Fix regression in SwipeToScene

This CL fixes a regression caused by ag/25992835: now that
MultiPointerDraggableNode.enabled is a lambda (that might never change),
we need to explicitly observe the result of this lambda to reset the
associated pointer input whenever enabled is changed.

Bug: 291071158
Test: atest SwipeToSceneTest
Flag: N/A
Change-Id: I476228f9f5e66d1b69de33b0879f62507ce31980

2 files changed, 80 insertions, 14 deletions

diff --git a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/MultiPointerDraggable.kt b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/MultiPointerDraggable.kt
index 436e5bf6debd..7c4fd5a32596 100644
--- a/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/MultiPointerDraggable.kt
+++ b/packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/MultiPointerDraggable.kt
@@ -40,8 +40,10 @@ import androidx.compose.ui.input.pointer.util.addPointerInputChange
 import androidx.compose.ui.node.CompositionLocalConsumerModifierNode
 import androidx.compose.ui.node.DelegatingNode
 import androidx.compose.ui.node.ModifierNodeElement
+import androidx.compose.ui.node.ObserverModifierNode
 import androidx.compose.ui.node.PointerInputModifierNode
 import androidx.compose.ui.node.currentValueOf
+import androidx.compose.ui.node.observeReads
 import androidx.compose.ui.platform.LocalViewConfiguration
 import androidx.compose.ui.unit.IntSize
 import androidx.compose.ui.unit.Velocity
@@ -118,10 +120,15 @@ internal class MultiPointerDraggableNode(
     var onDragStarted: (startedPosition: Offset, overSlop: Float, pointersDown: Int) -> Unit,
     var onDragDelta: (Float) -> Unit,
     var onDragStopped: (velocity: Float) -> Unit,
-) : PointerInputModifierNode, DelegatingNode(), CompositionLocalConsumerModifierNode {
+) :
+    PointerInputModifierNode,
+    DelegatingNode(),
+    CompositionLocalConsumerModifierNode,
+    ObserverModifierNode {
     private val pointerInputHandler: suspend PointerInputScope.() -> Unit = { pointerInput() }
     private val delegate = delegate(SuspendingPointerInputModifierNode(pointerInputHandler))
     private val velocityTracker = VelocityTracker()
+    private var previousEnabled: Boolean = false
 
     var enabled: () -> Boolean = enabled
         set(value) {
@@ -141,6 +148,21 @@ internal class MultiPointerDraggableNode(
             }
         }
 
+    override fun onAttach() {
+        previousEnabled = enabled()
+        onObservedReadsChanged()
+    }
+
+    override fun onObservedReadsChanged() {
+        observeReads {
+            val newEnabled = enabled()
+            if (newEnabled != previousEnabled) {
+                delegate.resetPointerInputHandler()
+            }
+            previousEnabled = newEnabled
+        }
+    }
+
     override fun onCancelPointerInput() = delegate.onCancelPointerInput()
 
     override fun onPointerEvent(
diff --git a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt
index 560f3b7c7d53..d81631aad13a 100644
--- a/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt
+++ b/packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SwipeToSceneTest.kt
@@ -21,6 +21,9 @@ import androidx.compose.foundation.layout.Spacer
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.size
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.geometry.Offset
 import androidx.compose.ui.platform.LocalViewConfiguration
@@ -63,7 +66,10 @@ class SwipeToSceneTest {
 
     /** The content under test. */
     @Composable
-    private fun TestContent(layoutState: SceneTransitionLayoutState) {
+    private fun TestContent(
+        layoutState: SceneTransitionLayoutState,
+        swipesEnabled: () -> Boolean = { true },
+    ) {
         SceneTransitionLayout(
             state = layoutState,
             modifier = Modifier.size(LayoutWidth, LayoutHeight).testTag(TestElements.Foo.debugName),
@@ -71,29 +77,35 @@ class SwipeToSceneTest {
             scene(
                 TestScenes.SceneA,
                 userActions =
-                    mapOf(
-                        Swipe.Left to TestScenes.SceneB,
-                        Swipe.Down to TestScenes.SceneC,
-                        Swipe.Up to TestScenes.SceneB,
-                    ),
+                    if (swipesEnabled())
+                        mapOf(
+                            Swipe.Left to TestScenes.SceneB,
+                            Swipe.Down to TestScenes.SceneC,
+                            Swipe.Up to TestScenes.SceneB,
+                        )
+                    else emptyMap(),
             ) {
                 Box(Modifier.fillMaxSize())
             }
             scene(
                 TestScenes.SceneB,
-                userActions = mapOf(Swipe.Right to TestScenes.SceneA),
+                userActions =
+                    if (swipesEnabled()) mapOf(Swipe.Right to TestScenes.SceneA) else emptyMap(),
             ) {
                 Box(Modifier.fillMaxSize())
             }
             scene(
                 TestScenes.SceneC,
                 userActions =
-                    mapOf(
-                        Swipe.Down to TestScenes.SceneA,
-                        Swipe(SwipeDirection.Down, pointerCount = 2) to TestScenes.SceneB,
-                        Swipe(SwipeDirection.Right, fromSource = Edge.Left) to TestScenes.SceneB,
-                        Swipe(SwipeDirection.Down, fromSource = Edge.Top) to TestScenes.SceneB,
-                    ),
+                    if (swipesEnabled())
+                        mapOf(
+                            Swipe.Down to TestScenes.SceneA,
+                            Swipe(SwipeDirection.Down, pointerCount = 2) to TestScenes.SceneB,
+                            Swipe(SwipeDirection.Right, fromSource = Edge.Left) to
+                                TestScenes.SceneB,
+                            Swipe(SwipeDirection.Down, fromSource = Edge.Top) to TestScenes.SceneB,
+                        )
+                    else emptyMap(),
             ) {
                 Box(Modifier.fillMaxSize())
             }
@@ -431,4 +443,36 @@ class SwipeToSceneTest {
         assertThat(transition).isNotNull()
         assertThat(transition?.toScene).isEqualTo(TestScenes.SceneB)
     }
+
+    @Test
+    fun swipeEnabledLater() {
+        val layoutState = MutableSceneTransitionLayoutState(TestScenes.SceneA)
+        var swipesEnabled by mutableStateOf(false)
+        var touchSlop = 0f
+        rule.setContent {
+            touchSlop = LocalViewConfiguration.current.touchSlop
+            TestContent(layoutState, swipesEnabled = { swipesEnabled })
+        }
+
+        // Drag down from the middle. This should not do anything, because swipes are disabled.
+        rule.onRoot().performTouchInput {
+            down(middle)
+            moveBy(Offset(0f, touchSlop), delayMillis = 1_000)
+        }
+        assertThat(layoutState.currentTransition).isNull()
+
+        // Release finger.
+        rule.onRoot().performTouchInput { up() }
+
+        // Enable swipes.
+        swipesEnabled = true
+        rule.waitForIdle()
+
+        // Drag down from the middle. Now it should start a transition.
+        rule.onRoot().performTouchInput {
+            down(middle)
+            moveBy(Offset(0f, touchSlop), delayMillis = 1_000)
+        }
+        assertThat(layoutState.currentTransition).isNotNull()
+    }
 }