only tap on widgets reachable by hit testing (#11767)

* only tap on widgets reachable by hit testing

* use FractionalOffset

* added tests

* check finder finds correct widget

* undo unintentional changes

* address comments

* style fix

* add Directionality in test

* fix analysis warning

dev/devicelab/lib/tasks/integration_ui.dart

@@ -21,7 +21,14 @@ Future<TaskResult> runEndToEndTests() async {
     if (deviceOperatingSystem == DeviceOperatingSystem.ios)
       await prepareProvisioningCertificates(testDirectory.path);
 
-    await flutter('drive', options: <String>['--verbose', '-d', deviceId, 'lib/keyboard_resize.dart']);
+    const List<String> entryPoints = const <String>[
+      'lib/keyboard_resize.dart',
+      'lib/driver.dart',
+    ];
+
+    for (final String entryPoint in entryPoints) {
+      await flutter('drive', options: <String>['--verbose', '-d', deviceId, entryPoint]);
+    }
   });
 
   return new TaskResult.success(<String, dynamic>{});

dev/integration_tests/ui/lib/driver.dart

@@ -23,6 +23,7 @@ class DriverTestApp extends StatefulWidget {
 
 class DriverTestAppState extends State<DriverTestApp> {
   bool present = true;
+  Letter _selectedValue = Letter.a;
 
   @override
   Widget build(BuildContext context) {
@@ -52,9 +53,41 @@ class DriverTestAppState extends State<DriverTestApp> {
                 ),
               ],
             ),
+            new Row(
+              children: <Widget>[
+                const Expanded(
+                  child: const Text('hit testability'),
+                ),
+                new DropdownButton<Letter>(
+                  key: const ValueKey<String>('dropdown'),
+                  value: _selectedValue,
+                  onChanged: (Letter newValue) {
+                    setState(() {
+                      _selectedValue = newValue;
+                    });
+                  },
+                  items: <DropdownMenuItem<Letter>>[
+                    const DropdownMenuItem<Letter>(
+                      value: Letter.a,
+                      child: const Text('Aaa', key: const ValueKey<String>('a')),
+                    ),
+                    const DropdownMenuItem<Letter>(
+                      value: Letter.b,
+                      child: const Text('Bbb', key: const ValueKey<String>('b')),
+                    ),
+                    const DropdownMenuItem<Letter>(
+                      value: Letter.c,
+                      child: const Text('Ccc', key: const ValueKey<String>('c')),
+                    ),
+                  ],
+                ),
+              ],
+            ),
           ],
         ),
       ),
     );
   }
 }
+
+enum Letter { a, b, c }

dev/integration_tests/ui/test_driver/driver_test.dart

@@ -77,5 +77,21 @@ void main() {
     test('waitForAbsent resolves immediately when the element does not exist', () async {
       await driver.waitForAbsent(find.text('that does not exist'));
     });
+
+    test('uses hit test to determine tappable elements', () async {
+      final SerializableFinder a = find.byValueKey('a');
+      final SerializableFinder menu = find.byType('_DropdownMenu<Letter>');
+
+      // Dropdown is closed
+      await driver.waitForAbsent(menu);
+
+      // Open dropdown
+      await driver.tap(a);
+      await driver.waitFor(menu);
+
+      // Close it again
+      await driver.tap(a);
+      await driver.waitForAbsent(menu);
+    });
   });
 }

packages/flutter_driver/lib/src/extension.dart

@@ -262,7 +262,10 @@ class FlutterDriverExtension {
 
   Future<TapResult> _tap(Command command) async {
     final Tap tapCommand = command;
-    await _prober.tap(await _waitForElement(_createFinder(tapCommand.finder)));
+    final Finder computedFinder = await _waitForElement(
+      _createFinder(tapCommand.finder).hitTestable()
+    );
+    await _prober.tap(computedFinder);
     return new TapResult();
   }
 

packages/flutter_test/lib/src/finders.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/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:meta/meta.dart';
 
@@ -284,6 +285,13 @@ abstract class Finder {
   /// matched by this finder.
   Finder get last => new _LastFinder(this);
 
+  /// Returns a variant of this finder that only matches elements reachable by
+  /// a hit test.
+  ///
+  /// The [at] parameter specifies the location relative to the size of the
+  /// target element where the hit test is performed.
+  Finder hitTestable({ FractionalOffset at: FractionalOffset.center }) => new _HitTestableFinder(this, at);
+
   @override
   String toString() {
     final String additional = skipOffstage ? ' (ignoring offstage widgets)' : '';
@@ -327,6 +335,33 @@ class _LastFinder extends Finder {
   }
 }
 
+class _HitTestableFinder extends Finder {
+  _HitTestableFinder(this.parent, this.offset);
+
+  final Finder parent;
+  final FractionalOffset offset;
+
+  @override
+  String get description => '${parent.description} (considering only hit-testable ones)';
+
+  @override
+  Iterable<Element> apply(Iterable<Element> candidates) sync* {
+    for (final Element candidate in parent.apply(candidates)) {
+      final RenderBox box = candidate.renderObject;
+      assert(box != null);
+      final Offset absoluteOffset = box.localToGlobal(offset.alongSize(box.size));
+      final HitTestResult hitResult = new HitTestResult();
+      WidgetsBinding.instance.hitTest(hitResult, absoluteOffset);
+      for (final HitTestEntry entry in hitResult.path) {
+        if (entry.target == candidate.renderObject) {
+          yield candidate;
+          break;
+        }
+      }
+    }
+  }
+}
+
 /// Searches a widget tree and returns nodes that match a particular
 /// pattern.
 abstract class MatchFinder extends Finder {

packages/flutter_test/test/finders_test.dart

@@ -0,0 +1,44 @@
+// Copyright 2016 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/material.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('hitTestable', () {
+    testWidgets('excludes non-hit-testable widgets', (WidgetTester tester) async {
+      await tester.pumpWidget(
+        _boilerplate(new IndexedStack(
+          sizing: StackFit.expand,
+          children: <Widget>[
+            new GestureDetector(
+              key: const ValueKey<int>(0),
+              behavior: HitTestBehavior.opaque,
+              onTap: () { },
+              child: const SizedBox.expand(),
+            ),
+            new GestureDetector(
+              key: const ValueKey<int>(1),
+              behavior: HitTestBehavior.opaque,
+              onTap: () { },
+              child: const SizedBox.expand(),
+            ),
+          ],
+        )),
+      );
+      expect(find.byType(GestureDetector), findsNWidgets(2));
+      final Finder hitTestable = find.byType(GestureDetector).hitTestable(at: const FractionalOffset(0.5, 0.5));
+      expect(hitTestable, findsOneWidget);
+      expect(tester.widget(hitTestable).key, const ValueKey<int>(0));
+    });
+  });
+}
+
+Widget _boilerplate(Widget child) {
+  return new Directionality(
+    textDirection: TextDirection.ltr,
+    child: child,
+  );
+}