Merge "Add MutableSTLState.snapToScene()" into main

packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SceneTransitionLayoutState.kt

@@ -117,6 +117,9 @@ sealed interface MutableSceneTransitionLayoutState : SceneTransitionLayoutState
         coroutineScope: CoroutineScope,
         transitionKey: TransitionKey? = null,
     ): TransitionState.Transition?
+
+    /** Immediately snap to the given [scene]. */
+    fun snapToScene(scene: SceneKey)
 }
 
 /**
@@ -745,6 +748,17 @@ internal class MutableSceneTransitionLayoutStateImpl(
     override fun CoroutineScope.onChangeScene(scene: SceneKey) {
         setTargetScene(scene, coroutineScope = this)
     }
+
+    override fun snapToScene(scene: SceneKey) {
+        // Force finish all transitions.
+        while (currentTransitions.isNotEmpty()) {
+            val transition = transitionStates[0] as TransitionState.Transition
+            finishTransition(transition, transition.currentScene)
+        }
+
+        check(transitionStates.size == 1)
+        transitionStates[0] = TransitionState.Idle(scene)
+    }
 }
 
 private const val TAG = "SceneTransitionLayoutState"

packages/SystemUI/compose/scene/tests/src/com/android/compose/animation/scene/SceneTransitionLayoutStateTest.kt

@@ -635,4 +635,19 @@ class SceneTransitionLayoutStateTest {
             Log.setWtfHandler(originalHandler)
         }
     }
+
+    @Test
+    fun snapToScene() = runMonotonicClockTest {
+        val state = MutableSceneTransitionLayoutState(SceneA)
+
+        // Transition to B.
+        state.setTargetScene(SceneB, coroutineScope = this)
+        val transition = assertThat(state.transitionState).isTransition()
+        assertThat(transition).hasCurrentScene(SceneB)
+
+        // Snap to C.
+        state.snapToScene(SceneC)
+        assertThat(state.transitionState).isIdle()
+        assertThat(state.transitionState).hasCurrentScene(SceneC)
+    }
 }