 +263,22 @@ class FlutterDriverExtension {
     }, description: 'widget with text tooltip "${arguments.text}"');
   }
 
+  Finder _createBySemanticsLabelFinder(BySemanticsLabel arguments) {
+    return find.byElementPredicate((Element element) {
+      if (element is! RenderObjectElement) {
+        return false;
+      }
+      final String semanticsLabel = element.renderObject?.debugSemantics?.label;
+      if (semanticsLabel == null) {
+        return false;
+      }
+      final Pattern label = arguments.label;
+      return label is RegExp
+          ? label.hasMatch(semanticsLabel)
+          : label == semanticsLabel;
+    }, description: 'widget with semantic label "${arguments.label}"');
+  }
+
   Finder _createByValueKeyFinder(ByValueKey arguments) {
     switch (arguments.keyValueType) {
       case 'int':

packages/flutter_driver/test/flutter_driver_test.dart

@@ -158,6 +158,35 @@ void main() {
       });
     });
 
+    group('BySemanticsLabel', () {
+      test('finds by Semantic label using String', () async {
+        when(mockIsolate.invokeExtension(any, any)).thenAnswer((Invocation i) {
+          expect(i.positionalArguments[1], <String, String>{
+            'command': 'tap',
+            'timeout': _kSerializedTestTimeout,
+            'finderType': 'BySemanticsLabel',
+            'label': 'foo',
+          });
+          return makeMockResponse(<String, dynamic>{});
+        });
+        await driver.tap(find.bySemanticsLabel('foo'), timeout: _kTestTimeout);
+      });
+
+      test('finds by Semantic label using RegExp', () async {
+        when(mockIsolate.invokeExtension(any, any)).thenAnswer((Invocation i) {
+          expect(i.positionalArguments[1], <String, String>{
+            'command': 'tap',
+            'timeout': _kSerializedTestTimeout,
+            'finderType': 'BySemanticsLabel',
+            'label': '^foo',
+            'isRegExp': 'true',
+          });
+          return makeMockResponse(<String, dynamic>{});
+        });
+        await driver.tap(find.bySemanticsLabel(RegExp('^foo')), timeout: _kTestTimeout);
+      });
+    });
+
     group('tap', () {
       test('requires a target reference', () async {
         expect(driver.tap(null), throwsA(isInstanceOf<DriverError>()));

packages/flutter_test/lib/src/finders.dart

@@ -272,6 +272,51 @@ class CommonFinders {
   Finder ancestor({ Finder of, Finder matching, bool matchRoot = false }) {
     return _AncestorFinder(of, matching, matchRoot: matchRoot);
   }
+
+  /// Finds [Semantics] widgets matching the given `label`, either by
+  /// [RegExp.hasMatch] or string equality.
+  ///
+  /// The framework may combine semantics labels in certain scenarios, such as
+  /// when multiple [Text] widgets are in a [MaterialButton] widget. In such a
+  /// case, it may be preferable to match by regular expression. Consumers of
+  /// this API __must not__ introduce unsuitable content into the semantics tree
+  /// for the purposes of testing; in particular, you should prefer matching by
+  /// regular expression rather than by string if the framework has combined
+  /// your semantics, and not try to force the framework to break up the
+  /// semantics nodes. Breaking up the nodes would have an undesirable effect on
+  /// screen readers and other accessibility services.
+  ///
+  /// ## Sample code
+  ///
+  /// ```dart
+  /// expect(find.BySemanticsLabel('Back'), findsOneWidget);
+  /// ```
+  ///
+  /// If the `skipOffstage` argument is true (the default), then this skips
+  /// nodes that are [Offstage] or that are from inactive [Route]s.
+  Finder bySemanticsLabel(Pattern label, { bool skipOffstage = true }) {
+    if (WidgetsBinding.instance.pipelineOwner.semanticsOwner == null)
+      throw StateError('Semantics are not enabled. '
+                       'Make sure to call tester.enableSemantics() before using '
+                       'this finder, and call dispose on its return value after.');
+    return byElementPredicate(
+      (Element element) {
+        // Multiple elements can have the same renderObject - we want the "owner"
+        // of the renderObject, i.e. the RenderObjectElement.
+        if (element is! RenderObjectElement) {
+          return false;
+        }
+        final String semanticsLabel = element.renderObject?.debugSemantics?.label;
+        if (semanticsLabel == null) {
+          return false;
+        }
+        return label is RegExp
+            ? label.hasMatch(semanticsLabel)
+            : label == semanticsLabel;
+      },
+      skipOffstage: skipOffstage,
+    );
+  }
 }
 
 /// Searches a widget tree and returns nodes that match a particular

packages/flutter_test/test/finders_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/rendering.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -29,6 +30,53 @@ void main() {
     });
   });
 
+  group('semantics', () {
+    testWidgets('Throws StateError if semantics are not enabled', (WidgetTester tester) async {
+      expect(() => find.bySemanticsLabel('Add'), throwsStateError);
+    });
+
+    testWidgets('finds Semantically labeled widgets', (WidgetTester tester) async {
+      final SemanticsHandle semanticsHandle = tester.ensureSemantics();
+      await tester.pumpWidget(_boilerplate(
+        Semantics(
+          label: 'Add',
+          button: true,
+          child: const FlatButton(
+            child: Text('+'),
+            onPressed: null,
+          ),
+        ),
+      ));
+      expect(find.bySemanticsLabel('Add'), findsOneWidget);
+      semanticsHandle.dispose();
+    });
+
+    testWidgets('finds Semantically labeled widgets by RegExp', (WidgetTester tester) async {
+      final SemanticsHandle semanticsHandle = tester.ensureSemantics();
+      await tester.pumpWidget(_boilerplate(
+        Semantics(
+          container: true,
+          child: Row(children: const <Widget>[
+            Text('Hello'),
+            Text('World'),
+          ]),
+        ),
+      ));
+      expect(find.bySemanticsLabel('Hello'), findsNothing);
+      expect(find.bySemanticsLabel(RegExp(r'^Hello')), findsOneWidget);
+      semanticsHandle.dispose();
+    });
+
+    testWidgets('finds Semantically labeled widgets without explicit Semantics', (WidgetTester tester) async {
+      final SemanticsHandle semanticsHandle = tester.ensureSemantics();
+      await tester.pumpWidget(_boilerplate(
+        const SimpleCustomSemanticsWidget('Foo')
+      ));
+      expect(find.bySemanticsLabel('Foo'), findsOneWidget);
+      semanticsHandle.dispose();
+    });
+  });
+
   group('hitTestable', () {
     testWidgets('excludes non-hit-testable widgets', (WidgetTester tester) async {
       await tester.pumpWidget(
@@ -92,3 +140,28 @@ Widget _boilerplate(Widget child) {
     child: child,
   );
 }
+
+class SimpleCustomSemanticsWidget extends LeafRenderObjectWidget {
+  const SimpleCustomSemanticsWidget(this.label);
+
+  final String label;
+
+  @override
+  RenderObject createRenderObject(BuildContext context) => SimpleCustomSemanticsRenderObject(label);
+}
+
+class SimpleCustomSemanticsRenderObject extends RenderBox {
+  SimpleCustomSemanticsRenderObject(this.label);
+
+  final String label;
+
+  @override
+  bool get sizedByParent => true;
+
+  @override
+  void describeSemanticsConfiguration(SemanticsConfiguration config) {
+    super.describeSemanticsConfiguration(config);
+    config..label = label..textDirection = TextDirection.ltr;
+
+  }
+}
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