BREAKING: Replaces ComposeScreenViewFactory with ScreenComposableFactory

This commit takes advantage of the new `ViewRegistry.Key` (which allows renderings to be bound to multiple UI factories) to fix a long standing problem where wrapper screens -- things like `NamedScreen` and `EnvironmentScreen` -- used in a Compose context would cause needless calls to `@Composeable fun AndroidView()` and `ComposeView()`.

For example, consider this rendering:

```
BodyAndOverlaysScreen(
  body = SomeComposeScreen(
    EnvironmentScreen(
      SomeOtherComposeScreen
    )
  )
)
```

Before this change, that would create a View hierarchy something like this:

```
BodyAndOverlaysContainer : FrameLayout {
  mChildren[0] = ComposeView {
    // compose land
    SomeComposeScreen.Content {
      AndroidView {
        ComposeView {
          // nested compose land
            SomeOtherComposeScreen.Content()
```

Now it will look this way:

```
BodyAndOverlaysContainer : FrameLayout {
  mChildren[0] = ComposeView {
    // compose land
    SomeComposeScreen.Content {
      SomeOtherComposeScreen.Content()
```

`ScreenComposableFactory` replaces `ComposeScreenViewFactory`, and `ComposeScreen` no longer extends `AndroidScreen`. Compose support is now a first class citizen, instead of a hack bolted on to View support.

Unfortunately, `ViewEnvironment.withComposeInteropSupport()` (see below) now must be called near the root of a Workflow app to enable the seamless Compose > Classic > Compose handling that used to be built in to `WorkflowRendering` and `ComposeScreenViewFactory`. This means that call is required for Compose support for built in rendering types like `BodyAndOverlaysScreen` and `BackStackScreen`, which so far are backed only by classic View implementations.

Other introductions, changes:

- `Screen.toComposableFactory()`, used by `WorkflowRendering()` in the same way that `WorkflowViewStub` uses `Screen.toViewFactory()`

- `ScreenComposableFactoryFinder`, a `ViewEnvironment`-based strategy object used by `Screen.toComposableFactory()` the same way that `Screen.toViewFactory()` uses `ScreenViewFactoryFinder`. The default implementation provides Compose bindings for `NamedScreen` and `EnvironmentScreen`, fixing #546.

- `ScreenViewFactoryFinder.getViewFactoryForRendering()` can now return `null`. A `requireViewFactoryForRendering()` extension is introduced for use when `null` is not acceptable.

- `ViewEnvironment.withComposeInteropSupport()`, which wraps the found `ScreenComposableFactoryFinder` and `ScreenViewFactoryFinder` with implementations that allow Compose contexts to handle renderings bound only to `ScreenViewFactory`, and classic contexts to handle renderings bound only to `ScreenComposableFactory`. Replaces the logic that used to be in the private `ScreenViewFactory.asComposeViewFactory()` extension in `WorkflowRendering()`.

- `Screen.Preview()` is introduced. The existing `Preview()` extension functions were tied to `ScreenViewFactory`, making them much less useful. It is still the case that previews work for non-Compose UI code just fine. Which is pretty cool, really.

Fixes #546

Author: rjrjr

samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocompose/App.kt

@@ -14,17 +14,16 @@ import androidx.compose.ui.unit.dp
 import com.squareup.workflow1.WorkflowExperimentalRuntime
 import com.squareup.workflow1.config.AndroidRuntimeConfigTools
 import com.squareup.workflow1.ui.ViewEnvironment
-import com.squareup.workflow1.ui.ViewRegistry
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
 import com.squareup.workflow1.ui.compose.WorkflowRendering
 import com.squareup.workflow1.ui.compose.renderAsState
-import com.squareup.workflow1.ui.plus
+import com.squareup.workflow1.ui.compose.withComposeInteropSupport
 
-private val viewEnvironment = ViewEnvironment.EMPTY + ViewRegistry(HelloBinding)
+private val viewEnvironment = ViewEnvironment.EMPTY.withComposeInteropSupport()
 
 @Composable fun App() {
   MaterialTheme {
-    val rendering by HelloWorkflow.renderAsState(
+    val rendering by HelloComposeWorkflow.renderAsState(
       props = Unit,
       runtimeConfig = AndroidRuntimeConfigTools.getAppWorkflowRuntimeConfig(),
       onOutput = {}

samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocompose/HelloBinding.kt

@@ -0,0 +1,40 @@
+package com.squareup.sample.compose.hellocompose
+
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.wrapContentSize
+import androidx.compose.material.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.tooling.preview.Preview
+import com.squareup.workflow1.ui.ViewEnvironment
+import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
+import com.squareup.workflow1.ui.compose.ComposeScreen
+import com.squareup.workflow1.ui.compose.tooling.Preview
+
+@OptIn(WorkflowUiExperimentalApi::class)
+data class HelloComposeScreen(
+  val message: String,
+  val onClick: () -> Unit
+) : ComposeScreen {
+  @Composable override fun Content(viewEnvironment: ViewEnvironment) {
+    Text(
+      message,
+      modifier = Modifier
+        .clickable(onClick = onClick)
+        .fillMaxSize()
+        .wrapContentSize(Alignment.Center)
+    )
+  }
+}
+
+@OptIn(WorkflowUiExperimentalApi::class)
+@Preview(heightDp = 150, showBackground = true)
+@Composable
+private fun HelloPreview() {
+  HelloComposeScreen(
+    "Hello!",
+    onClick = {}
+  ).Preview()
+}

samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocompose/HelloComposeScreen.kt

@@ -1,17 +1,14 @@
 package com.squareup.sample.compose.hellocompose
 
-import com.squareup.sample.compose.hellocompose.HelloWorkflow.Rendering
-import com.squareup.sample.compose.hellocompose.HelloWorkflow.State
-import com.squareup.sample.compose.hellocompose.HelloWorkflow.State.Goodbye
-import com.squareup.sample.compose.hellocompose.HelloWorkflow.State.Hello
+import com.squareup.sample.compose.hellocompose.HelloComposeWorkflow.State
+import com.squareup.sample.compose.hellocompose.HelloComposeWorkflow.State.Goodbye
+import com.squareup.sample.compose.hellocompose.HelloComposeWorkflow.State.Hello
 import com.squareup.workflow1.Snapshot
 import com.squareup.workflow1.StatefulWorkflow
 import com.squareup.workflow1.action
 import com.squareup.workflow1.parse
-import com.squareup.workflow1.ui.Screen
-import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
 
-object HelloWorkflow : StatefulWorkflow<Unit, State, Nothing, Rendering>() {
+object HelloComposeWorkflow : StatefulWorkflow<Unit, State, Nothing, HelloComposeScreen>() {
   enum class State {
     Hello,
     Goodbye;
@@ -22,12 +19,6 @@ object HelloWorkflow : StatefulWorkflow<Unit, State, Nothing, Rendering>() {
     }
   }
 
-  @OptIn(WorkflowUiExperimentalApi::class)
-  data class Rendering(
-    val message: String,
-    val onClick: () -> Unit
-  ) : Screen
-
   private val helloAction = action {
     state = state.theOtherState()
   }
@@ -42,7 +33,7 @@ object HelloWorkflow : StatefulWorkflow<Unit, State, Nothing, Rendering>() {
     renderProps: Unit,
     renderState: State,
     context: RenderContext
-  ): Rendering = Rendering(
+  ): HelloComposeScreen = HelloComposeScreen(
     message = renderState.name,
     onClick = { context.actionSink.send(helloAction) }
   )

samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocompose/HelloWorkflow.kt renamed to samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocompose/HelloComposeWorkflow.kt

@@ -9,11 +9,11 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.tooling.preview.Preview
 import com.squareup.sample.compose.hellocomposebinding.HelloWorkflow.Rendering
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
-import com.squareup.workflow1.ui.compose.composeScreenViewFactory
+import com.squareup.workflow1.ui.compose.ScreenComposableFactory
 import com.squareup.workflow1.ui.compose.tooling.Preview
 
 @OptIn(WorkflowUiExperimentalApi::class)
-val HelloBinding = composeScreenViewFactory<Rendering> { rendering, _ ->
+val HelloBinding = ScreenComposableFactory<Rendering> { rendering, _ ->
   Text(
     rendering.message,
     modifier = Modifier

samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocomposebinding/HelloBinding.kt

@@ -17,6 +17,7 @@ import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.ViewRegistry
 import com.squareup.workflow1.ui.WorkflowLayout
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
+import com.squareup.workflow1.ui.compose.withComposeInteropSupport
 import com.squareup.workflow1.ui.compose.withCompositionRoot
 import com.squareup.workflow1.ui.plus
 import com.squareup.workflow1.ui.renderWorkflowIn
@@ -25,13 +26,15 @@ import kotlinx.coroutines.flow.StateFlow
 
 @OptIn(WorkflowUiExperimentalApi::class)
 private val viewEnvironment =
-  (ViewEnvironment.EMPTY + ViewRegistry(HelloBinding)).withCompositionRoot { content ->
-    MaterialTheme(content = content)
-  }
+  (ViewEnvironment.EMPTY + ViewRegistry(HelloBinding))
+    .withCompositionRoot { content ->
+      MaterialTheme(content = content)
+    }
+    .withComposeInteropSupport()
 
 /**
  * Demonstrates how to create and display a view factory with
- * [composeScreenViewFactory][com.squareup.workflow1.ui.compose.composeScreenViewFactory].
+ * [screenComposableFactory][com.squareup.workflow1.ui.compose.ScreenComposableFactory].
  */
 class HelloBindingActivity : AppCompatActivity() {
   @OptIn(WorkflowUiExperimentalApi::class)

samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocomposebinding/HelloBindingActivity.kt

@@ -10,10 +10,14 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.squareup.workflow1.WorkflowExperimentalRuntime
 import com.squareup.workflow1.config.AndroidRuntimeConfigTools
+import com.squareup.workflow1.mapRendering
 import com.squareup.workflow1.ui.Screen
+import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.WorkflowLayout
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
+import com.squareup.workflow1.ui.compose.withComposeInteropSupport
 import com.squareup.workflow1.ui.renderWorkflowIn
+import com.squareup.workflow1.ui.withEnvironment
 import kotlinx.coroutines.flow.StateFlow
 
 class HelloComposeWorkflowActivity : AppCompatActivity() {
@@ -30,7 +34,9 @@ class HelloComposeWorkflowActivity : AppCompatActivity() {
     @OptIn(WorkflowUiExperimentalApi::class)
     val renderings: StateFlow<Screen> by lazy {
       renderWorkflowIn(
-        workflow = HelloWorkflow,
+        workflow = HelloWorkflow.mapRendering {
+          it.withEnvironment(ViewEnvironment.EMPTY.withComposeInteropSupport())
+        },
         scope = viewModelScope,
         savedStateHandle = savedState,
         runtimeConfig = AndroidRuntimeConfigTools.getAppWorkflowRuntimeConfig()

samples/compose-samples/src/main/java/com/squareup/sample/compose/hellocomposeworkflow/HelloComposeWorkflowActivity.kt

@@ -10,10 +10,14 @@ import androidx.lifecycle.ViewModel
 import androidx.lifecycle.viewModelScope
 import com.squareup.workflow1.WorkflowExperimentalRuntime
 import com.squareup.workflow1.config.AndroidRuntimeConfigTools
+import com.squareup.workflow1.mapRendering
 import com.squareup.workflow1.ui.Screen
+import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.WorkflowLayout
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
+import com.squareup.workflow1.ui.compose.withComposeInteropSupport
 import com.squareup.workflow1.ui.renderWorkflowIn
+import com.squareup.workflow1.ui.withEnvironment
 import kotlinx.coroutines.flow.StateFlow
 
 /**
@@ -34,7 +38,9 @@ class InlineRenderingActivity : AppCompatActivity() {
     @OptIn(WorkflowUiExperimentalApi::class)
     val renderings: StateFlow<Screen> by lazy {
       renderWorkflowIn(
-        workflow = InlineRenderingWorkflow,
+        workflow = InlineRenderingWorkflow.mapRendering {
+          it.withEnvironment(ViewEnvironment.EMPTY.withComposeInteropSupport())
+        },
         scope = viewModelScope,
         savedStateHandle = savedState,
         runtimeConfig = AndroidRuntimeConfigTools.getAppWorkflowRuntimeConfig()

samples/compose-samples/src/main/java/com/squareup/sample/compose/inlinerendering/InlineRenderingActivity.kt

@@ -21,14 +21,14 @@ import com.squareup.workflow1.StatefulWorkflow
 import com.squareup.workflow1.WorkflowExperimentalRuntime
 import com.squareup.workflow1.config.AndroidRuntimeConfigTools
 import com.squareup.workflow1.parse
-import com.squareup.workflow1.ui.AndroidScreen
+import com.squareup.workflow1.ui.Screen
 import com.squareup.workflow1.ui.ViewEnvironment
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
 import com.squareup.workflow1.ui.compose.ComposeScreen
 import com.squareup.workflow1.ui.compose.WorkflowRendering
 import com.squareup.workflow1.ui.compose.renderAsState
 
-object InlineRenderingWorkflow : StatefulWorkflow<Unit, Int, Nothing, AndroidScreen<*>>() {
+object InlineRenderingWorkflow : StatefulWorkflow<Unit, Int, Nothing, Screen>() {
 
   override fun initialState(
     props: Unit,
@@ -39,7 +39,7 @@ object InlineRenderingWorkflow : StatefulWorkflow<Unit, Int, Nothing, AndroidScr
     renderProps: Unit,
     renderState: Int,
     context: RenderContext
-  ): AndroidScreen<*> = ComposeScreen {
+  ) = ComposeScreen {
     Box {
       Button(onClick = context.eventHandler { state += 1 }) {
         Text("Counter: ")

samples/compose-samples/src/main/java/com/squareup/sample/compose/inlinerendering/InlineRenderingWorkflow.kt

@@ -37,7 +37,7 @@ val samples = listOf(
   Sample(
     "Hello Compose Binding",
     HelloBindingActivity::class,
-    "Creates a ViewFactory using composeViewFactory."
+    "Binds a Screen to a UI factory using ScreenComposableFactory()."
   ) { DrawHelloRenderingPreview() },
   Sample(
     "Nested Renderings",