fix(android): Clear stale drag state when a nested horizontal ScrollView takes a touch

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.kt

@@ -644,6 +644,14 @@ constructor(context: Context, private val fpsListener: FpsListener? = null) :
         ev.action == MotionEvent.ACTION_DOWN &&
             findDeepestScrollViewForMotionEvent(this, ev) != null
     ) {
+      // Skipping super keeps a stale pointer from a gesture a child claimed; clear it.
+      // A cancel also stops the scroller, so leave a running fling or snap alone.
+      if (scroller?.isFinished != false) {
+        val cancel = MotionEvent.obtain(ev)
+        cancel.action = MotionEvent.ACTION_CANCEL
+        super.onInterceptTouchEvent(cancel)
+        cancel.recycle()
+      }
       return false
     }
 

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/scroll/ReactHorizontalScrollViewNestedInterceptTest.kt

@@ -0,0 +1,144 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.views.scroll
+
+import android.util.DisplayMetrics
+import android.view.MotionEvent
+import android.view.View
+import android.widget.FrameLayout
+import android.widget.HorizontalScrollView
+import android.widget.OverScroller
+import androidx.core.view.ViewCompat
+import com.facebook.react.bridge.BridgeReactContext
+import com.facebook.react.bridge.ReactTestHelper.createMockCatalystInstance
+import com.facebook.react.internal.featureflags.ReactNativeFeatureFlagsForTests
+import com.facebook.react.uimanager.DisplayMetricsHolder
+import com.facebook.react.uimanager.ThemedReactContext
+import com.facebook.react.uimanager.UIManagerHelper
+import com.facebook.react.uimanager.events.EventDispatcher
+import com.facebook.soloader.SoLoader
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.MockedStatic
+import org.mockito.Mockito.mockStatic
+import org.mockito.kotlin.any
+import org.mockito.kotlin.mock
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.RuntimeEnvironment
+
+/** Verifies that a drag starting on a nested horizontal ScrollView is left to that child. */
+@RunWith(RobolectricTestRunner::class)
+class ReactHorizontalScrollViewNestedInterceptTest {
+
+  private lateinit var themedContext: ThemedReactContext
+  private lateinit var uiManagerHelperMock: MockedStatic<UIManagerHelper>
+
+  @Before
+  fun setup() {
+    ReactNativeFeatureFlagsForTests.setUp()
+    SoLoader.setInTestMode()
+    val context = BridgeReactContext(RuntimeEnvironment.getApplication())
+    context.initializeWithInstance(createMockCatalystInstance())
+    themedContext = ThemedReactContext(context, context, null, -1)
+    DisplayMetricsHolder.setScreenDisplayMetrics(DisplayMetrics())
+    uiManagerHelperMock = mockStatic(UIManagerHelper::class.java)
+    uiManagerHelperMock
+        .`when`<EventDispatcher?> { UIManagerHelper.getEventDispatcher(any()) }
+        .thenReturn(mock())
+  }
+
+  @After
+  fun teardown() {
+    uiManagerHelperMock.close()
+    DisplayMetricsHolder.setScreenDisplayMetrics(null)
+  }
+
+  @Test
+  fun testDragOnNestedScrollViewIsNotIntercepted() {
+    val outer = createOuterWithNestedScrollView()
+
+    assertThat(outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_DOWN, 800f, NESTED_Y)))
+        .isFalse()
+    assertThat(outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_MOVE, 400f, NESTED_Y)))
+        .isFalse()
+  }
+
+  @Test
+  fun testDragOnNestedScrollViewIsNotInterceptedAfterAnUnfinishedGesture() {
+    val outer = createOuterWithNestedScrollView()
+    // Starts outside the nested view, then a child claims it: no UP or CANCEL arrives.
+    assertThat(outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_DOWN, 200f, OUTSIDE_Y)))
+        .isFalse()
+
+    assertThat(outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_DOWN, 800f, NESTED_Y)))
+        .isFalse()
+    assertThat(outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_MOVE, 780f, NESTED_Y)))
+        .isFalse()
+  }
+
+  @Test
+  fun testDragOutsideNestedScrollViewIsStillIntercepted() {
+    val outer = createOuterWithNestedScrollView()
+
+    assertThat(outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_DOWN, 800f, OUTSIDE_Y)))
+        .isFalse()
+    assertThat(outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_MOVE, 400f, OUTSIDE_Y)))
+        .isTrue()
+  }
+
+  @Test
+  fun testTouchOnNestedScrollViewDoesNotStopAFling() {
+    val outer = createOuterWithNestedScrollView()
+    outer.fling(FLING_VELOCITY)
+    val scroller = outerScroller(outer)
+    assertThat(scroller.isFinished).isFalse()
+
+    outer.onInterceptTouchEvent(obtain(MotionEvent.ACTION_DOWN, 800f, NESTED_Y))
+
+    assertThat(scroller.isFinished).isFalse()
+  }
+
+  private fun outerScroller(view: ReactHorizontalScrollView): OverScroller {
+    val field = HorizontalScrollView::class.java.getDeclaredField("mScroller")
+    field.isAccessible = true
+    return field.get(view) as OverScroller
+  }
+
+  private fun createOuterWithNestedScrollView(): ReactHorizontalScrollView {
+    val outer = ReactHorizontalScrollView(themedContext)
+    val content = FrameLayout(themedContext)
+    val nested = ReactHorizontalScrollView(themedContext)
+    ViewCompat.setNestedScrollingEnabled(nested, true)
+    val nestedContent = View(themedContext)
+    nested.addView(nestedContent)
+    content.addView(nested)
+    outer.addView(content)
+
+    // Top-down: a parent's layout pass resets unmeasured children.
+    outer.layout(0, 0, VIEWPORT_SIZE, VIEWPORT_SIZE)
+    content.layout(0, 0, VIEWPORT_SIZE * 2, VIEWPORT_SIZE)
+    nested.layout(0, NESTED_TOP, VIEWPORT_SIZE, NESTED_TOP + NESTED_HEIGHT)
+    nestedContent.layout(0, 0, VIEWPORT_SIZE * 3, NESTED_HEIGHT)
+    return outer
+  }
+
+  private fun obtain(action: Int, x: Float, y: Float): MotionEvent =
+      MotionEvent.obtain(0L, 0L, action, x, y, 0)
+
+  private companion object {
+    const val VIEWPORT_SIZE = 1000
+    const val NESTED_TOP = 500
+    const val NESTED_HEIGHT = 200
+    const val NESTED_Y = 600f
+    const val OUTSIDE_Y = 200f
+    const val FLING_VELOCITY = 5000
+  }
+}