Short circuit _checkUp if tap callbacks were triggered by resolve. (#12521)

packages/flutter/lib/src/gestures/tap.dart

@@ -2,6 +2,8 @@
 // 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 'arena.dart';
 import 'constants.dart';
 import 'events.dart';
@@ -90,6 +92,8 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
     if (event is PointerUpEvent) {
       _finalPosition = event.position;
       _checkUp();
+    } else if (event is PointerCancelEvent) {
+      _reset();
     }
   }
 
@@ -143,6 +147,14 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
   void _checkUp() {
     if (_wonArenaForPrimaryPointer && _finalPosition != null) {
       resolve(GestureDisposition.accepted);
+      if (!_wonArenaForPrimaryPointer || _finalPosition == null) {
+        // It is possible that resolve has just recursively called _checkUp
+        // (see https://github.com/flutter/flutter/issues/12470).
+        // In that case _wonArenaForPrimaryPointer will be false (as _checkUp
+        // calls _reset) and we return here to avoid double invocation of the
+        // tap callbacks.
+        return;
+      }
       if (onTapUp != null)
         invokeCallback<Null>('onTapUp', () { onTapUp(new TapUpDetails(globalPosition: _finalPosition)); });
       if (onTap != null)
@@ -159,4 +171,12 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
 
   @override
   String get debugDescription => 'tap';
+
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder description) {
+    super.debugFillProperties(description);
+    description.add(new FlagProperty('wonArenaForPrimaryPointer', value: _wonArenaForPrimaryPointer, ifTrue: 'won arena'));
+    description.add(new DiagnosticsProperty<Offset>('finalPosition', _finalPosition, defaultValue: null));
+    description.add(new FlagProperty('sentTapDown', value: _sentTapDown, ifTrue: 'sent tap down'));
+  }
 }

packages/flutter/test/gestures/debug_test.dart

@@ -43,7 +43,7 @@ void main() {
     GestureBinding.instance.gestureArena.sweep(1);
     expect(log, hasLength(2));
     expect(log[0], equalsIgnoringHashCodes('Gesture arena 1    ❙ Sweeping with 1 member.'));
-    expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Winner: TapGestureRecognizer#00000(state: ready)'));
+    expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Winner: TapGestureRecognizer#00000(state: ready, finalPosition: Offset(12.0, 8.0))'));
     log.clear();
 
     tap.dispose();
@@ -83,9 +83,9 @@ void main() {
 
     GestureBinding.instance.gestureArena.sweep(1);
     expect(log, hasLength(3));
-    expect(log[0], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready) calling onTapDown callback.'));
-    expect(log[1], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready) calling onTapUp callback.'));
-    expect(log[2], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready) calling onTap callback.'));
+    expect(log[0], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready, finalPosition: Offset(12.0, 8.0)) calling onTapDown callback.'));
+    expect(log[1], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready, won arena, finalPosition: Offset(12.0, 8.0), sent tap down) calling onTapUp callback.'));
+    expect(log[2], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready, won arena, finalPosition: Offset(12.0, 8.0), sent tap down) calling onTap callback.'));
     log.clear();
 
     tap.dispose();
@@ -132,10 +132,10 @@ void main() {
     GestureBinding.instance.gestureArena.sweep(1);
     expect(log, hasLength(5));
     expect(log[0], equalsIgnoringHashCodes('Gesture arena 1    ❙ Sweeping with 1 member.'));
-    expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Winner: TapGestureRecognizer#00000(state: ready)'));
-    expect(log[2], equalsIgnoringHashCodes('                   ❙ TapGestureRecognizer#00000(state: ready) calling onTapDown callback.'));
-    expect(log[3], equalsIgnoringHashCodes('                   ❙ TapGestureRecognizer#00000(state: ready) calling onTapUp callback.'));
-    expect(log[4], equalsIgnoringHashCodes('                   ❙ TapGestureRecognizer#00000(state: ready) calling onTap callback.'));
+    expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Winner: TapGestureRecognizer#00000(state: ready, finalPosition: Offset(12.0, 8.0))'));
+    expect(log[2], equalsIgnoringHashCodes('                   ❙ TapGestureRecognizer#00000(state: ready, finalPosition: Offset(12.0, 8.0)) calling onTapDown callback.'));
+    expect(log[3], equalsIgnoringHashCodes('                   ❙ TapGestureRecognizer#00000(state: ready, won arena, finalPosition: Offset(12.0, 8.0), sent tap down) calling onTapUp callback.'));
+    expect(log[4], equalsIgnoringHashCodes('                   ❙ TapGestureRecognizer#00000(state: ready, won arena, finalPosition: Offset(12.0, 8.0), sent tap down) calling onTap callback.'));
     log.clear();
 
     tap.dispose();
@@ -145,4 +145,13 @@ void main() {
     debugPrintRecognizerCallbacksTrace = false;
     debugPrint = oldCallback;
   });
+
+  test('TapGestureRecognizer _sentTapDown toString', () {
+    final TapGestureRecognizer tap = new TapGestureRecognizer();
+    expect(tap.toString(), equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready)'));
+    final PointerEvent event = const PointerDownEvent(pointer: 1, position: const Offset(10.0, 10.0));
+    tap.addPointer(event);
+    tap.didExceedDeadline();
+    expect(tap.toString(), equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: possible, sent tap down)'));
+  });
 }

packages/flutter/test/widgets/gesture_disambiguation_test.dart

+// Copyright 2017 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_test/flutter_test.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter/gestures.dart';
+
+void main() {
+  testWidgets('onTap detection with canceled pointer and a drag listener', (WidgetTester tester) async {
+    int detector1TapCount = 0;
+    int detector2TapCount = 0;
+
+    final Widget widget = new GestureDetector(
+      child: new Column(
+        mainAxisAlignment: MainAxisAlignment.start,
+        children: <Widget>[
+          new GestureDetector(
+            onTap: () { detector1TapCount += 1; },
+            behavior: HitTestBehavior.opaque,
+            child: const SizedBox(width: 200.0, height: 200.0),
+          ),
+          new GestureDetector(
+            onTap: () { detector2TapCount += 1; },
+            behavior: HitTestBehavior.opaque,
+            child: const SizedBox(width: 200.0, height: 200.0)
+          )
+        ],
+      )
+    );
+
+    await tester.pumpWidget(widget);
+
+    // The following pointer event sequence was causing the issue described
+    // in https://github.com/flutter/flutter/issues/12470 by triggering 2 tap
+    // events on the second detector.
+    final TestGesture gesture1 = await tester.startGesture(const Offset(400.0, 10.0));
+    final TestGesture gesture2 = await tester.startGesture(const Offset(400.0, 210.0));
+    await gesture1.up();
+    await gesture2.cancel();
+    final TestGesture gesture3 = await tester.startGesture(const Offset(400.0, 250.0));
+    await gesture3.up();
+
+    expect(detector1TapCount, 1);
+    expect(detector2TapCount, 1);
+  });
+}