Implement host-side protocol widget reuse

This does not yet support sending the detach flag from the guest.

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

@@ -36,7 +36,6 @@ import app.cash.redwood.protocol.RedwoodVersion
 import app.cash.redwood.protocol.WidgetTag
 import app.cash.redwood.widget.ChangeListener
 import app.cash.redwood.widget.Widget
-import kotlin.collections.mutableMapOf
 import kotlin.native.ObjCName
 
 /**
@@ -107,10 +106,12 @@ public class HostProtocolAdapter<W : Any>(
             }
 
             is Remove -> {
-              for (childIndex in change.index until change.index + change.count) {
-                val child = children.nodes[childIndex]
-                child.visitIds(removeNodeById)
-                poolOrDetach(child)
+              if (!change.detach) {
+                for (childIndex in change.index until change.index + change.count) {
+                  val child = children.nodes[childIndex]
+                  child.visitIds(removeNodeById)
+                  poolOrDetach(child)
+                }
               }
               children.remove(change.index, change.count)
             }

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

@@ -29,6 +29,7 @@ import app.cash.redwood.protocol.PropertyChange
 import app.cash.redwood.protocol.PropertyTag
 import app.cash.redwood.protocol.WidgetTag
 import app.cash.redwood.protocol.guest.guestRedwoodVersion
+import app.cash.redwood.testing.WidgetValue
 import app.cash.redwood.widget.MutableListChildren
 import assertk.assertFailure
 import assertk.assertThat
@@ -37,7 +38,9 @@ import assertk.assertions.isEqualTo
 import assertk.assertions.isInstanceOf
 import assertk.assertions.message
 import com.example.redwood.testapp.protocol.host.TestSchemaProtocolFactory
+import com.example.redwood.testapp.testing.TestRowValue
 import com.example.redwood.testapp.testing.TestSchemaTestingWidgetFactory
+import com.example.redwood.testapp.testing.TextValue
 import com.example.redwood.testapp.widget.TestSchemaWidgetSystem
 import kotlin.test.Test
 import kotlin.test.assertFailsWith
@@ -204,9 +207,10 @@ class HostProtocolAdapterTest {
   }
 
   @Test fun entireSubtreeRemoved() {
+    val container = MutableListChildren<WidgetValue>()
     val host = HostProtocolAdapter(
       guestVersion = guestRedwoodVersion,
-      container = MutableListChildren(),
+      container = container,
       factory = TestSchemaProtocolFactory(
         widgetSystem = TestSchemaWidgetSystem(
           TestSchema = TestSchemaTestingWidgetFactory(),
@@ -263,4 +267,69 @@ class HostProtocolAdapterTest {
       .message()
       .isEqualTo("Unknown widget ID 3")
   }
+
+  @Test fun detachAndAdd() {
+    val container = MutableListChildren<WidgetValue>()
+    val host = HostProtocolAdapter(
+      guestVersion = guestRedwoodVersion,
+      container = container,
+      factory = TestSchemaProtocolFactory(
+        widgetSystem = TestSchemaWidgetSystem(
+          TestSchema = TestSchemaTestingWidgetFactory(),
+          RedwoodLayout = RedwoodLayoutTestingWidgetFactory(),
+          RedwoodLazyLayout = RedwoodLazyLayoutTestingWidgetFactory(),
+        ),
+      ),
+      eventSink = ::error,
+      leakDetector = LeakDetector.none(),
+    )
+
+    // TestRow {
+    //   TestRow {
+    //     Text("hello")
+    host.sendChanges(
+      listOf(
+        // TestRow
+        Create(Id(1), WidgetTag(1)),
+        ModifierChange(Id(1)),
+        // TestRow
+        Create(Id(2), WidgetTag(1)),
+        ModifierChange(Id(2)),
+        // Text
+        Create(Id(3), WidgetTag(3)),
+        PropertyChange(Id(3), WidgetTag(3), PropertyTag(1), JsonPrimitive("hello")),
+        ModifierChange(Id(3)),
+        Add(Id(2), ChildrenTag(1), Id(3), 0),
+        Add(Id(1), ChildrenTag(1), Id(2), 0),
+        Add(Id.Root, ChildrenTag.Root, Id(1), 0),
+      ),
+    )
+
+    host.sendChanges(
+      listOf(
+        // Detach inner TestRow.
+        Remove(Id(1), ChildrenTag(1), 0, 1, detach = true),
+        // Remove outer TestRow.
+        Remove(Id.Root, ChildrenTag.Root, 0, 1),
+        // New outer TestRow.
+        Create(Id(4), WidgetTag(1)),
+        ModifierChange(Id(4)),
+        Add(Id.Root, ChildrenTag.Root, Id(4), 0),
+        // Re-attach inner TestRow.
+        Add(Id(4), ChildrenTag(1), Id(2), 0),
+      ),
+    )
+
+    assertThat(container.single().value).isEqualTo(
+      TestRowValue(
+        children = listOf(
+          TestRowValue(
+            children = listOf(
+              TextValue(text = "hello"),
+            ),
+          ),
+        ),
+      ),
+    )
+  }
 }

redwood-protocol/api/redwood-protocol.api

@@ -79,9 +79,10 @@ public final class app/cash/redwood/protocol/ChildrenChange$Move$Companion {
 
 public final class app/cash/redwood/protocol/ChildrenChange$Remove : app/cash/redwood/protocol/ChildrenChange {
 	public static final field Companion Lapp/cash/redwood/protocol/ChildrenChange$Remove$Companion;
-	public synthetic fun <init> (IIIILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (IIIIZLkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public fun equals (Ljava/lang/Object;)Z
 	public final fun getCount ()I
+	public final fun getDetach ()Z
 	public fun getId-0HhLjSo ()I
 	public final fun getIndex ()I
 	public fun getTag-b0W0yNk ()I
@@ -101,7 +102,8 @@ public synthetic class app/cash/redwood/protocol/ChildrenChange$Remove$$serializ
 }
 
 public final class app/cash/redwood/protocol/ChildrenChange$Remove$Companion {
-	public final fun invoke-ARs5Qwk (IIII)Lapp/cash/redwood/protocol/ChildrenChange$Remove;
+	public final fun invoke-HpxY78w (IIIIZ)Lapp/cash/redwood/protocol/ChildrenChange$Remove;
+	public static synthetic fun invoke-HpxY78w$default (Lapp/cash/redwood/protocol/ChildrenChange$Remove$Companion;IIIIZILjava/lang/Object;)Lapp/cash/redwood/protocol/ChildrenChange$Remove;
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
 

redwood-protocol/api/redwood-protocol.klib.api

@@ -91,6 +91,8 @@ sealed interface app.cash.redwood.protocol/ChildrenChange : app.cash.redwood.pro
     final class Remove : app.cash.redwood.protocol/ChildrenChange { // app.cash.redwood.protocol/ChildrenChange.Remove|null[0]
         final val count // app.cash.redwood.protocol/ChildrenChange.Remove.count|{}count[0]
             final fun <get-count>(): kotlin/Int // app.cash.redwood.protocol/ChildrenChange.Remove.count.<get-count>|<get-count>(){}[0]
+        final val detach // app.cash.redwood.protocol/ChildrenChange.Remove.detach|{}detach[0]
+            final fun <get-detach>(): kotlin/Boolean // app.cash.redwood.protocol/ChildrenChange.Remove.detach.<get-detach>|<get-detach>(){}[0]
         final val id // app.cash.redwood.protocol/ChildrenChange.Remove.id|{}id[0]
             final fun <get-id>(): app.cash.redwood.protocol/Id // app.cash.redwood.protocol/ChildrenChange.Remove.id.<get-id>|<get-id>(){}[0]
         final val index // app.cash.redwood.protocol/ChildrenChange.Remove.index|{}index[0]
@@ -112,7 +114,7 @@ sealed interface app.cash.redwood.protocol/ChildrenChange : app.cash.redwood.pro
         }
 
         final object Companion { // app.cash.redwood.protocol/ChildrenChange.Remove.Companion|null[0]
-            final fun invoke(app.cash.redwood.protocol/Id, app.cash.redwood.protocol/ChildrenTag, kotlin/Int, kotlin/Int): app.cash.redwood.protocol/ChildrenChange.Remove // app.cash.redwood.protocol/ChildrenChange.Remove.Companion.invoke|invoke(app.cash.redwood.protocol.Id;app.cash.redwood.protocol.ChildrenTag;kotlin.Int;kotlin.Int){}[0]
+            final fun invoke(app.cash.redwood.protocol/Id, app.cash.redwood.protocol/ChildrenTag, kotlin/Int, kotlin/Int, kotlin/Boolean = ...): app.cash.redwood.protocol/ChildrenChange.Remove // app.cash.redwood.protocol/ChildrenChange.Remove.Companion.invoke|invoke(app.cash.redwood.protocol.Id;app.cash.redwood.protocol.ChildrenTag;kotlin.Int;kotlin.Int;kotlin.Boolean){}[0]
             final fun serializer(): kotlinx.serialization/KSerializer<app.cash.redwood.protocol/ChildrenChange.Remove> // app.cash.redwood.protocol/ChildrenChange.Remove.Companion.serializer|serializer(){}[0]
         }
     }

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

@@ -248,6 +248,12 @@ public sealed interface ChildrenChange : Change {
     private val _tag: Int,
     public val index: Int,
     public val count: Int,
+    /**
+     * When true, the associated nodes should only be detached from the tree with the expectation
+     * that a future [Add] will re-attach them. Otherwise, nodes should be detached and fully
+     * removed for garbage collection.
+     */
+    public val detach: Boolean = false,
   ) : ChildrenChange {
     override val id: Id get() = Id(_id)
     override val tag: ChildrenTag get() = ChildrenTag(_tag)
@@ -258,7 +264,8 @@ public sealed interface ChildrenChange : Change {
         tag: ChildrenTag,
         index: Int,
         count: Int,
-      ): Remove = Remove(id.value, tag.value, index, count)
+        detach: Boolean = false,
+      ): Remove = Remove(id.value, tag.value, index, count, detach)
     }
   }
 }

redwood-protocol/src/commonTest/kotlin/app/cash/redwood/protocol/SnapshotChangeListTest.kt

@@ -71,7 +71,7 @@ class SnapshotChangeListTest {
       |
       |Found:
       | - Move(_id=0, _tag=1, fromIndex=1, toIndex=2, count=3)
-      | - Remove(_id=0, _tag=1, index=1, count=2)
+      | - Remove(_id=0, _tag=1, index=1, count=2, detach=false)
       """.trimMargin(),
     )
   }