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WIP Sketching Compose-based workflows.
See https://www.notion.so/block-xyz/Compose-based-Workflows-1a6be352683880b98600dde8e4413fb9?pvs=4
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‎settings.gradle.kts

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

‎workflow-core/build.gradle.kts

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

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

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@@ -9,8 +9,17 @@
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package com.squareup.workflow1
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import androidx.compose.runtime.Composable
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import androidx.compose.runtime.Composition
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import androidx.compose.runtime.CompositionLocalProvider
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import androidx.compose.runtime.MonotonicFrameClock
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import androidx.compose.runtime.Recomposer
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import androidx.compose.runtime.mutableStateOf
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import com.squareup.workflow1.WorkflowAction.Companion.noAction
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import kotlinx.coroutines.CoroutineScope
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import kotlinx.coroutines.CoroutineStart
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import kotlinx.coroutines.launch
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import kotlin.coroutines.EmptyCoroutineContext
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import kotlin.jvm.JvmMultifileClass
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import kotlin.jvm.JvmName
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import kotlin.reflect.KType
@@ -85,6 +94,43 @@ public interface BaseRenderContext<out PropsT, StateT, in OutputT> {
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handler: (ChildOutputT) -> WorkflowAction<PropsT, StateT, OutputT>
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): ChildRenderingT
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/**
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* Synchronously composes a [content] function and returns its rendering. Whenever [content] is
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* invalidated, this workflow will be re-rendered and the [content] recomposed to return its new
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* value.
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*
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* @see ComposeWorkflow
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*/
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public fun <ChildRenderingT> renderComposable(
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key: String = "",
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content: @WorkflowComposable @Composable () -> ChildRenderingT
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): ChildRenderingT {
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val renderer: WorkflowComposableRenderer = TODO()
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val frameClock: MonotonicFrameClock = TODO()
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val coroutineContext = EmptyCoroutineContext + frameClock
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val recomposer = Recomposer(coroutineContext)
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val composition = Composition(UnitApplier, recomposer)
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// TODO I think we need more than a simple UNDISPATCHED start to make this work – we have to
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// pump the dispatcher until the composition is finished.
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CoroutineScope(coroutineContext).launch(start = CoroutineStart.UNDISPATCHED) {
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try {
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recomposer.runRecomposeAndApplyChanges()
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} finally {
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composition.dispose()
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}
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}
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val rendering = mutableStateOf<ChildRenderingT?>(null)
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composition.setContent {
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CompositionLocalProvider(LocalWorkflowComposableRenderer provides renderer) {
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rendering.value = content()
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}
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}
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@Suppress("UNCHECKED_CAST")
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return rendering.value as ChildRenderingT
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}
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/**
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* Ensures [sideEffect] is running with the given [key].
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*

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

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@@ -0,0 +1,52 @@
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package com.squareup.workflow1
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import androidx.compose.runtime.Composable
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import androidx.compose.runtime.Stable
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import androidx.compose.runtime.remember
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/**
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* A [Workflow]-like interface that participates in a workflow tree via its [Rendering] composable.
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*/
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@Stable
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public interface ComposeWorkflow<
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in PropsT,
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out OutputT,
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out RenderingT
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> {
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/**
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* The main composable of this workflow that consumes some [props] from its parent and may emit
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* an output via [emitOutput].
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*
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* Equivalent to [StatefulWorkflow.render].
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*/
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@WorkflowComposable
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@Composable
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fun Rendering(
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props: PropsT,
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emitOutput: (OutputT) -> Unit
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): RenderingT
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}
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fun <
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PropsT, StateT, OutputT,
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ChildPropsT, ChildOutputT, ChildRenderingT
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> BaseRenderContext<PropsT, StateT, OutputT>.renderChild(
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child: ComposeWorkflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
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props: ChildPropsT,
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key: String = "",
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handler: (ChildOutputT) -> WorkflowAction<PropsT, StateT, OutputT>
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): ChildRenderingT = renderComposable(key = key) {
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// Explicitly remember the output function since we know that actionSink is stable even though
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// Compose might not know that.
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val emitOutput: (ChildOutputT) -> Unit = remember(actionSink) {
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{ output ->
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val action = handler(output)
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actionSink.send(action)
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}
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}
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child.Rendering(
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props = props,
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emitOutput = emitOutput
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)
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}

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

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package com.squareup.workflow1
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import androidx.compose.runtime.Applier
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internal object UnitApplier : Applier<Unit> {
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override val current: Unit
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get() = Unit
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override fun clear() {
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}
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override fun down(node: Unit) {
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}
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override fun insertBottomUp(
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index: Int,
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instance: Unit
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) {
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}
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override fun insertTopDown(
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index: Int,
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instance: Unit
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) {
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}
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override fun move(
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from: Int,
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to: Int,
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count: Int
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) {
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}
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override fun remove(
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index: Int,
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count: Int
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) {
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}
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override fun up() {
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}
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}

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

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

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

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package com.squareup.workflow1
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import androidx.compose.runtime.Composable
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import androidx.compose.runtime.MutableState
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import androidx.compose.runtime.mutableStateOf
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import androidx.compose.runtime.remember
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import androidx.compose.runtime.staticCompositionLocalOf
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internal val LocalWorkflowComposableRenderer =
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staticCompositionLocalOf<WorkflowComposableRenderer> { error("No renderer") }
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internal interface WorkflowComposableRenderer {
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@Composable
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fun <ChildPropsT, ChildOutputT, ChildRenderingT> Child(
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workflow: Workflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
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props: ChildPropsT,
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onOutput: ((ChildOutputT) -> Unit)?
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): ChildRenderingT
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}
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/**
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* Renders a child [Workflow] from any [WorkflowComposable] (e.g. a [ComposeWorkflow.Rendering] or
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* [BaseRenderContext.renderComposable]) and returns its rendering.
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*
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* @param handler An optional function that, if non-null, will be called when the child emits an
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* output. If null, the child's outputs will be ignored.
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*/
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@WorkflowComposable
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@Composable
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fun <ChildPropsT, ChildOutputT, ChildRenderingT> Child(
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workflow: Workflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
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props: ChildPropsT,
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onOutput: ((ChildOutputT) -> Unit)?
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): ChildRenderingT {
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val renderer = LocalWorkflowComposableRenderer.current
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return renderer.Child(workflow, props, onOutput)
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}
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@WorkflowComposable
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@Composable
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fun <ChildPropsT, ChildOutputT, ChildRenderingT> Child(
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workflow: ComposeWorkflow<ChildPropsT, ChildOutputT, ChildRenderingT>,
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props: ChildPropsT,
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handler: ((ChildOutputT) -> Unit)?
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): ChildRenderingT {
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val childRendering = remember { mutableStateOf<ChildRenderingT?>(null) }
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// Since this function returns a value, it can't restart without also restarting its parent.
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// IsolateRecomposeScope allows the subtree to restart and only restarts us if the rendering value
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// actually changed.
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IsolateRecomposeScope(
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child = workflow,
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props = props,
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handler = handler,
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result = childRendering
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)
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@Suppress("UNCHECKED_CAST")
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return childRendering.value as ChildRenderingT
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}
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60+
@Composable
61+
private fun <PropsT, OutputT, RenderingT> IsolateRecomposeScope(
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child: ComposeWorkflow<PropsT, OutputT, RenderingT>,
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props: PropsT,
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handler: ((OutputT) -> Unit)?,
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result: MutableState<RenderingT>,
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) {
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result.value = child.Rendering(props, handler ?: {})
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}

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