Fix flip-flop behaviour with two competing taps (#10151)

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

@@ -58,6 +58,8 @@ abstract class GestureRecognizer extends GestureArenaMember {
 
   /// Invoke a callback provided by the application, catching and logging any
   /// exceptions.
+  ///
+  /// The `name` argument is ignored except when reporting exceptions.
   @protected
   T invokeCallback<T>(String name, RecognizerCallback<T> callback) {
     T result;
@@ -78,6 +80,9 @@ abstract class GestureRecognizer extends GestureArenaMember {
     }
     return result;
   }
+
+  @override
+  String toString() => '$runtimeType#$hashCode';
 }
 
 /// Base class for gesture recognizers that can only recognize one
@@ -109,7 +114,8 @@ abstract class OneSequenceGestureRecognizer extends GestureRecognizer {
   @protected
   void didStopTrackingLastPointer(int pointer);
 
-  /// Resolves this recognizer's participation in each gesture arena with the given disposition.
+  /// Resolves this recognizer's participation in each gesture arena with the
+  /// given disposition.
   @protected
   @mustCallSuper
   void resolve(GestureDisposition disposition) {
@@ -277,7 +283,7 @@ abstract class PrimaryPointerGestureRecognizer extends OneSequenceGestureRecogni
 
   @override
   void rejectGesture(int pointer) {
-    if (pointer == primaryPointer) {
+    if (pointer == primaryPointer && state == GestureRecognizerState.possible) {
       _stopTimer();
       state = GestureRecognizerState.defunct;
     }
@@ -285,6 +291,7 @@ abstract class PrimaryPointerGestureRecognizer extends OneSequenceGestureRecogni
 
   @override
   void didStopTrackingLastPointer(int pointer) {
+    assert(state != GestureRecognizerState.ready);
     _stopTimer();
     state = GestureRecognizerState.ready;
   }
@@ -307,4 +314,6 @@ abstract class PrimaryPointerGestureRecognizer extends OneSequenceGestureRecogni
     return offset.distance;
   }
 
+  @override
+  String toString() => '$runtimeType#$hashCode($state)';
 }

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

@@ -98,8 +98,10 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
   @override
   void resolve(GestureDisposition disposition) {
     if (_wonArenaForPrimaryPointer && disposition == GestureDisposition.rejected) {
+      // This can happen if the superclass decides the primary pointer
+      // exceeded the touch slop, or if the recognizer is disposed.
       if (onTapCancel != null)
-        invokeCallback<Null>('onTapCancel', onTapCancel); // ignore: STRONG_MODE_INVALID_CAST_FUNCTION_EXPR, https://github.com/dart-lang/sdk/issues/27504
+        invokeCallback<Null>('spontaneous onTapCancel', onTapCancel);
       _reset();
     }
     super.resolve(disposition);
@@ -124,9 +126,10 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
   void rejectGesture(int pointer) {
     super.rejectGesture(pointer);
     if (pointer == primaryPointer) {
-      assert(state == GestureRecognizerState.defunct);
+      // Another gesture won the arena.
+      assert(state != GestureRecognizerState.possible);
       if (onTapCancel != null)
-        invokeCallback<Null>('onTapCancel', onTapCancel); // ignore: STRONG_MODE_INVALID_CAST_FUNCTION_EXPR, https://github.com/dart-lang/sdk/issues/27504
+        invokeCallback<Null>('forced onTapCancel', onTapCancel);
       _reset();
     }
   }
@@ -134,7 +137,7 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
   void _checkDown() {
     if (!_sentTapDown) {
       if (onTapDown != null)
-        invokeCallback<Null>('onTapDown', () => onTapDown(new TapDownDetails(globalPosition: initialPosition))); // ignore: STRONG_MODE_INVALID_CAST_FUNCTION_EXPR, https://github.com/dart-lang/sdk/issues/27504
+        invokeCallback<Null>('onTapDown', () { onTapDown(new TapDownDetails(globalPosition: initialPosition)); });
       _sentTapDown = true;
     }
   }
@@ -143,9 +146,9 @@ class TapGestureRecognizer extends PrimaryPointerGestureRecognizer {
     if (_wonArenaForPrimaryPointer && _finalPosition != null) {
       resolve(GestureDisposition.accepted);
       if (onTapUp != null)
-        invokeCallback<Null>('onTapUp', () => onTapUp(new TapUpDetails(globalPosition: _finalPosition))); // ignore: STRONG_MODE_INVALID_CAST_FUNCTION_EXPR, https://github.com/dart-lang/sdk/issues/27504
+        invokeCallback<Null>('onTapUp', () { onTapUp(new TapUpDetails(globalPosition: _finalPosition)); });
       if (onTap != null)
-        invokeCallback<Null>('onTap', onTap); // ignore: STRONG_MODE_INVALID_CAST_FUNCTION_EXPR, https://github.com/dart-lang/sdk/issues/27504
+        invokeCallback<Null>('onTap', onTap);
       _reset();
     }
   }

packages/flutter/test/gestures/tap_test.dart

@@ -284,4 +284,75 @@ void main() {
     FlutterError.onError = previousErrorHandler;
     tap.dispose();
   });
+
+  testGesture('No duplicate tap events', (GestureTester tester) {
+    final TapGestureRecognizer tapA = new TapGestureRecognizer();
+    final TapGestureRecognizer tapB = new TapGestureRecognizer();
+
+    final List<String> log = <String>[];
+    tapA.onTapDown = (TapDownDetails details) { log.add('tapA onTapDown'); };
+    tapA.onTapUp = (TapUpDetails details) { log.add('tapA onTapUp'); };
+    tapA.onTap = () { log.add('tapA onTap'); };
+    tapA.onTapCancel = () { log.add('tapA onTapCancel'); };
+    tapB.onTapDown = (TapDownDetails details) { log.add('tapB onTapDown'); };
+    tapB.onTapUp = (TapUpDetails details) { log.add('tapB onTapUp'); };
+    tapB.onTap = () { log.add('tapB onTap'); };
+    tapB.onTapCancel = () { log.add('tapB onTapCancel'); };
+
+    log.add('start');
+    tapA.addPointer(down1);
+    log.add('added 1 to A');
+    tapB.addPointer(down1);
+    log.add('added 1 to B');
+    tester.closeArena(1);
+    log.add('closed 1');
+    tester.route(down1);
+    log.add('routed 1 down');
+    tester.route(up1);
+    log.add('routed 1 up');
+    GestureBinding.instance.gestureArena.sweep(1);
+    log.add('swept 1');
+    tapA.addPointer(down2);
+    log.add('down 2 to A');
+    tapB.addPointer(down2);
+    log.add('down 2 to B');
+    tester.closeArena(2);
+    log.add('closed 2');
+    tester.route(down2);
+    log.add('routed 2 down');
+    tester.route(up2);
+    log.add('routed 2 up');
+    GestureBinding.instance.gestureArena.sweep(2);
+    log.add('swept 2');
+    tapA.dispose();
+    log.add('disposed A');
+    tapB.dispose();
+    log.add('disposed B');
+
+    expect(log, <String>[
+      'start',
+      'added 1 to A',
+      'added 1 to B',
+      'closed 1',
+      'routed 1 down',
+      'routed 1 up',
+      'tapA onTapDown',
+      'tapA onTapUp',
+      'tapA onTap',
+      'tapB onTapCancel',
+      'swept 1',
+      'down 2 to A',
+      'down 2 to B',
+      'closed 2',
+      'routed 2 down',
+      'routed 2 up',
+      'tapA onTapDown',
+      'tapA onTapUp',
+      'tapA onTap',
+      'tapB onTapCancel',
+      'swept 2',
+      'disposed A',
+      'disposed B',
+    ]);
+  });
 }