Introduces BackStackScreen.name

`BackStackScreen` now implements `Compatible` and has a `name: String` field, just like `BodyAndOverlaysScreen`. This is in support of having multiple instances under a single `SavedStateRegistry` at a time. Our old trick of wrapping instances via `NamedScreen` doesn't work the the `BackStackScreen` creates the first classic `View` instance in Compose context, because the `NamedScreen` will be handled by Compose code. The old hack in `BackStackContainer` relies on `View.screen` holdling `NamedScreen(BackStackScreen)`, but in the Compose-eats-NamedScreen case it will just be `BackStackScreen`.

samples/containers/android/src/main/java/com/squareup/sample/container/overviewdetail/OverviewDetailContainer.kt

@@ -7,7 +7,6 @@ import com.squareup.sample.container.R
 import com.squareup.sample.container.overviewdetail.OverviewDetailConfig.Detail
 import com.squareup.sample.container.overviewdetail.OverviewDetailConfig.Overview
 import com.squareup.sample.container.overviewdetail.OverviewDetailConfig.Single
-import com.squareup.workflow1.ui.NamedScreen
 import com.squareup.workflow1.ui.ScreenViewFactory
 import com.squareup.workflow1.ui.ScreenViewRunner
 import com.squareup.workflow1.ui.ViewEnvironment
@@ -64,7 +63,7 @@ class OverviewDetailContainer(view: View) : ScreenViewRunner<OverviewDetailScree
 
       // Without this name, the two BackStackScreen containers will try
       // to sign up with SavedStateRegistry with the same id, and crash.
-      val overviewRendering = NamedScreen(rendering.overviewRendering, "Overview")
+      val overviewRendering = rendering.overviewRendering.withName("Overview")
       overviewStub!!.show(overviewRendering, overviewViewEnvironment)
 
       rendering.detailRendering

workflow-ui/core-android/src/main/java/com/squareup/workflow1/ui/androidx/WorkflowSavedStateRegistryAggregator.kt

@@ -162,7 +162,8 @@ public class WorkflowSavedStateRegistryAggregator {
         "Error registering SavedStateProvider: key \"$key\" is already in " +
           "use on parent SavedStateRegistryOwner $parentOwner. " +
           "This is most easily remedied by giving your container Screen rendering a unique " +
-          "Compatible.compatibilityKey, perhaps by wrapping it with Named.",
+          "Compatible.compatibilityKey -- note the name fields on BodyAndOverlaysScreen " +
+          "and BackStackScreen.",
         e
       )
     }

workflow-ui/core-common/api/core-common.api

@@ -209,14 +209,17 @@ public final class com/squareup/workflow1/ui/navigation/BackStackConfigKt {
 	public static final fun plus (Lcom/squareup/workflow1/ui/ViewEnvironment;Lcom/squareup/workflow1/ui/navigation/BackStackConfig;)Lcom/squareup/workflow1/ui/ViewEnvironment;
 }
 
-public final class com/squareup/workflow1/ui/navigation/BackStackScreen : com/squareup/workflow1/ui/Container, com/squareup/workflow1/ui/Screen {
+public final class com/squareup/workflow1/ui/navigation/BackStackScreen : com/squareup/workflow1/ui/Compatible, com/squareup/workflow1/ui/Container, com/squareup/workflow1/ui/Screen {
 	public static final field Companion Lcom/squareup/workflow1/ui/navigation/BackStackScreen$Companion;
 	public fun <init> (Lcom/squareup/workflow1/ui/Screen;[Lcom/squareup/workflow1/ui/Screen;)V
+	public fun <init> (Ljava/lang/String;Lcom/squareup/workflow1/ui/Screen;[Lcom/squareup/workflow1/ui/Screen;)V
 	public fun asSequence ()Lkotlin/sequences/Sequence;
 	public fun equals (Ljava/lang/Object;)Z
 	public final fun get (I)Lcom/squareup/workflow1/ui/Screen;
 	public final fun getBackStack ()Ljava/util/List;
+	public fun getCompatibilityKey ()Ljava/lang/String;
 	public final fun getFrames ()Ljava/util/List;
+	public final fun getName ()Ljava/lang/String;
 	public final fun getTop ()Lcom/squareup/workflow1/ui/Screen;
 	public fun hashCode ()I
 	public synthetic fun map (Lkotlin/jvm/functions/Function1;)Lcom/squareup/workflow1/ui/Container;
@@ -226,14 +229,18 @@ public final class com/squareup/workflow1/ui/navigation/BackStackScreen : com/sq
 }
 
 public final class com/squareup/workflow1/ui/navigation/BackStackScreen$Companion {
-	public final fun fromList (Ljava/util/List;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
-	public final fun fromListOrNull (Ljava/util/List;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public final fun fromList (Ljava/util/List;Ljava/lang/String;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public static synthetic fun fromList$default (Lcom/squareup/workflow1/ui/navigation/BackStackScreen$Companion;Ljava/util/List;Ljava/lang/String;ILjava/lang/Object;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public final fun fromListOrNull (Ljava/util/List;Ljava/lang/String;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public static synthetic fun fromListOrNull$default (Lcom/squareup/workflow1/ui/navigation/BackStackScreen$Companion;Ljava/util/List;Ljava/lang/String;ILjava/lang/Object;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
 }
 
 public final class com/squareup/workflow1/ui/navigation/BackStackScreenKt {
 	public static final fun plus (Lcom/squareup/workflow1/ui/navigation/BackStackScreen;Lcom/squareup/workflow1/ui/navigation/BackStackScreen;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
-	public static final fun toBackStackScreen (Ljava/util/List;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
-	public static final fun toBackStackScreenOrNull (Ljava/util/List;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public static final fun toBackStackScreen (Ljava/util/List;Ljava/lang/String;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public static synthetic fun toBackStackScreen$default (Ljava/util/List;Ljava/lang/String;ILjava/lang/Object;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public static final fun toBackStackScreenOrNull (Ljava/util/List;Ljava/lang/String;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
+	public static synthetic fun toBackStackScreenOrNull$default (Ljava/util/List;Ljava/lang/String;ILjava/lang/Object;)Lcom/squareup/workflow1/ui/navigation/BackStackScreen;
 }
 
 public final class com/squareup/workflow1/ui/navigation/BodyAndOverlaysScreen : com/squareup/workflow1/ui/Compatible, com/squareup/workflow1/ui/Screen {

workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/navigation/BackStackScreen.kt

@@ -1,5 +1,7 @@
 package com.squareup.workflow1.ui.navigation
 
+import com.squareup.workflow1.ui.Compatible
+import com.squareup.workflow1.ui.Compatible.Companion.keyFor
 import com.squareup.workflow1.ui.Container
 import com.squareup.workflow1.ui.Screen
 import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
@@ -18,18 +20,35 @@ import com.squareup.workflow1.ui.navigation.BackStackScreen.Companion.fromListOr
  *
  * @see fromList
  * @see fromListOrNull
+ *
+ * @param name included in the [compatibilityKey] of this screen, for ease
+ * of composition -- in classic Android views, view state persistence support
+ * requires peer BackStackScreens to have a unique keys.
  */
 @WorkflowUiExperimentalApi
 public class BackStackScreen<out StackedT : Screen> internal constructor(
-  public val frames: List<StackedT>
-) : Screen, Container<Screen, StackedT> {
+  public val frames: List<StackedT>,
+  public val name: String
+) : Screen, Container<Screen, StackedT>, Compatible {
+
   /**
-   * Creates a screen with elements listed from the [bottom] to the top.
+   * Creates a [BackStackScreen] with elements listed from the [bottom] to the top.
    */
   public constructor(
     bottom: StackedT,
     vararg rest: StackedT
-  ) : this(listOf(bottom) + rest)
+  ) : this(listOf(bottom) + rest, "")
+
+  /**
+   * Creates a [named][name] [BackStackScreen] with elements listed from the [bottom] to the top.
+   */
+  public constructor(
+    name: String,
+    bottom: StackedT,
+    vararg rest: StackedT
+  ) : this(listOf(bottom) + rest, name)
+
+  override val compatibilityKey: String = keyFor(this, name)
 
   override fun asSequence(): Sequence<StackedT> = frames.asSequence()
 
@@ -48,24 +67,34 @@ public class BackStackScreen<out StackedT : Screen> internal constructor(
   public override fun <StackedU : Screen> map(
     transform: (StackedT) -> StackedU
   ): BackStackScreen<StackedU> {
-    return frames.map(transform).toBackStackScreen()
+    return frames.map(transform).toBackStackScreen(name)
   }
 
   public fun <R : Screen> mapIndexed(transform: (index: Int, StackedT) -> R): BackStackScreen<R> {
     return frames.mapIndexed(transform)
-      .toBackStackScreen()
+      .toBackStackScreen(name)
   }
 
-  override fun equals(other: Any?): Boolean {
-    return (other as? BackStackScreen<*>)?.frames == frames
+  public fun withName(name: String): BackStackScreen<StackedT> = BackStackScreen(frames, name)
+
+  override fun toString(): String {
+    return name.takeIf { it.isNotEmpty() }?.let { "BackStackScreen-$it($frames)" }
+      ?: "BackStackScreen($frames)"
   }
 
-  override fun hashCode(): Int {
-    return frames.hashCode()
+  override fun equals(other: Any?): Boolean {
+    if (this === other) return true
+    if (javaClass != other?.javaClass) return false
+
+    other as BackStackScreen<*>
+
+    return (frames == other.frames && name == other.name)
   }
 
-  override fun toString(): String {
-    return "${this::class.java.simpleName}($frames)"
+  override fun hashCode(): Int {
+    var result = frames.hashCode()
+    result = 31 * result + name.hashCode()
+    return result
   }
 
   public companion object {
@@ -74,21 +103,27 @@ public class BackStackScreen<out StackedT : Screen> internal constructor(
      *
      * @throws IllegalArgumentException is [frames] is empty
      */
-    public fun <T : Screen> fromList(frames: List<T>): BackStackScreen<T> {
+    public fun <T : Screen> fromList(
+      frames: List<T>,
+      name: String = ""
+    ): BackStackScreen<T> {
       require(frames.isNotEmpty()) {
         "A BackStackScreen must have at least one frame."
       }
-      return BackStackScreen(frames)
+      return BackStackScreen(frames, name)
     }
 
     /**
      * Builds a [BackStackScreen] from a list of [frames], or returns `null`
      * if [frames] is empty.
      */
-    public fun <T : Screen> fromListOrNull(frames: List<T>): BackStackScreen<T>? {
+    public fun <T : Screen> fromListOrNull(
+      frames: List<T>,
+      name: String = ""
+    ): BackStackScreen<T>? {
       return when {
         frames.isEmpty() -> null
-        else -> BackStackScreen(frames)
+        else -> BackStackScreen(frames, name)
       }
     }
   }
@@ -103,13 +138,13 @@ public class BackStackScreen<out StackedT : Screen> internal constructor(
 public operator fun <T : Screen> BackStackScreen<T>.plus(
   other: BackStackScreen<T>?
 ): BackStackScreen<T> {
-  return other?.let { BackStackScreen(frames + it.frames) } ?: this
+  return other?.let { BackStackScreen(frames + it.frames, this.name) } ?: this
 }
 
 @WorkflowUiExperimentalApi
-public fun <T : Screen> List<T>.toBackStackScreenOrNull(): BackStackScreen<T>? =
-  fromListOrNull(this)
+public fun <T : Screen> List<T>.toBackStackScreenOrNull(name: String = ""): BackStackScreen<T>? =
+  fromListOrNull(this, name)
 
 @WorkflowUiExperimentalApi
-public fun <T : Screen> List<T>.toBackStackScreen(): BackStackScreen<T> =
-  Companion.fromList(this)
+public fun <T : Screen> List<T>.toBackStackScreen(name: String = ""): BackStackScreen<T> =
+  Companion.fromList(this, name)

workflow-ui/core-common/src/main/java/com/squareup/workflow1/ui/navigation/BodyAndOverlaysScreen.kt

@@ -69,8 +69,8 @@ import com.squareup.workflow1.ui.WorkflowUiExperimentalApi
  * a [BodyAndOverlaysScreen] rendering.
  *
  * @param name included in the [compatibilityKey] of this screen, for ease
- * of nesting -- on Android, view state persistence support requires each
- * BodyAndOverlaysScreen in a hierarchy to have a unique key
+ * of nesting -- in classic Android views, view state persistence support requires each
+ * BodyAndOverlaysScreen in a hierarchy to have a unique key.
  */
 @WorkflowUiExperimentalApi
 public class BodyAndOverlaysScreen<B : Screen, O : Overlay>(

workflow-ui/core-common/src/test/java/com/squareup/workflow1/ui/navigation/BackStackScreenTest.kt

@@ -33,23 +33,30 @@ internal class BackStackScreenTest {
   }
 
   @Test fun `plus another stack`() {
-    assertThat(
-      BackStackScreen(FooScreen(1), FooScreen(2), FooScreen(3)) + BackStackScreen(
+    val sum = BackStackScreen("fred", FooScreen(1), FooScreen(2), FooScreen(3)) +
+      BackStackScreen("barney", FooScreen(8), FooScreen(9), FooScreen(0))
+    assertThat(sum).isEqualTo(
+      BackStackScreen(
+        name = "fred",
+        FooScreen(1),
+        FooScreen(2),
+        FooScreen(3),
         FooScreen(8),
         FooScreen(9),
         FooScreen(0)
       )
     )
-      .isEqualTo(
-        BackStackScreen(
-          FooScreen(1),
-          FooScreen(2),
-          FooScreen(3),
-          FooScreen(8),
-          FooScreen(9),
-          FooScreen(0)
-        )
+    assertThat(sum).isNotEqualTo(
+      BackStackScreen(
+        name = "barney",
+        FooScreen(1),
+        FooScreen(2),
+        FooScreen(3),
+        FooScreen(8),
+        FooScreen(9),
+        FooScreen(0)
       )
+    )
   }
 
   @Test fun `unequal by order`() {
@@ -70,9 +77,10 @@ internal class BackStackScreenTest {
   @Test fun `bottom and rest`() {
     assertThat(
       BackStackScreen.fromList(
-        listOf(element = FooScreen(1)) + listOf(FooScreen(2), FooScreen(3), FooScreen(4))
+        listOf(element = FooScreen(1)) + listOf(FooScreen(2), FooScreen(3), FooScreen(4)),
+        "fred"
       )
-    ).isEqualTo(BackStackScreen(FooScreen(1), FooScreen(2), FooScreen(3), FooScreen(4)))
+    ).isEqualTo(BackStackScreen("fred", FooScreen(1), FooScreen(2), FooScreen(3), FooScreen(4)))
   }
 
   @Test fun singleton() {
@@ -84,18 +92,24 @@ internal class BackStackScreenTest {
 
   @Test fun map() {
     assertThat(
-      BackStackScreen(FooScreen(1), FooScreen(2), FooScreen(3)).map {
+      BackStackScreen("fred", FooScreen(1), FooScreen(2), FooScreen(3)).map {
         FooScreen(it.value * 2)
       }
     )
-      .isEqualTo(BackStackScreen(FooScreen(2), FooScreen(4), FooScreen(6)))
+      .isEqualTo(BackStackScreen("fred", FooScreen(2), FooScreen(4), FooScreen(6)))
   }
 
   @Test fun mapIndexed() {
-    val source = BackStackScreen(FooScreen("able"), FooScreen("baker"), FooScreen("charlie"))
+    val source =
+      BackStackScreen("fred", FooScreen("able"), FooScreen("baker"), FooScreen("charlie"))
     assertThat(source.mapIndexed { index, frame -> FooScreen("$index: ${frame.value}") })
       .isEqualTo(
-        BackStackScreen(FooScreen("0: able"), FooScreen("1: baker"), FooScreen("2: charlie"))
+        BackStackScreen(
+          "fred",
+          FooScreen("0: able"),
+          FooScreen("1: baker"),
+          FooScreen("2: charlie")
+        )
       )
   }
 
@@ -108,23 +122,28 @@ internal class BackStackScreenTest {
   }
 
   @Test fun fromList() {
-    assertThat(listOf(FooScreen(1), FooScreen(2), FooScreen(3)).toBackStackScreen())
-      .isEqualTo(BackStackScreen(FooScreen(1), FooScreen(2), FooScreen(3)))
+    assertThat(listOf(FooScreen(1), FooScreen(2), FooScreen(3)).toBackStackScreen("fred"))
+      .isEqualTo(BackStackScreen("fred", FooScreen(1), FooScreen(2), FooScreen(3)))
   }
 
   @Test fun fromListOrNull() {
-    assertThat(listOf(FooScreen(1), FooScreen(2), FooScreen(3)).toBackStackScreenOrNull())
-      .isEqualTo(BackStackScreen(FooScreen(1), FooScreen(2), FooScreen(3)))
+    assertThat(listOf(FooScreen(1), FooScreen(2), FooScreen(3)).toBackStackScreenOrNull("fred"))
+      .isEqualTo(BackStackScreen("fred", FooScreen(1), FooScreen(2), FooScreen(3)))
   }
 
   /**
    * To reminds us why we want the `out` in `BackStackScreen<out T : Screen>`.
    * Without this, using `BackStackScreen<*>` as `RenderingT` is not practical.
    */
-  @Test fun heterogenousPlusIsTolerable() {
+  @Test fun heterogeneousPlusIsTolerable() {
     val foo = BackStackScreen(FooScreen(1))
     val bar = BackStackScreen(BarScreen(1))
     val both = foo + bar
     assertThat(both).isEqualTo(foo + bar)
   }
+
+  @Test fun withName() {
+    assertThat(BackStackScreen("fred", FooScreen(1)).withName("barney"))
+      .isEqualTo(BackStackScreen("barney", FooScreen(1)))
+  }
 }