fix a tap gesture exception (#73846)

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

@@ -191,6 +191,14 @@ abstract class BaseTapGestureRecognizer extends PrimaryPointerGestureRecognizer
   void addAllowedPointer(PointerDownEvent event) {
     assert(event != null);
     if (state == GestureRecognizerState.ready) {
+      // If there is no result in the previous gesture arena,
+      // we ignore them and prepare to accept a new pointer.
+      if (_down != null && _up != null) {
+        assert(_down!.pointer == _up!.pointer);
+        _reset();
+      }
+
+      assert(_down == null && _up == null);
       // `_down` must be assigned in this method instead of `handlePrimaryPointer`,
       // because `acceptGesture` might be called before `handlePrimaryPointer`,
       // which relies on `_down` to call `handleTapDown`.
@@ -284,6 +292,7 @@ abstract class BaseTapGestureRecognizer extends PrimaryPointerGestureRecognizer
     if (!_wonArenaForPrimaryPointer || _up == null) {
       return;
     }
+    assert(_up!.pointer == _down!.pointer);
     handleTapUp(down: _down!, up: _up!);
     _reset();
   }

packages/flutter/test/gestures/double_tap_test.dart

@@ -622,4 +622,39 @@ void main() {
     recognized.clear();
     doubleTap.dispose();
   });
+
+  // Regression test for https://github.com/flutter/flutter/issues/73667
+  testGesture('Unfinished DoubleTap does not prevent competing Tap', (GestureTester tester) {
+    int tapCount = 0;
+    final DoubleTapGestureRecognizer doubleTap = DoubleTapGestureRecognizer()
+      ..onDoubleTap = () {};
+    final TapGestureRecognizer tap = TapGestureRecognizer()
+      ..onTap = () => tapCount++;
+
+    // Open a arena with 2 members and holding.
+    doubleTap.addPointer(down1);
+    tap.addPointer(down1);
+    tester.closeArena(1);
+    tester.route(down1);
+    tester.route(up1);
+    GestureBinding.instance!.gestureArena.sweep(1);
+
+    // Open a new arena with only one TapGestureRecognizer.
+    tester.async.elapse(const Duration(milliseconds: 100));
+    tap.addPointer(down2);
+    tester.closeArena(2);
+    tester.route(down2);
+    final PointerMoveEvent move2 = PointerMoveEvent(pointer: 2, position: down2.position);
+    tester.route(move2);
+    tester.route(up2);
+    expect(tapCount, 1); // The second tap will win immediately.
+    GestureBinding.instance!.gestureArena.sweep(2);
+
+    // Finish the previous gesture arena.
+    tester.async.elapse(const Duration(milliseconds: 300));
+    expect(tapCount, 1); // The first tap should not trigger onTap callback though it wins the arena.
+
+    tap.dispose();
+    doubleTap.dispose();
+  });
 }