Test that we don't leak CodeListeners (#2055)

redwood-treehouse-host/src/appsJvmTest/kotlin/app/cash/redwood/treehouse/LeaksTest.kt

@@ -95,7 +95,7 @@ class LeaksTest {
     val view = tester.view()
 
     content.bind(view)
-    content.awaitContent(untilChangeCount = 1)
+    content.awaitContent()
 
     val eventListenerLeakWatcher = LeakWatcher {
       (tester.eventListenerFactory as RetainEverythingEventListenerFactory)
@@ -156,6 +156,36 @@ class LeaksTest {
     treehouseApp.stop()
   }
 
+  @Test
+  fun codeListenerNotLeaked() = runTest {
+    val tester = TreehouseTester(this)
+    val treehouseApp = tester.loadApp()
+    val view = tester.view()
+
+    var codeListener: CodeListener? = RetainEverythingCodeListener(tester.eventLog)
+    val content = treehouseApp.createContent(
+      source = { app -> app.launchForTester() },
+      codeListener = codeListener!!,
+    )
+    val codeListenerLeakWatcher = LeakWatcher { codeListener }
+
+    // Stop referencing the CodeListener from our test harness.
+    codeListener = null
+
+    // One a view is bound, the code listener is in a reference cycle.
+    content.bind(view)
+    tester.eventLog.takeEvent("onCodeLoaded", skipOthers = true)
+    codeListenerLeakWatcher.assertObjectInReferenceCycle()
+
+    // When the view is unbound, the code listener is no longer reachable.
+    content.unbind()
+    tester.eventLog.takeEvent("onCodeDetached", skipOthers = true)
+    treehouseApp.dispatchers.awaitLaunchedTasks()
+    codeListenerLeakWatcher.assertNotLeaked()
+
+    treehouseApp.stop()
+  }
+
   /**
    * This is unfortunate. Some cleanup functions launch jobs on another dispatcher and we don't have
    * a natural way to wait for those jobs to complete. So we launch empty jobs on each dispatcher,

redwood-treehouse-host/src/appsJvmTest/kotlin/app/cash/redwood/treehouse/RetainEverythingCodeListener.kt

@@ -0,0 +1,40 @@
+/*
+ * 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.treehouse
+
+class RetainEverythingCodeListener(
+  private val eventLog: EventLog,
+) : CodeListener() {
+  private var app: TreehouseApp<*>? = null
+  private var view: TreehouseView<*>? = null
+
+  override fun onInitialCodeLoading(app: TreehouseApp<*>, view: TreehouseView<*>) {
+    this.app = app
+    this.view = view
+  }
+
+  override fun onCodeLoaded(app: TreehouseApp<*>, view: TreehouseView<*>, initial: Boolean) {
+    this.app = app
+    this.view = view
+    eventLog += "onCodeLoaded"
+  }
+
+  override fun onCodeDetached(app: TreehouseApp<*>, view: TreehouseView<*>, exception: Throwable?) {
+    this.app = app
+    this.view = view
+    eventLog += "onCodeDetached"
+  }
+}