Introduce renderComposable.

samples/compose-samples/src/main/java/com/squareup/sample/compose/nestedrenderings/NestedRenderingsActivity.kt

@@ -10,6 +10,7 @@ import androidx.compose.ui.graphics.Color
 import androidx.lifecycle.SavedStateHandle
 import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
+import com.squareup.workflow1.SimpleLoggingWorkflowInterceptor
 import com.squareup.workflow1.WorkflowExperimentalRuntime
 import com.squareup.workflow1.config.AndroidRuntimeConfigTools
 import com.squareup.workflow1.mapRendering
@@ -47,7 +48,8 @@ class NestedRenderingsActivity : AppCompatActivity() {
         workflow = RecursiveWorkflow.mapRendering { it.withEnvironment(viewEnvironment) },
         scope = viewModelScope,
         savedStateHandle = savedState,
-        runtimeConfig = AndroidRuntimeConfigTools.getAppWorkflowRuntimeConfig()
+        runtimeConfig = AndroidRuntimeConfigTools.getAppWorkflowRuntimeConfig(),
+        interceptors = listOf(SimpleLoggingWorkflowInterceptor())
       )
     }
   }

settings.gradle.kts

@@ -7,6 +7,7 @@ pluginManagement {
     google()
     // For binary compatibility validator.
     maven { url = uri("https://kotlin.bintray.com/kotlinx") }
+    maven("https://maven.pkg.jetbrains.space/public/p/compose/dev")
   }
   includeBuild("build-logic")
 }

workflow-core/build.gradle.kts

@@ -3,6 +3,7 @@ import com.squareup.workflow1.buildsrc.iosWithSimulatorArm64
 plugins {
   id("kotlin-multiplatform")
   id("published")
+  id("org.jetbrains.compose") version "1.7.3"
 }
 
 kotlin {
@@ -23,6 +24,8 @@ dependencies {
   commonMainApi(libs.kotlinx.coroutines.core)
   // For Snapshot.
   commonMainApi(libs.squareup.okio)
+  commonMainApi("org.jetbrains.compose.runtime:runtime:1.7.3")
+  commonMainApi("org.jetbrains.compose.runtime:runtime-saveable:1.7.3")
 
   commonTestImplementation(libs.kotlinx.atomicfu)
   commonTestImplementation(libs.kotlinx.coroutines.test.common)

workflow-core/src/commonMain/kotlin/com/squareup/workflow1/BaseRenderContext.kt

@@ -209,6 +209,20 @@ public fun <PropsT, StateT, OutputT, ChildRenderingT>
   key: String = ""
 ): ChildRenderingT = renderChild(child, Unit, key) { noAction() }
 
+// /**
+//  * TODO
+//  */
+// @WorkflowExperimentalApi
+// public fun <PropsT, StateT, OutputT, ChildRenderingT>
+//   BaseRenderContext<PropsT, StateT, OutputT>.renderComposable(
+//   key: String = "",
+//   content: @WorkflowComposable @Composable () -> ChildRenderingT
+// ): ChildRenderingT = renderComposable<Nothing, ChildRenderingT>(
+//   key = key,
+//   handler = { noAction() },
+//   content = { content() }
+// )
+
 /**
  * Ensures a [LifecycleWorker] is running. Since [worker] can't emit anything,
  * it can't trigger any [WorkflowAction]s.

workflow-core/src/commonMain/kotlin/com/squareup/workflow1/IdCacheable.kt

@@ -1,9 +1,12 @@
 package com.squareup.workflow1
 
+import com.squareup.workflow1.compose.ComposeWorkflow
+
 /**
  * If your Workflow caches its [WorkflowIdentifier] (to avoid frequent lookups) then implement
- * this interface. Note that [StatefulWorkflow] and [StatelessWorkflow] already implement this,
- * so you only need to do so if you do not extend one of those classes.
+ * this interface. Note that built-in workflow types ([StatefulWorkflow], [StatelessWorkflow],
+ * [ComposeWorkflow] etc.) already implement this, so you only need to do so if you do not extend
+ * one of those classes.
  *
  * Your Workflow can just assign null to this value as the [identifier] extension will use it
  * for caching.

workflow-core/src/commonMain/kotlin/com/squareup/workflow1/StatefulWorkflow.kt

@@ -5,6 +5,7 @@
 package com.squareup.workflow1
 
 import com.squareup.workflow1.RuntimeConfigOptions.STABLE_EVENT_HANDLERS
+import com.squareup.workflow1.StatefulWorkflow.RenderContext
 import kotlinx.coroutines.CoroutineScope
 import kotlin.jvm.JvmMultifileClass
 import kotlin.jvm.JvmName

workflow-core/src/commonMain/kotlin/com/squareup/workflow1/compose/ComposeWorkflow.kt

@@ -0,0 +1,33 @@
+package com.squareup.workflow1.compose
+
+import androidx.compose.runtime.Composable
+import com.squareup.workflow1.IdCacheable
+import com.squareup.workflow1.StatefulWorkflow
+import com.squareup.workflow1.Workflow
+import com.squareup.workflow1.WorkflowExperimentalApi
+
+/**
+ * TODO
+ */
+@WorkflowExperimentalApi
+public abstract class ComposeWorkflow<PropsT, OutputT, out RenderingT> :
+  Workflow<PropsT, OutputT, RenderingT>,
+  IdCacheable {
+
+  /**
+   * TODO
+   */
+  @WorkflowComposable
+  @Composable
+  protected abstract fun produceRendering(
+    props: PropsT,
+    emitOutput: (OutputT) -> Unit
+  ): RenderingT
+
+  final override fun asStatefulWorkflow(): StatefulWorkflow<PropsT, *, OutputT, RenderingT> {
+    throw UnsupportedOperationException(
+      "This version of the Compose runtime does not support ComposeWorkflow. " +
+        "Please upgrade your workflow-runtime."
+    )
+  }
+}

workflow-core/src/commonMain/kotlin/com/squareup/workflow1/compose/WorkflowComposable.kt

@@ -0,0 +1,25 @@
+package com.squareup.workflow1.compose
+
+import androidx.compose.runtime.ComposableTargetMarker
+import com.squareup.workflow1.WorkflowExperimentalApi
+import kotlin.annotation.AnnotationRetention.BINARY
+import kotlin.annotation.AnnotationTarget.FILE
+import kotlin.annotation.AnnotationTarget.FUNCTION
+import kotlin.annotation.AnnotationTarget.PROPERTY_GETTER
+import kotlin.annotation.AnnotationTarget.TYPE
+import kotlin.annotation.AnnotationTarget.TYPE_PARAMETER
+
+/**
+ * An annotation that can be used to mark a composable function as being expected to be use in a
+ * composable function that is also marked or inferred to be marked as a [WorkflowComposable], i.e.
+ * that can be called from [BaseRenderContext.renderComposable].
+ *
+ * Using this annotation explicitly is rarely necessary as the Compose compiler plugin will infer
+ * the necessary equivalent annotations automatically. See
+ * [androidx.compose.runtime.ComposableTarget] for details.
+ */
+@WorkflowExperimentalApi
+@ComposableTargetMarker(description = "Workflow Composable")
+@Target(FILE, FUNCTION, PROPERTY_GETTER, TYPE, TYPE_PARAMETER)
+@Retention(BINARY)
+public annotation class WorkflowComposable

workflow-runtime/build.gradle.kts

@@ -3,6 +3,7 @@ import com.squareup.workflow1.buildsrc.iosWithSimulatorArm64
 plugins {
   id("kotlin-multiplatform")
   id("published")
+  id("org.jetbrains.compose") version "1.7.3"
 }
 
 kotlin {
@@ -16,6 +17,13 @@ kotlin {
   if (targets == "kmp" || targets == "js") {
     js(IR) { browser() }
   }
+  // sourceSets {
+  //   getByName("commonMain") {
+  //     dependencies {
+  //       implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.8.1")
+  //     }
+  //   }
+  // }
 }
 
 dependencies {

workflow-runtime/src/commonMain/kotlin/com/squareup/workflow1/RenderWorkflow.kt

@@ -7,6 +7,7 @@ import com.squareup.workflow1.WorkflowInterceptor.RenderPassesComplete
 import com.squareup.workflow1.internal.WorkflowRunner
 import com.squareup.workflow1.internal.chained
 import kotlinx.coroutines.CancellationException
+import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Job
 import kotlinx.coroutines.flow.Flow

workflow-runtime/src/commonMain/kotlin/com/squareup/workflow1/WorkflowInterceptor.kt

@@ -1,6 +1,9 @@
+@file:OptIn(WorkflowExperimentalApi::class)
+
 package com.squareup.workflow1
 
 import com.squareup.workflow1.WorkflowInterceptor.RenderContextInterceptor
+import com.squareup.workflow1.WorkflowInterceptor.RuntimeLoopOutcome
 import com.squareup.workflow1.WorkflowInterceptor.WorkflowSession
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Job
@@ -430,6 +433,21 @@ private class InterceptedRenderContext<P, S, O>(
       baseRenderContext.renderChild(iChild, iProps, iKey, iHandler)
     }
 
+  // override fun <ChildPropsT, ChildOutputT, ChildRenderingT> renderChild(
+  //   child: ComposeWorkflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
+  //   props: ChildPropsT,
+  //   key: String,
+  //   handler: (ChildOutputT) -> WorkflowAction<P, S, O>
+  // ): ChildRenderingT =
+  //   interceptor.onRenderChild(child, props, key, handler) { iChild, iProps, iKey, iHandler ->
+  //     // Explicitly dispatch to the ComposeWorkflow overload if necessary.
+  //     if (iChild is ComposeWorkflow) {
+  //       baseRenderContext.renderChild(iChild, iProps, iKey, iHandler)
+  //     } else {
+  //       baseRenderContext.renderChild(iChild, iProps, iKey, iHandler)
+  //     }
+  //   }
+
   override fun runningSideEffect(
     key: String,
     sideEffect: suspend CoroutineScope.() -> Unit
@@ -459,6 +477,23 @@ private class InterceptedRenderContext<P, S, O>(
     }
   }
 
+  // @OptIn(WorkflowExperimentalApi::class)
+  // override fun <ChildOutputT, ChildRenderingT> renderComposable(
+  //   key: String,
+  //   handler: (ChildOutputT) -> WorkflowAction<P, S, O>,
+  //   content: @WorkflowComposable @Composable (emitOutput: (ChildOutputT) -> Unit) -> ChildRenderingT
+  // ): ChildRenderingT = interceptor.onRenderComposable(
+  //   key = key,
+  //   content = content,
+  //   proceed = { iKey, iContent ->
+  //     baseRenderContext.renderComposable(
+  //       key = iKey,
+  //       handler = handler,
+  //       content = iContent
+  //     )
+  //   }
+  // )
+
   /**
    * In a block with a CoroutineScope receiver, calls to `coroutineContext` bind
    * to `CoroutineScope.coroutineContext` instead of `suspend val coroutineContext`.