Create a widget protocol descriptor type

This has knowledge of the child IDs for this widget as well as the ability to create instances of it.

In the future this will also hold more information such as property IDs so that we can deserialize them on the Zipline thread.

redwood-protocol-host/src/commonMain/kotlin/app/cash/redwood/protocol/host/HostProtocolAdapter.kt

@@ -57,7 +57,7 @@ public class HostProtocolAdapter<W : Any>(
   private val leakDetector: LeakDetector,
 ) : ChangesSink {
   private val factory = when (factory) {
-    is GeneratedProtocolFactory -> factory
+    is GeneratedHostProtocol -> factory
   }
 
   private val nodes =
@@ -83,7 +83,8 @@ public class HostProtocolAdapter<W : Any>(
       val id = change.id
       when (change) {
         is Create -> {
-          val node = factory.createNode(id, change.tag) ?: continue
+          val widgetProtocol = factory.widget(change.tag) ?: continue
+          val node = widgetProtocol.createNode(id)
           val old = nodes.put(change.id.value, node)
           require(old == null) {
             "Insert attempted to replace existing widget with ID ${change.id.value}"

redwood-protocol-host/src/commonMain/kotlin/app/cash/redwood/protocol/host/NodeReuse.kt

@@ -31,15 +31,16 @@ import app.cash.redwood.protocol.host.HostProtocolAdapter.ReuseNode
  */
 @OptIn(RedwoodCodegenApi::class)
 internal fun shapesEqual(
-  factory: GeneratedProtocolFactory<*>,
+  factory: GeneratedHostProtocol<*>,
   a: ReuseNode<*>,
   b: ProtocolNode<*>,
 ): Boolean {
   if (!a.eligibleForReuse) return false // This node is ineligible.
   if (a.widgetTag == UnknownWidgetTag) return false // No 'Create' for this.
   if (b.widgetTag != a.widgetTag) return false // Widget types don't match.
 
-  val widgetChildren = factory.widgetChildren(a.widgetTag)
+  val widgetChildren = factory.widget(a.widgetTag)
+    ?.childrenTags
     ?: return true // Widget has no children.
 
   return widgetChildren.all { childrenTag ->
@@ -59,7 +60,7 @@ internal fun shapesEqual(
  */
 @OptIn(RedwoodCodegenApi::class)
 private fun childrenEqual(
-  factory: GeneratedProtocolFactory<*>,
+  factory: GeneratedHostProtocol<*>,
   aChildren: List<ReuseNode<*>>,
   bChildren: List<ProtocolNode<*>>,
   childrenTag: ChildrenTag,
@@ -81,15 +82,15 @@ private fun childrenEqual(
 /** Returns a hash of this node, or 0L if this node isn't eligible for reuse. */
 @OptIn(RedwoodCodegenApi::class)
 internal fun shapeHash(
-  factory: GeneratedProtocolFactory<*>,
+  factory: GeneratedHostProtocol<*>,
   node: ReuseNode<*>,
 ): Long {
   if (!node.eligibleForReuse) return 0L // This node is ineligible.
   if (node.widgetTag == UnknownWidgetTag) return 0L // No 'Create' for this.
 
   var result = node.widgetTag.value.toLong()
 
-  factory.widgetChildren(node.widgetTag)?.forEach { childrenTag ->
+  factory.widget(node.widgetTag)?.childrenTags?.forEach { childrenTag ->
     result = (result * 37L) + childrenTag
     var childCount = 0
     for (child in node.children) {
@@ -106,11 +107,11 @@ internal fun shapeHash(
 /** Returns the same hash as [shapeHash], but on an already-built [ProtocolNode]. */
 @OptIn(RedwoodCodegenApi::class)
 internal fun shapeHash(
-  factory: GeneratedProtocolFactory<*>,
+  factory: GeneratedHostProtocol<*>,
   node: ProtocolNode<*>,
 ): Long {
   var result = node.widgetTag.value.toLong()
-  factory.widgetChildren(node.widgetTag)?.forEach { childrenTag ->
+  factory.widget(node.widgetTag)?.childrenTags?.forEach { childrenTag ->
     result = (result * 37L) + childrenTag
     val children = node.children(ChildrenTag(childrenTag))
       ?: return@forEach // This acts like a 'continue'.

redwood-protocol-host/src/commonMain/kotlin/app/cash/redwood/protocol/host/ProtocolFactory.kt

@@ -35,20 +35,20 @@ public sealed interface ProtocolFactory<W : Any> {
 }
 
 /**
- * [ProtocolFactory] but containing codegen APIs.
+ * [ProtocolFactory] but containing codegen APIs for a schema.
  *
  * @suppress
  */
 @RedwoodCodegenApi
-public interface GeneratedProtocolFactory<W : Any> : ProtocolFactory<W> {
+public interface GeneratedHostProtocol<W : Any> : ProtocolFactory<W> {
   /**
-   * Create a new protocol node with [id] of the specified [tag].
+   * Look up host protocol information for a widget with the given [tag].
    *
    * Invalid [tag] values can either produce an exception or result in `null` being returned.
    * If `null` is returned, the caller should make every effort to ignore this node and
    * continue executing.
    */
-  public fun createNode(id: Id, tag: WidgetTag): ProtocolNode<W>?
+  public fun widget(tag: WidgetTag): WidgetHostProtocol<W>?
 
   /**
    * Create a new modifier from the specified [element].
@@ -57,12 +57,22 @@ public interface GeneratedProtocolFactory<W : Any> : ProtocolFactory<W> {
    * or result in the unit [`Modifier`][Modifier.Companion] being returned.
    */
   public fun createModifier(element: ModifierElement): Modifier
+}
+
+/**
+ * Protocol APIs for a widget definition.
+ *
+ * @suppress
+ */
+@RedwoodCodegenApi
+public interface WidgetHostProtocol<W : Any> {
+  /** Create an instance of this widget wrapped as a [ProtocolNode] with the given [id]. */
+  public fun createNode(id: Id): ProtocolNode<W>
 
   /**
-   * Look up known children tags for the given widget [tag]. These are stored as a bare [IntArray]
-   * for efficiency, but are otherwise an array of [ChildrenTag] instances.
-   *
-   * @return `null` when widget has no children
+   * Look up known children tags for this widget. These are stored as a bare [IntArray]
+   * for efficiency, but are otherwise an array of [ChildrenTag] instances. A value of
+   * `null` indicates no children.
    */
-  public fun widgetChildren(tag: WidgetTag): IntArray?
+  public val childrenTags: IntArray?
 }

redwood-protocol-host/src/commonTest/kotlin/app/cash/redwood/protocol/host/ProtocolFactoryTest.kt

@@ -60,7 +60,7 @@ class ProtocolFactoryTest {
     )
 
     val t = assertFailsWith<IllegalArgumentException> {
-      factory.createNode(Id(1), WidgetTag(345432))
+      factory.widget(WidgetTag(345432))
     }
     assertThat(t).hasMessage("Unknown widget tag 345432")
   }
@@ -76,8 +76,7 @@ class ProtocolFactoryTest {
       mismatchHandler = handler,
     )
 
-    assertThat(factory.createNode(Id(1), WidgetTag(345432))).isNull()
-
+    assertThat(factory.widget(WidgetTag(345432))).isNull()
     assertThat(handler.events.single()).isEqualTo("Unknown widget 345432")
   }
 
@@ -216,7 +215,7 @@ class ProtocolFactoryTest {
         RedwoodLazyLayout = RedwoodLazyLayoutTestingWidgetFactory(),
       ),
     )
-    val button = factory.createNode(Id(1), WidgetTag(4))!!
+    val button = factory.widget(WidgetTag(4))!!.createNode(Id(1))
 
     val t = assertFailsWith<IllegalArgumentException> {
       button.children(ChildrenTag(345432))
@@ -235,7 +234,7 @@ class ProtocolFactoryTest {
       mismatchHandler = handler,
     )
 
-    val button = factory.createNode(Id(1), WidgetTag(4))!!
+    val button = factory.widget(WidgetTag(4))!!.createNode(Id(1))
     assertThat(button.children(ChildrenTag(345432))).isNull()
 
     assertThat(handler.events.single()).isEqualTo("Unknown children 345432 for 4")
@@ -255,7 +254,7 @@ class ProtocolFactoryTest {
       ),
       json = json,
     )
-    val textInput = factory.createNode(Id(1), WidgetTag(5))!!
+    val textInput = factory.widget(WidgetTag(5))!!.createNode(Id(1))
 
     val throwingEventSink = UiEventSink { error(it) }
     textInput.apply(PropertyChange(Id(1), PropertyTag(2), JsonPrimitive("PT10S")), throwingEventSink)
@@ -271,7 +270,7 @@ class ProtocolFactoryTest {
         RedwoodLazyLayout = RedwoodLazyLayoutTestingWidgetFactory(),
       ),
     )
-    val button = factory.createNode(Id(1), WidgetTag(4))!!
+    val button = factory.widget(WidgetTag(4))!!.createNode(Id(1))
 
     val change = PropertyChange(Id(1), PropertyTag(345432))
     val eventSink = UiEventSink { throw UnsupportedOperationException() }
@@ -291,7 +290,7 @@ class ProtocolFactoryTest {
       ),
       mismatchHandler = handler,
     )
-    val button = factory.createNode(Id(1), WidgetTag(4))!!
+    val button = factory.widget(WidgetTag(4))!!.createNode(Id(1))
 
     button.apply(PropertyChange(Id(1), PropertyTag(345432))) { throw UnsupportedOperationException() }
 
@@ -312,7 +311,7 @@ class ProtocolFactoryTest {
       ),
       json = json,
     )
-    val textInput = factory.createNode(Id(1), WidgetTag(5))!!
+    val textInput = factory.widget(WidgetTag(5))!!.createNode(Id(1))
 
     val eventSink = RecordingUiEventSink()
     textInput.apply(PropertyChange(Id(1), PropertyTag(4), JsonPrimitive(true)), eventSink)