Remove non-null upper bound for OutputT.

Fixes #59.

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/Pair;
+	public static final fun applyTo (Lcom/squareup/workflow/WorkflowAction;Ljava/lang/Object;Lkotlin/jvm/functions/Function1;)Lkotlin/Pair;
 }
 
 public final class com/squareup/workflow/WorkflowIdentifier {

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

@@ -51,7 +51,7 @@ import com.squareup.workflow.WorkflowAction.Updater
  *
  * See [renderChild].
  */
-interface RenderContext<StateT, in OutputT : Any> {
+interface RenderContext<StateT, in OutputT> {
 
   /**
    * Accepts a single [WorkflowAction], invokes that action by calling [WorkflowAction.apply]
@@ -94,7 +94,7 @@ interface RenderContext<StateT, in OutputT : Any> {
    * @param key An optional string key that is used to distinguish between workflows of the same
    * type.
    */
-  fun <ChildPropsT, ChildOutputT : Any, ChildRenderingT> renderChild(
+  fun <ChildPropsT, ChildOutputT, ChildRenderingT> renderChild(
     child: Workflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
     props: ChildPropsT,
     key: String = "",
@@ -144,7 +144,7 @@ interface RenderContext<StateT, in OutputT : Any> {
  * Convenience alias of [RenderContext.renderChild] for workflows that don't take props.
  */
 /* ktlint-disable parameter-list-wrapping */
-fun <StateT, OutputT : Any, ChildOutputT : Any, ChildRenderingT>
+fun <StateT, OutputT, ChildOutputT, ChildRenderingT>
     RenderContext<StateT, OutputT>.renderChild(
   child: Workflow<Unit, ChildOutputT, ChildRenderingT>,
   key: String = "",
@@ -157,7 +157,7 @@ fun <StateT, OutputT : Any, ChildOutputT : Any, ChildRenderingT>
  * output.
  */
 /* ktlint-disable parameter-list-wrapping */
-fun <PropsT, StateT, OutputT : Any, ChildRenderingT>
+fun <PropsT, StateT, OutputT, ChildRenderingT>
     RenderContext<StateT, OutputT>.renderChild(
   child: Workflow<PropsT, Nothing, ChildRenderingT>,
   props: PropsT,
@@ -170,7 +170,7 @@ fun <PropsT, StateT, OutputT : Any, ChildRenderingT>
  * output.
  */
 /* ktlint-disable parameter-list-wrapping */
-fun <StateT, OutputT : Any, ChildRenderingT>
+fun <StateT, OutputT, ChildRenderingT>
     RenderContext<StateT, OutputT>.renderChild(
   child: Workflow<Unit, Nothing, ChildRenderingT>,
   key: String = ""
@@ -185,7 +185,7 @@ fun <StateT, OutputT : Any, ChildRenderingT>
  *
  * @param key An optional string key that is used to distinguish between identical [Worker]s.
  */
-fun <StateT, OutputT : Any> RenderContext<StateT, OutputT>.runningWorker(
+fun <StateT, OutputT> RenderContext<StateT, OutputT>.runningWorker(
   worker: Worker<Nothing>,
   key: String = ""
 ) {
@@ -199,7 +199,7 @@ fun <StateT, OutputT : Any> RenderContext<StateT, OutputT>.runningWorker(
  * Alternative to [RenderContext.actionSink] that allows externally defined
  * event types to be mapped to anonymous [WorkflowAction]s.
  */
-fun <EventT, StateT, OutputT : Any> RenderContext<StateT, OutputT>.makeEventSink(
+fun <EventT, StateT, OutputT> RenderContext<StateT, OutputT>.makeEventSink(
   update: Updater<StateT, OutputT>.(EventT) -> Unit
 ): Sink<EventT> = actionSink.contraMap { event ->
   action({ "eventSink($event)" }) { update(event) }
@@ -216,7 +216,7 @@ fun <EventT, StateT, OutputT : Any> RenderContext<StateT, OutputT>.makeEventSink
     "Use runningWorker",
     ReplaceWith("runningWorker(worker, key, handler)", "com.squareup.workflow.runningWorker")
 )
-fun <StateT, OutputT : Any, T> RenderContext<StateT, OutputT>.onWorkerOutput(
+fun <StateT, OutputT, T> RenderContext<StateT, OutputT>.onWorkerOutput(
   worker: Worker<T>,
   key: String = "",
   handler: (T) -> WorkflowAction<StateT, OutputT>

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

@@ -71,7 +71,7 @@ fun <T1, T2> Sink<T1>.contraMap(transform: (T2) -> T1): Sink<T2> {
  * ```
  */
 @ExperimentalWorkflowApi
-suspend fun <T, StateT, OutputT : Any> Flow<T>.collectToSink(
+suspend fun <T, StateT, OutputT> Flow<T>.collectToSink(
   actionSink: Sink<WorkflowAction<StateT, OutputT>>,
   handler: (T) -> WorkflowAction<StateT, OutputT>
 ) {
@@ -93,7 +93,7 @@ suspend fun <T, StateT, OutputT : Any> Flow<T>.collectToSink(
  * This method is intended to be used from [RenderContext.runningSideEffect].
  */
 @ExperimentalWorkflowApi
-suspend fun <StateT, OutputT : Any> Sink<WorkflowAction<StateT, OutputT>>.sendAndAwaitApplication(
+suspend fun <StateT, OutputT> Sink<WorkflowAction<StateT, OutputT>>.sendAndAwaitApplication(
   action: WorkflowAction<StateT, OutputT>
 ) {
   suspendCancellableCoroutine<Unit> { continuation ->

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

@@ -79,7 +79,7 @@ import com.squareup.workflow.WorkflowAction.Updater
 abstract class StatefulWorkflow<
     in PropsT,
     StateT,
-    out OutputT : Any,
+    out OutputT,
     out RenderingT
     > : Workflow<PropsT, OutputT, RenderingT> {
 
@@ -164,7 +164,7 @@ abstract class StatefulWorkflow<
 /**
  * Returns a stateful [Workflow] implemented via the given functions.
  */
-inline fun <PropsT, StateT, OutputT : Any, RenderingT> Workflow.Companion.stateful(
+inline fun <PropsT, StateT, OutputT, RenderingT> Workflow.Companion.stateful(
   crossinline initialState: (PropsT, Snapshot?) -> StateT,
   crossinline render: RenderContext<StateT, OutputT>.(props: PropsT, state: StateT) -> RenderingT,
   crossinline snapshot: (StateT) -> Snapshot,
@@ -198,7 +198,7 @@ inline fun <PropsT, StateT, OutputT : Any, RenderingT> Workflow.Companion.statef
 /**
  * Returns a stateful [Workflow], with no props, implemented via the given functions.
  */
-inline fun <StateT, OutputT : Any, RenderingT> Workflow.Companion.stateful(
+inline fun <StateT, OutputT, RenderingT> Workflow.Companion.stateful(
   crossinline initialState: (Snapshot?) -> StateT,
   crossinline render: RenderContext<StateT, OutputT>.(state: StateT) -> RenderingT,
   crossinline snapshot: (StateT) -> Snapshot
@@ -213,7 +213,7 @@ inline fun <StateT, OutputT : Any, RenderingT> Workflow.Companion.stateful(
  *
  * This overload does not support snapshotting, but there are other overloads that do.
  */
-inline fun <PropsT, StateT, OutputT : Any, RenderingT> Workflow.Companion.stateful(
+inline fun <PropsT, StateT, OutputT, RenderingT> Workflow.Companion.stateful(
   crossinline initialState: (PropsT) -> StateT,
   crossinline render: RenderContext<StateT, OutputT>.(props: PropsT, state: StateT) -> RenderingT,
   crossinline onPropsChanged: (
@@ -233,7 +233,7 @@ inline fun <PropsT, StateT, OutputT : Any, RenderingT> Workflow.Companion.statef
  *
  * This overload does not support snapshots, but there are others that do.
  */
-inline fun <StateT, OutputT : Any, RenderingT> Workflow.Companion.stateful(
+inline fun <StateT, OutputT, RenderingT> Workflow.Companion.stateful(
   initialState: StateT,
   crossinline render: RenderContext<StateT, OutputT>.(state: StateT) -> RenderingT
 ): StatefulWorkflow<Unit, StateT, OutputT, RenderingT> = stateful(
@@ -249,7 +249,7 @@ inline fun <StateT, OutputT : Any, RenderingT> Workflow.Companion.stateful(
  * @param name A string describing the update for debugging, included in [toString].
  * @param update Function that defines the workflow update.
  */
-fun <PropsT, StateT, OutputT : Any, RenderingT>
+fun <PropsT, StateT, OutputT, RenderingT>
     StatefulWorkflow<PropsT, StateT, OutputT, RenderingT>.action(
       name: String = "",
       update: Updater<StateT, OutputT>.() -> Unit
@@ -264,7 +264,7 @@ fun <PropsT, StateT, OutputT : Any, RenderingT>
  * in [toString].
  * @param update Function that defines the workflow update.
  */
-fun <PropsT, StateT, OutputT : Any, RenderingT>
+fun <PropsT, StateT, OutputT, RenderingT>
     StatefulWorkflow<PropsT, StateT, OutputT, RenderingT>.action(
       name: () -> String,
       update: Updater<StateT, OutputT>.() -> Unit
@@ -280,7 +280,7 @@ fun <PropsT, StateT, OutputT : Any, RenderingT>
         imports = arrayOf("com.squareup.workflow.action")
     )
 )
-fun <PropsT, StateT, OutputT : Any, RenderingT>
+fun <PropsT, StateT, OutputT, RenderingT>
     StatefulWorkflow<PropsT, StateT, OutputT, RenderingT>.workflowAction(
       name: String = "",
       block: Mutator<StateT>.() -> OutputT?
@@ -294,7 +294,7 @@ fun <PropsT, StateT, OutputT : Any, RenderingT>
         imports = arrayOf("com.squareup.workflow.action")
     )
 )
-fun <PropsT, StateT, OutputT : Any, RenderingT>
+fun <PropsT, StateT, OutputT, RenderingT>
     StatefulWorkflow<PropsT, StateT, OutputT, RenderingT>.workflowAction(
       name: () -> String,
       block: Mutator<StateT>.() -> OutputT?

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

@@ -34,7 +34,7 @@ import com.squareup.workflow.WorkflowAction.Updater
  *
  * @see StatefulWorkflow
  */
-abstract class StatelessWorkflow<in PropsT, out OutputT : Any, out RenderingT> :
+abstract class StatelessWorkflow<in PropsT, out OutputT, out RenderingT> :
     Workflow<PropsT, OutputT, RenderingT> {
 
   @Suppress("UNCHECKED_CAST")
@@ -82,7 +82,7 @@ abstract class StatelessWorkflow<in PropsT, out OutputT : Any, out RenderingT> :
  * [props][PropsT] received from its parent, and it may render child workflows that do have
  * their own internal state.
  */
-inline fun <PropsT, OutputT : Any, RenderingT> Workflow.Companion.stateless(
+inline fun <PropsT, OutputT, RenderingT> Workflow.Companion.stateless(
   crossinline render: RenderContext<Nothing, OutputT>.(props: PropsT) -> RenderingT
 ): Workflow<PropsT, OutputT, RenderingT> =
   object : StatelessWorkflow<PropsT, OutputT, RenderingT>() {
@@ -108,7 +108,7 @@ fun <RenderingT> Workflow.Companion.rendering(
  * @param name A string describing the update for debugging, included in [toString].
  * @param update Function that defines the workflow update.
  */
-fun <PropsT, OutputT : Any, RenderingT>
+fun <PropsT, OutputT, RenderingT>
     StatelessWorkflow<PropsT, OutputT, RenderingT>.action(
   name: String = "",
   update: Updater<Nothing, OutputT>.() -> Unit
@@ -123,7 +123,7 @@ fun <PropsT, OutputT : Any, RenderingT>
  * [toString].
  * @param update Function that defines the workflow update.
  */
-fun <PropsT, OutputT : Any, RenderingT>
+fun <PropsT, OutputT, RenderingT>
     StatelessWorkflow<PropsT, OutputT, RenderingT>.action(
   name: () -> String,
   update: Updater<Nothing, OutputT>.() -> Unit

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

@@ -247,7 +247,7 @@ interface Worker<out OutputT> {
      * The returned [Worker] will equate to any other workers created with any of the [Worker]
      * builder functions that have the same output type.
      */
-    inline fun <reified OutputT : Any> fromNullable(
+    inline fun <reified OutputT> fromNullable(
         // This could be crossinline, but there's a coroutines bug that will cause the coroutine
         // to immediately resume on suspension inside block when it is crossinline.
         // See https://youtrack.jetbrains.com/issue/KT-31197.

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

@@ -104,7 +104,7 @@ package com.squareup.workflow
  * @see StatefulWorkflow
  * @see StatelessWorkflow
  */
-interface Workflow<in PropsT, out OutputT : Any, out RenderingT> {
+interface Workflow<in PropsT, out OutputT, out RenderingT> {
 
   /**
    * Provides a [StatefulWorkflow] view of this workflow. Necessary because [StatefulWorkflow] is
@@ -125,7 +125,7 @@ interface Workflow<in PropsT, out OutputT : Any, out RenderingT> {
  */
 /* ktlint-disable parameter-list-wrapping */
 @OptIn(ExperimentalWorkflowApi::class)
-fun <PropsT, OutputT : Any, FromRenderingT, ToRenderingT>
+fun <PropsT, OutputT, FromRenderingT, ToRenderingT>
     Workflow<PropsT, OutputT, FromRenderingT>.mapRendering(
   transform: (FromRenderingT) -> ToRenderingT
 ): Workflow<PropsT, OutputT, ToRenderingT> =

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

@@ -21,7 +21,7 @@ import com.squareup.workflow.WorkflowAction.Updater
 /**
  * An atomic operation that updates the state of a [Workflow], and also optionally emits an output.
  */
-interface WorkflowAction<StateT, out OutputT : Any> {
+interface WorkflowAction<StateT, out OutputT> {
   @Deprecated("Use Updater")
   class Mutator<S>(var state: S)
 
@@ -31,16 +31,22 @@ interface WorkflowAction<StateT, out OutputT : Any> {
    *
    * @param nextState the state that the workflow should move to. Default is the current state.
    */
-  class Updater<S, in O : Any>(var nextState: S) {
-    internal var output: @UnsafeVariance O? = null
+  class Updater<S, in O>(var nextState: S) {
+    private var output: @UnsafeVariance O? = null
+    private var isOutputSet = false
 
     /**
      * 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
     }
+
+    @Suppress("UNCHECKED_CAST")
+    internal fun <T : Any> mapOutput(mapper: (@UnsafeVariance O) -> T): T? =
+      if (isOutputSet) mapper(output as O) else null
   }
 
   /**
@@ -69,7 +75,7 @@ interface WorkflowAction<StateT, out OutputT : Any> {
      * Use this to, for example, ignore the output of a child workflow or worker.
      */
     @Suppress("UNCHECKED_CAST")
-    fun <StateT, OutputT : Any> noAction(): WorkflowAction<StateT, OutputT> =
+    fun <StateT, OutputT> noAction(): WorkflowAction<StateT, OutputT> =
       NO_ACTION as WorkflowAction<StateT, OutputT>
 
     /**
@@ -83,7 +89,7 @@ interface WorkflowAction<StateT, out OutputT : Any> {
             imports = arrayOf("com.squareup.workflow.action")
         )
     )
-    fun <StateT, OutputT : Any> enterState(
+    fun <StateT, OutputT> enterState(
       newState: StateT,
       emittingOutput: OutputT? = null
     ): WorkflowAction<StateT, OutputT> =
@@ -103,7 +109,7 @@ interface WorkflowAction<StateT, out OutputT : Any> {
             imports = arrayOf("com.squareup.workflow.action")
         )
     )
-    fun <StateT, OutputT : Any> enterState(
+    fun <StateT, OutputT> enterState(
       name: String,
       newState: StateT,
       emittingOutput: OutputT? = null
@@ -123,7 +129,7 @@ interface WorkflowAction<StateT, out OutputT : Any> {
             imports = arrayOf("com.squareup.workflow.action")
         )
     )
-    fun <StateT, OutputT : Any> modifyState(
+    fun <StateT, OutputT> modifyState(
       name: () -> String,
       emittingOutput: OutputT? = null,
       modify: (StateT) -> StateT
@@ -143,7 +149,7 @@ interface WorkflowAction<StateT, out OutputT : Any> {
             imports = arrayOf("com.squareup.workflow.action")
         )
     )
-    fun <StateT, OutputT : Any> emitOutput(output: OutputT): WorkflowAction<StateT, OutputT> =
+    fun <StateT, OutputT> emitOutput(output: OutputT): WorkflowAction<StateT, OutputT> =
       action({ "emitOutput($output)" }) { setOutput(output) }
 
     /**
@@ -156,7 +162,7 @@ interface WorkflowAction<StateT, out OutputT : Any> {
             imports = arrayOf("com.squareup.workflow.action")
         )
     )
-    fun <StateT, OutputT : Any> emitOutput(
+    fun <StateT, OutputT> emitOutput(
       name: String,
       output: OutputT
     ): WorkflowAction<StateT, OutputT> =
@@ -179,7 +185,7 @@ interface WorkflowAction<StateT, out OutputT : Any> {
  * @see StatelessWorkflow.action
  * @see StatefulWorkflow.action
  */
-inline fun <StateT, OutputT : Any> action(
+inline fun <StateT, OutputT> action(
   name: String = "",
   crossinline apply: Updater<StateT, OutputT>.() -> Unit
 ) = action({ name }, apply)
@@ -197,18 +203,27 @@ inline fun <StateT, OutputT : Any> action(
  * @see StatelessWorkflow.action
  * @see StatefulWorkflow.action
  */
-inline fun <StateT, OutputT : Any> action(
+inline fun <StateT, OutputT> action(
   crossinline name: () -> String,
   crossinline apply: Updater<StateT, OutputT>.() -> Unit
 ): WorkflowAction<StateT, OutputT> = object : WorkflowAction<StateT, OutputT> {
   override fun Updater<StateT, OutputT>.apply() = apply.invoke(this)
   override fun toString(): String = "WorkflowAction(${name()})@${hashCode()}"
 }
 
-fun <StateT, OutputT : Any> WorkflowAction<StateT, OutputT>.applyTo(
-  state: StateT
-): Pair<StateT, OutputT?> {
+/**
+ * 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?> {
   val updater = Updater<StateT, OutputT>(state)
   updater.apply()
-  return Pair(updater.nextState, updater.output)
+  val output = updater.mapOutput(mapOutput)
+  return Pair(updater.nextState, output)
 }