Defer serializing event args to JSON

Until we're on the Zipline thread instead of the UI thread.

CHANGELOG.md

@@ -7,7 +7,7 @@ New:
 - Source-based schema parser is now the default. Can be disabled in your schema module with `redwood { useFir = false }`.
 
 Changed:
-- Nothing yet!
+- In Treehouse, events from the UI are now serialized on a background thread. This means that there is both a delay and a thread change between when a UI binding sends an event and when that object is converted to JSON. All arguments to events must not be mutable and support property reads on any thread. Best practice is for all event arguments to be completely immutable.
 
 Fixed:
 - Nothing yet!

redwood-protocol-host/build.gradle

@@ -6,6 +6,7 @@ redwoodBuild {
 }
 
 apply plugin: 'com.github.gmazzo.buildconfig'
+apply plugin: 'dev.drewhamilton.poko'
 
 kotlin {
   sourceSets {

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

@@ -25,7 +25,6 @@ import app.cash.redwood.protocol.ChildrenChange.Move
 import app.cash.redwood.protocol.ChildrenChange.Remove
 import app.cash.redwood.protocol.ChildrenTag
 import app.cash.redwood.protocol.Create
-import app.cash.redwood.protocol.EventSink
 import app.cash.redwood.protocol.Id
 import app.cash.redwood.protocol.ModifierChange
 import app.cash.redwood.protocol.PropertyChange
@@ -50,7 +49,7 @@ public class HostProtocolAdapter<W : Any>(
   guestVersion: RedwoodVersion,
   container: Widget.Children<W>,
   factory: ProtocolFactory<W>,
-  private val eventSink: EventSink,
+  private val eventSink: UiEventSink,
 ) : ChangesSink {
   private val factory = requireNotNull(factory as? GeneratedProtocolFactory<W>) {
     "Factory ${factory::class} was not generated by Redwood or is out of date"
@@ -378,7 +377,7 @@ private class RootProtocolNode<W : Any>(
   Widget<W> {
   private val children = ProtocolChildren(children)
 
-  override fun apply(change: PropertyChange, eventSink: EventSink) {
+  override fun apply(change: PropertyChange, eventSink: UiEventSink) {
     throw AssertionError("unexpected: $change")
   }
 

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

@@ -18,7 +18,6 @@ package app.cash.redwood.protocol.host
 import app.cash.redwood.Modifier
 import app.cash.redwood.RedwoodCodegenApi
 import app.cash.redwood.protocol.ChildrenTag
-import app.cash.redwood.protocol.EventSink
 import app.cash.redwood.protocol.Id
 import app.cash.redwood.protocol.PropertyChange
 import app.cash.redwood.protocol.WidgetTag
@@ -48,7 +47,7 @@ public abstract class ProtocolNode<W : Any>(
   /** Assigned when the node is added to the pool. */
   internal var shapeHash = 0L
 
-  public abstract fun apply(change: PropertyChange, eventSink: EventSink)
+  public abstract fun apply(change: PropertyChange, eventSink: UiEventSink)
 
   public fun updateModifier(modifier: Modifier) {
     widget.modifier = modifier

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

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2024 Square, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package app.cash.redwood.protocol.host
+
+import app.cash.redwood.protocol.Event
+import app.cash.redwood.protocol.EventSink
+import app.cash.redwood.protocol.EventTag
+import app.cash.redwood.protocol.Id
+import dev.drewhamilton.poko.Poko
+import kotlinx.serialization.SerializationStrategy
+import kotlinx.serialization.json.Json
+
+/**
+ * A version of [Event] whose arguments have not yet been serialized to JSON and is thus
+ * cheap to create on the UI thread.
+ */
+@Poko
+public class UiEvent(
+  public val id: Id,
+  public val tag: EventTag,
+  public val args: List<Any?> = emptyList(),
+  public val serializationStrategies: List<SerializationStrategy<Any?>> = emptyList(),
+) {
+  init {
+    check(args.size == serializationStrategies.size) {
+      "Properties 'args' and 'serializationStrategies' must have the same size. " +
+        "Found ${args.size} and ${serializationStrategies.size}"
+    }
+  }
+
+  /** Serialize [args] into a JSON model using [serializationStrategies] into an [Event]. */
+  public fun toProtocol(json: Json): Event {
+    return Event(
+      id = id,
+      tag = tag,
+      args = List(args.size) {
+        json.encodeToJsonElement(serializationStrategies[it], args[it])
+      }
+    )
+  }
+}
+
+/** A version of [EventSink] which consumes [UiEvent]s. */
+public fun interface UiEventSink {
+  public fun sendEvent(uiEvent: UiEvent)
+}

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

@@ -18,7 +18,6 @@ package app.cash.redwood.protocol.host
 import app.cash.redwood.Modifier
 import app.cash.redwood.RedwoodCodegenApi
 import app.cash.redwood.protocol.ChildrenTag
-import app.cash.redwood.protocol.EventSink
 import app.cash.redwood.protocol.Id
 import app.cash.redwood.protocol.PropertyChange
 import app.cash.redwood.protocol.WidgetTag
@@ -128,7 +127,7 @@ class ChildrenNodeIndexTest {
 
 @OptIn(RedwoodCodegenApi::class)
 private class WidgetNode(override val widget: StringWidget) : ProtocolNode<String>(Id(1), WidgetTag(1)) {
-  override fun apply(change: PropertyChange, eventSink: EventSink) {
+  override fun apply(change: PropertyChange, eventSink: UiEventSink) {
     throw UnsupportedOperationException()
   }
 

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

@@ -21,7 +21,6 @@ import app.cash.redwood.layout.testing.RedwoodLayoutTestingWidgetFactory
 import app.cash.redwood.lazylayout.testing.RedwoodLazyLayoutTestingWidgetFactory
 import app.cash.redwood.protocol.ChildrenTag
 import app.cash.redwood.protocol.Event
-import app.cash.redwood.protocol.EventSink
 import app.cash.redwood.protocol.EventTag
 import app.cash.redwood.protocol.Id
 import app.cash.redwood.protocol.ModifierElement
@@ -258,7 +257,7 @@ class ProtocolFactoryTest {
     )
     val textInput = factory.createNode(Id(1), WidgetTag(5))!!
 
-    val throwingEventSink = EventSink { error(it) }
+    val throwingEventSink = UiEventSink { error(it) }
     textInput.apply(PropertyChange(Id(1), PropertyTag(2), JsonPrimitive("PT10S")), throwingEventSink)
 
     assertThat((textInput.widget.value as TextInputValue).customType).isEqualTo(10.seconds)
@@ -275,7 +274,7 @@ class ProtocolFactoryTest {
     val button = factory.createNode(Id(1), WidgetTag(4))!!
 
     val change = PropertyChange(Id(1), PropertyTag(345432))
-    val eventSink = EventSink { throw UnsupportedOperationException() }
+    val eventSink = UiEventSink { throw UnsupportedOperationException() }
     val t = assertFailsWith<IllegalArgumentException> {
       button.apply(change, eventSink)
     }
@@ -315,12 +314,12 @@ class ProtocolFactoryTest {
     )
     val textInput = factory.createNode(Id(1), WidgetTag(5))!!
 
-    val eventSink = RecordingEventSink()
+    val eventSink = RecordingUiEventSink()
     textInput.apply(PropertyChange(Id(1), PropertyTag(4), JsonPrimitive(true)), eventSink)
 
     (textInput.widget.value as TextInputValue).onChangeCustomType!!.invoke(10.seconds)
 
-    assertThat(eventSink.events.single())
+    assertThat(eventSink.events.single().toProtocol(json))
       .isEqualTo(Event(Id(1), EventTag(4), listOf(JsonPrimitive("PT10S"))))
   }
 }

redwood-protocol-host/src/commonTest/kotlin/app/cash/redwood/protocol/host/RecordingEventSink.kt → redwood-protocol-host/src/commonTest/kotlin/app/cash/redwood/protocol/host/RecordingUiEventSink.kt

@@ -15,13 +15,10 @@
  */
 package app.cash.redwood.protocol.host
 
-import app.cash.redwood.protocol.Event
-import app.cash.redwood.protocol.EventSink
+class RecordingUiEventSink : UiEventSink {
+  val events = mutableListOf<UiEvent>()
 
-class RecordingEventSink : EventSink {
-  val events = mutableListOf<Event>()
-
-  override fun sendEvent(event: Event) {
-    events += event
+  override fun sendEvent(uiEvent: UiEvent) {
+    events += uiEvent
   }
 }