WIP: Break more cycles in widget bindings

The ProtocolNode is a Kotlin object and the Widget is potentially
a Swift object. This introduces a potential retain cycle problem.

redwood-lazylayout-uiview/src/commonMain/kotlin/app/cash/redwood/lazylayout/uiview/UIViewLazyList.kt

@@ -65,7 +65,7 @@ import platform.UIKit.item
 import platform.darwin.NSInteger
 import platform.darwin.NSObject
 
-internal open class UIViewLazyList() : LazyList<UIView>, ChangeListener {
+internal open class UIViewLazyList : LazyList<UIView>, ChangeListener {
   internal val tableView: UITableView = object : UITableView(
     CGRectZero.readValue(),
     UITableViewStyle.UITableViewStylePlain,
@@ -94,6 +94,10 @@ internal open class UIViewLazyList() : LazyList<UIView>, ChangeListener {
       }
     }
 
+    override fun isSizeOnlyPlaceholder(placeholder: UIView): Boolean {
+      return false // TODO
+    }
+
     override fun insertRows(index: Int, count: Int) {
       // TODO(jwilson): pass a range somehow when 'count' is large?
       tableView.beginUpdates()
@@ -118,7 +122,7 @@ internal open class UIViewLazyList() : LazyList<UIView>, ChangeListener {
       tableView.endUpdates()
     }
 
-    override fun setContent(view: LazyListContainerCell, content: Widget<UIView>?) {
+    override fun setContent(view: LazyListContainerCell, content: UIView?) {
       view.content = content
     }
   }
@@ -269,13 +273,13 @@ internal class LazyListContainerCell(
   reuseIdentifier: String?,
 ) : UITableViewCell(style, reuseIdentifier) {
   internal var binding: Binding<LazyListContainerCell, UIView>? = null
-  internal var content: Widget<UIView>? = null
+  internal var content: UIView? = null
     set(value) {
       field = value
 
       removeAllSubviews()
       if (value != null) {
-        contentView.addSubview(value.value)
+        contentView.addSubview(value)
       }
       setNeedsLayout()
     }
@@ -319,12 +323,12 @@ internal class LazyListContainerCell(
     super.layoutSubviews()
 
     val content = this.content ?: return
-    content.value.setFrame(bounds)
+    content.setFrame(bounds)
     contentView.setFrame(bounds)
   }
 
   override fun sizeThatFits(size: CValue<CGSize>): CValue<CGSize> {
-    return content?.value?.sizeThatFits(size) ?: return super.sizeThatFits(size)
+    return content?.sizeThatFits(size) ?: return super.sizeThatFits(size)
   }
 
   private fun removeAllSubviews() {

redwood-lazylayout-widget/src/commonMain/kotlin/app/cash/redwood/lazylayout/widget/LazyListUpdateProcessor.kt

@@ -42,7 +42,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
     get() = itemsBefore.nonNullElements + loadedItems + itemsAfter.nonNullElements
 
   /** Pool of placeholder widgets. */
-  private val placeholdersQueue = ArrayDeque<Widget<W>>()
+  private val placeholdersQueue = ArrayDeque<W>()
 
   /**
    * The first placeholder ever returned. We use it to choose measured dimensions for created
@@ -69,7 +69,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
     override fun insert(index: Int, widget: Widget<W>) {
       _widgets += widget
       if (firstPlaceholder == null) firstPlaceholder = widget
-      placeholdersQueue += widget
+      placeholdersQueue += widget.value
     }
 
     override fun move(fromIndex: Int, toIndex: Int, count: Int) {
@@ -82,6 +82,10 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
 
     override fun onModifierUpdated(index: Int, widget: Widget<W>) {
     }
+
+    override fun disconnect() {
+      _widgets.clear()
+    }
   }
 
   /** Changes to this list are collected and processed in batch once all changes are received. */
@@ -120,6 +124,10 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
       }
     }
 
+    override fun disconnect() {
+      _widgets.clear()
+    }
+
     override fun onModifierUpdated(index: Int, widget: Widget<W>) {
     }
   }
@@ -168,7 +176,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
         val toPromoteCount = minOf(edit.widgets.size, itemsBefore.size - newItemsBefore)
         for (i in edit.widgets.size - 1 downTo edit.widgets.size - toPromoteCount) {
           val placeholder = itemsBefore.removeLast()
-          loadedItems.add(0, placeholderToLoaded(placeholder, edit.widgets[i]))
+          loadedItems.add(0, placeholderToLoaded(placeholder, edit.widgets[i].value))
           edit.widgets.removeAt(i)
         }
       } else if (
@@ -197,7 +205,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
         for (i in 0 until toPromoteCount) {
           val widget = edit.widgets.removeFirst()
           val placeholder = itemsAfter.removeAt(0)
-          loadedItems.add(placeholderToLoaded(placeholder, widget))
+          loadedItems.add(placeholderToLoaded(placeholder, widget.value))
           edit.index++
         }
       } else if (
@@ -220,7 +228,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
           for (i in 0 until edit.widgets.size) {
             val index = itemsBefore.size + edit.index + i
             val binding = Binding(this).apply {
-              content = edit.widgets[i]
+              content = edit.widgets[i].value
             }
             loadedItems.add(edit.index + i, binding)
 
@@ -307,7 +315,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
 
   private fun placeholderToLoaded(
     placeholder: Binding<V, W>?,
-    loadedContent: Widget<W>,
+    loadedContent: W,
   ): Binding<V, W> {
     // No binding for this index. Create one.
     if (placeholder == null) {
@@ -377,18 +385,18 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
     }
   }
 
-  private fun takePlaceholder(): Widget<W> {
+  private fun takePlaceholder(): W {
     val result = placeholdersQueue.removeFirstOrNull()
     if (result != null) return result
 
-    val created = createPlaceholder(firstPlaceholder!!.value)
+    return createPlaceholder(firstPlaceholder!!.value)
       ?: throw IllegalStateException("no more placeholders!")
-
-    return SizeOnlyPlaceholder(created)
   }
 
-  private fun recyclePlaceholder(placeholder: Widget<W>) {
-    if (placeholder !is SizeOnlyPlaceholder) {
+  protected abstract fun isSizeOnlyPlaceholder(placeholder: W): Boolean
+
+  private fun recyclePlaceholder(placeholder: W) {
+    if (!isSizeOnlyPlaceholder(placeholder)) {
       placeholdersQueue += placeholder
     }
   }
@@ -411,7 +419,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
 
   protected abstract fun deleteRows(index: Int, count: Int)
 
-  protected abstract fun setContent(view: V, content: Widget<W>?)
+  protected abstract fun setContent(view: V, content: W?)
 
   /**
    * Binds a UI-managed view to model-managed content.
@@ -440,7 +448,7 @@ public abstract class LazyListUpdateProcessor<V : Any, W : Any> {
      * The content of this binding; either a loaded widget or a placeholder. This should be
      * `lateinit`, but it can't be because of the side-effect in set().
      */
-    internal var content: Widget<W>? = null
+    internal var content: W? = null
       set(value) {
         field = value
         val view = this.view

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

@@ -164,6 +164,13 @@ public class ProtocolBridge<W : Any>(
    */
   public fun close() {
     closed = true
+    for (node in nodes.values) {
+      for (childrenTag in factory.widgetChildren(node.widgetTag)) {
+        val children = node.children(childrenTag) ?: continue
+        children.nodes.clear()
+        children.children.disconnect()
+      }
+    }
     nodes.clear()
     pool.clear()
   }

redwood-widget/src/commonMain/kotlin/app/cash/redwood/widget/MutableListChildren.kt

@@ -44,4 +44,8 @@ public class MutableListChildren<W : Any>(
   override fun onModifierUpdated(index: Int, widget: Widget<W>) {
     modifierUpdated()
   }
+
+  override fun disconnect() {
+    container.clear()
+  }
 }

redwood-widget/src/commonMain/kotlin/app/cash/redwood/widget/Widget.kt

@@ -69,5 +69,8 @@ public interface Widget<W : Any> {
 
     /** Indicates that [Modifier]s for the child widgets have changed. */
     public fun onModifierUpdated(index: Int, widget: Widget<W>)
+
+    public fun disconnect() {
+    }
   }
 }

redwood-widget/src/iosMain/kotlin/app/cash/redwood/widget/UIViewChildren.kt

@@ -71,6 +71,10 @@ public class UIViewChildren(
   private fun invalidate() {
     (container.superview ?: container).setNeedsLayout()
   }
+
+  override fun disconnect() {
+    _widgets.clear()
+  }
 }
 
 private fun List<UIView>.remove(index: Int, count: Int): Array<UIView> {