Rename EmittedOutput to WorkflowOutput, move to workflow-core.

workflow-core/api/workflow-core.api

@@ -222,7 +222,7 @@ public final class com/squareup/workflow/WorkflowActionKt {
 	public static final fun action (Ljava/lang/String;Lkotlin/jvm/functions/Function1;)Lcom/squareup/workflow/WorkflowAction;
 	public static final fun action (Lkotlin/jvm/functions/Function0;Lkotlin/jvm/functions/Function1;)Lcom/squareup/workflow/WorkflowAction;
 	public static synthetic fun action$default (Ljava/lang/String;Lkotlin/jvm/functions/Function1;ILjava/lang/Object;)Lcom/squareup/workflow/WorkflowAction;
-	public static final fun applyTo (Lcom/squareup/workflow/WorkflowAction;Ljava/lang/Object;Lkotlin/jvm/functions/Function1;)Lkotlin/Pair;
+	public static final fun applyTo (Lcom/squareup/workflow/WorkflowAction;Ljava/lang/Object;)Lkotlin/Pair;
 }
 
 public final class com/squareup/workflow/WorkflowIdentifier {
@@ -245,3 +245,11 @@ public final class com/squareup/workflow/WorkflowKt {
 	public static final fun mapRendering (Lcom/squareup/workflow/Workflow;Lkotlin/jvm/functions/Function1;)Lcom/squareup/workflow/Workflow;
 }
 
+public final class com/squareup/workflow/WorkflowOutput {
+	public fun <init> (Ljava/lang/Object;)V
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getValue ()Ljava/lang/Object;
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+

workflow-core/src/main/java/com/squareup/workflow/WorkflowAction.kt

@@ -32,21 +32,16 @@ interface WorkflowAction<StateT, out OutputT> {
    * @param nextState the state that the workflow should move to. Default is the current state.
    */
   class Updater<S, in O>(var nextState: S) {
-    private var output: @UnsafeVariance O? = null
-    private var isOutputSet = false
+    internal var output: WorkflowOutput<@UnsafeVariance O>? = null
+      private set
 
     /**
      * Sets the value the workflow will emit as output when this action is applied.
      * If this method is not called, there will be no output.
      */
     fun setOutput(output: O) {
-      this.output = output
-      isOutputSet = true
+      this.output = WorkflowOutput(output)
     }
-
-    @Suppress("UNCHECKED_CAST")
-    internal fun <T : Any> mapOutput(mapper: (@UnsafeVariance O) -> T): T? =
-      if (isOutputSet) mapper(output as O) else null
   }
 
   /**
@@ -211,19 +206,25 @@ inline fun <StateT, OutputT> action(
   override fun toString(): String = "WorkflowAction(${name()})@${hashCode()}"
 }
 
-/**
- * Applies this [WorkflowAction] to [state]. If the action sets an output, the output will be
- * transformed by [mapOutput], and then both the new state and the transformed output will be
- * returned.
- *
- * If the action sets the output multiple times, only the last one will be used.
- */
-fun <StateT, OutputT, T : Any> WorkflowAction<StateT, OutputT>.applyTo(
-  state: StateT,
-  mapOutput: (OutputT) -> T
-): Pair<StateT, T?> {
+/** Applies this [WorkflowAction] to [state]. */
+@ExperimentalWorkflowApi
+fun <StateT, OutputT> WorkflowAction<StateT, OutputT>.applyTo(
+  state: StateT
+): Pair<StateT, WorkflowOutput<OutputT>?> {
   val updater = Updater<StateT, OutputT>(state)
   updater.apply()
-  val output = updater.mapOutput(mapOutput)
-  return Pair(updater.nextState, output)
+  return Pair(updater.nextState, updater.output)
+}
+
+/** Wrapper around a potentially-nullable [OutputT] value. */
+class WorkflowOutput<out OutputT>(val value: OutputT) {
+  override fun toString(): String = "WorkflowOutput($value)"
+
+  override fun equals(other: Any?): Boolean = when {
+    this === other -> true
+    other !is WorkflowOutput<*> -> false
+    else -> value == other.value
+  }
+
+  override fun hashCode(): Int = value.hashCode()
 }

workflow-core/src/test/java/com/squareup/workflow/SinkTest.kt

@@ -22,7 +22,6 @@ import kotlinx.coroutines.test.runBlockingTest
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFalse
-import kotlin.test.assertNotNull
 import kotlin.test.assertNull
 import kotlin.test.assertTrue
 import kotlin.test.fail
@@ -52,11 +51,9 @@ class SinkTest {
       assertEquals(1, sink.actions.size)
       sink.actions.removeFirst()
           .let { action ->
-            val (newState, output) = action.applyTo("state") {
-              assertEquals("output: 1", it)
-            }
+            val (newState, output) = action.applyTo("state")
             assertEquals("state 1", newState)
-            assertNotNull(output)
+            assertEquals("output: 1", output?.value)
           }
       assertTrue(sink.actions.isEmpty())
 
@@ -65,11 +62,9 @@ class SinkTest {
       assertEquals(1, sink.actions.size)
       sink.actions.removeFirst()
           .let { action ->
-            val (newState, output) = action.applyTo("state") {
-              assertEquals("output: 2", it)
-            }
+            val (newState, output) = action.applyTo("state")
             assertEquals("state 2", newState)
-            assertNotNull(output)
+            assertEquals("output: 2", output?.value)
           }
 
       collector.cancel()
@@ -89,12 +84,10 @@ class SinkTest {
       advanceUntilIdle()
 
       val enqueuedAction = sink.actions.removeFirst()
-      val (newState, output) = enqueuedAction.applyTo("state") {
-        assertEquals("output", it)
-      }
+      val (newState, output) = enqueuedAction.applyTo("state")
       assertEquals(1, applications)
       assertEquals("state applied", newState)
-      assertNotNull(output)
+      assertEquals("output", output?.value)
     }
   }
 
@@ -114,7 +107,7 @@ class SinkTest {
 
       val enqueuedAction = sink.actions.removeFirst()
       pauseDispatcher()
-      enqueuedAction.applyTo("state") {}
+      enqueuedAction.applyTo("state")
 
       assertFalse(resumed)
       resumeDispatcher()
@@ -138,7 +131,7 @@ class SinkTest {
       val enqueuedAction = sink.actions.removeFirst()
       sendJob.cancel()
       advanceUntilIdle()
-      val (newState, output) = enqueuedAction.applyTo("ignored") {}
+      val (newState, output) = enqueuedAction.applyTo("ignored")
 
       assertFalse(applied)
       assertEquals("ignored", newState)

workflow-core/src/test/java/com/squareup/workflow/WorkflowActionTest.kt

@@ -21,6 +21,7 @@ import kotlin.test.assertEquals
 import kotlin.test.assertNotNull
 import kotlin.test.assertNull
 
+@OptIn(ExperimentalWorkflowApi::class)
 class WorkflowActionTest {
 
   @Test fun `applyTo works when no output is set`() {
@@ -29,7 +30,7 @@ class WorkflowActionTest {
         nextState = "nextState: $nextState"
       }
     }
-    val (nextState, output) = action.applyTo("state", ::OutputHolder)
+    val (nextState, output) = action.applyTo("state")
     assertEquals("nextState: state", nextState)
     assertNull(output)
   }
@@ -41,7 +42,7 @@ class WorkflowActionTest {
         setOutput(null)
       }
     }
-    val (nextState, output) = action.applyTo("state", ::OutputHolder)
+    val (nextState, output) = action.applyTo("state")
     assertEquals("nextState: state", nextState)
     assertNotNull(output)
     assertNull(output.value)
@@ -54,40 +55,9 @@ class WorkflowActionTest {
         setOutput("output")
       }
     }
-    val (nextState, output) = action.applyTo("state", ::OutputHolder)
+    val (nextState, output) = action.applyTo("state")
     assertEquals("nextState: state", nextState)
     assertNotNull(output)
     assertEquals("output", output.value)
   }
-
-  @Test fun `applyTo doens't invoke mapOutput when output is not set`() {
-    val action = object : WorkflowAction<String, String?> {
-      override fun Updater<String, String?>.apply() {
-        nextState = "nextState: $nextState"
-      }
-    }
-    var outputCalls = 0
-    val (nextState, output) = action.applyTo("state") { outputCalls++ }
-    assertEquals("nextState: state", nextState)
-    assertNull(output)
-    assertEquals(0, outputCalls)
-  }
-
-  @Test fun `applyTo only invokes mapOutput once when output is set multiple times`() {
-    val action = object : WorkflowAction<String, String?> {
-      override fun Updater<String, String?>.apply() {
-        setOutput("first output")
-        nextState = "nextState: $nextState"
-        setOutput(null)
-        setOutput("third output")
-      }
-    }
-    val outputs = mutableListOf<String?>()
-    val (nextState, output) = action.applyTo("state") { outputs += it }
-    assertEquals("nextState: state", nextState)
-    assertNotNull(output)
-    assertEquals(listOf<String?>("third output"), outputs)
-  }
-
-  private data class OutputHolder<O>(val value: O)
 }

workflow-runtime/src/main/java/com/squareup/workflow/RenderWorkflow.kt

@@ -163,7 +163,7 @@ fun <PropsT, OutputT, RenderingT> renderWorkflowIn(
         // After receiving an output, the next render pass must be done before emitting that output,
         // so that the workflow states appear consistent to observers of the outputs and renderings.
         renderingsAndSnapshots.value = runner.nextRendering()
-        output.withValue { onOutput(it) }
+        output?.let { onOutput(it.value) }
       }
   }
 

workflow-runtime/src/main/java/com/squareup/workflow/internal/SubtreeManager.kt

@@ -22,6 +22,7 @@ import com.squareup.workflow.Workflow
 import com.squareup.workflow.WorkflowAction
 import com.squareup.workflow.WorkflowInterceptor
 import com.squareup.workflow.WorkflowInterceptor.WorkflowSession
+import com.squareup.workflow.WorkflowOutput
 import kotlinx.coroutines.selects.SelectBuilder
 import kotlin.coroutines.CoroutineContext
 import kotlin.coroutines.EmptyCoroutineContext
@@ -98,7 +99,7 @@ import kotlin.coroutines.EmptyCoroutineContext
 internal class SubtreeManager<StateT, OutputT>(
   snapshotCache: Map<WorkflowNodeId, TreeSnapshot>,
   private val contextForChildren: CoroutineContext,
-  private val emitActionToParent: (WorkflowAction<StateT, OutputT>) -> MaybeOutput<Any?>,
+  private val emitActionToParent: (WorkflowAction<StateT, OutputT>) -> WorkflowOutput<Any?>?,
   private val workflowSession: WorkflowSession? = null,
   private val interceptor: WorkflowInterceptor = NoopWorkflowInterceptor,
   private val idCounter: IdCounter? = null,
@@ -158,7 +159,7 @@ internal class SubtreeManager<StateT, OutputT>(
    * Uses [selector] to invoke [WorkflowNode.tick] for every running child workflow this instance
    * is managing.
    */
-  fun <T> tickChildren(selector: SelectBuilder<MaybeOutput<T>>) {
+  fun <T> tickChildren(selector: SelectBuilder<WorkflowOutput<T>?>) {
     children.forEachActive { child ->
       child.workflowNode.tick(selector)
     }
@@ -182,7 +183,7 @@ internal class SubtreeManager<StateT, OutputT>(
     val id = child.id(key)
     lateinit var node: WorkflowChildNode<ChildPropsT, ChildOutputT, StateT, OutputT>
 
-    fun acceptChildOutput(output: ChildOutputT): MaybeOutput<Any?> {
+    fun acceptChildOutput(output: ChildOutputT): WorkflowOutput<Any?>? {
       val action = node.acceptChildOutput(output)
       return emitActionToParent(action)
     }

workflow-runtime/src/main/java/com/squareup/workflow/internal/WorkflowNode.kt

@@ -25,6 +25,7 @@ import com.squareup.workflow.WorkflowAction
 import com.squareup.workflow.WorkflowIdentifier
 import com.squareup.workflow.WorkflowInterceptor
 import com.squareup.workflow.WorkflowInterceptor.WorkflowSession
+import com.squareup.workflow.WorkflowOutput
 import com.squareup.workflow.applyTo
 import com.squareup.workflow.intercept
 import com.squareup.workflow.internal.RealRenderContext.SideEffectRunner
@@ -60,7 +61,7 @@ internal class WorkflowNode<PropsT, StateT, OutputT, RenderingT>(
   initialProps: PropsT,
   snapshot: TreeSnapshot,
   baseContext: CoroutineContext,
-  private val emitOutputToParent: (OutputT) -> MaybeOutput<Any?> = { MaybeOutput.of(it) },
+  private val emitOutputToParent: (OutputT) -> WorkflowOutput<Any?>? = { WorkflowOutput(it) },
   override val parent: WorkflowSession? = null,
   private val interceptor: WorkflowInterceptor = NoopWorkflowInterceptor,
   idCounter: IdCounter? = null,
@@ -183,7 +184,7 @@ internal class WorkflowNode<PropsT, StateT, OutputT, RenderingT>(
    *
    * It is an error to call this method after calling [cancel].
    */
-  fun <T> tick(selector: SelectBuilder<MaybeOutput<T>>) {
+  fun <T> tick(selector: SelectBuilder<WorkflowOutput<T>?>) {
     // Listen for any child workflow updates.
     subtreeManager.tickChildren(selector)
 
@@ -198,7 +199,7 @@ internal class WorkflowNode<PropsT, StateT, OutputT, RenderingT>(
             // Set the tombstone flag so we don't continue to listen to the subscription.
             child.tombstone = true
             // Nothing to do on close other than update the session, so don't emit any output.
-            return@onReceive MaybeOutput.none()
+            return@onReceive null
           } else {
             val update = child.acceptUpdate(valueOrDone.value)
             @Suppress("UNCHECKED_CAST")
@@ -277,11 +278,11 @@ internal class WorkflowNode<PropsT, StateT, OutputT, RenderingT>(
    * Applies [action] to this workflow's [state] and
    * [emits an output to its parent][emitOutputToParent] if necessary.
    */
-  private fun <T> applyAction(action: WorkflowAction<StateT, OutputT>): MaybeOutput<T> {
-    val (newState, tickResult) = action.applyTo(state, emitOutputToParent)
+  private fun <T> applyAction(action: WorkflowAction<StateT, OutputT>): WorkflowOutput<T>? {
+    val (newState, tickResult) = action.applyTo(state)
     state = newState
     @Suppress("UNCHECKED_CAST")
-    return (tickResult ?: MaybeOutput.none()) as MaybeOutput<T>
+    return tickResult?.let { emitOutputToParent(it.value) } as WorkflowOutput<T>?
   }
 
   private fun <T> createWorkerNode(

workflow-runtime/src/main/java/com/squareup/workflow/internal/WorkflowRunner.kt

@@ -20,6 +20,7 @@ import com.squareup.workflow.RenderingAndSnapshot
 import com.squareup.workflow.TreeSnapshot
 import com.squareup.workflow.Workflow
 import com.squareup.workflow.WorkflowInterceptor
+import com.squareup.workflow.WorkflowOutput
 import kotlinx.coroutines.CancellationException
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.ExperimentalCoroutinesApi
@@ -83,7 +84,7 @@ internal class WorkflowRunner<PropsT, OutputT, RenderingT>(
 
   // Tick _might_ return an output, but if it returns null, it means the state or a child
   // probably changed, so we should re-render/snapshot and emit again.
-  suspend fun nextOutput(): MaybeOutput<OutputT> = select {
+  suspend fun nextOutput(): WorkflowOutput<OutputT>? = select {
     // Stop trying to read from the inputs channel after it's closed.
     if (!propsChannel.isClosedForReceive) {
       // TODO(https://github.com/square/workflow/issues/512) Replace with receiveOrClosed.
@@ -95,7 +96,7 @@ internal class WorkflowRunner<PropsT, OutputT, RenderingT>(
           }
         }
         // Return null to tell the caller to do another render pass, but not emit an output.
-        return@onReceiveOrNull MaybeOutput.none()
+        return@onReceiveOrNull null
       }
     }