Fix CollectionViewLayout delegate lifetime and ListView teardown crash

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Fixed
 
+- Fixed a crash in `CollectionViewLayout` when the delegate was deallocated before the layout. The delegate is now held weakly rather than unowned.
+
 ### Added
 
 ### Removed

ListableUI/Sources/Layout/CollectionViewLayout.swift

@@ -14,7 +14,7 @@ final class CollectionViewLayout : UICollectionViewLayout
     // MARK: Properties
     //
 
-    unowned let delegate : CollectionViewLayoutDelegate
+    private(set) weak var delegate : CollectionViewLayoutDelegate?
 
     var layoutDescription : LayoutDescription
 
@@ -197,7 +197,7 @@ final class CollectionViewLayout : UICollectionViewLayout
         self.neededLayoutType.merge(with: context)
     }
 
-    private func sendEndQueuingEditsAfterDelay() {
+    func sendEndQueuingEditsAfterDelay() {
 
         ///
         /// Hello! Welcome to the source code. You're probably wondering why this perform after runloop hack is here.
@@ -221,8 +221,10 @@ final class CollectionViewLayout : UICollectionViewLayout
         /// processing any further updates 🥴.
         ///
 
-        OperationQueue.main.addOperation {
-            self.delegate.listViewShouldEndQueueingEditsForReorder()
+        let delegate = self.delegate
+
+        OperationQueue.main.addOperation { [weak delegate] in
+            delegate?.listViewShouldEndQueueingEditsForReorder()
         }
     }
 
@@ -390,6 +392,10 @@ final class CollectionViewLayout : UICollectionViewLayout
 
         self.changesDuringCurrentUpdate = UpdateItems(with: [])
 
+        guard let delegate = self.delegate else {
+            return
+        }
+
         let size = self.collectionView?.bounds.size ?? .zero
 
         self.neededLayoutType.update(with: {
@@ -402,18 +408,18 @@ final class CollectionViewLayout : UICollectionViewLayout
             case .none:
                 return true
             case .relayout:
-                self.performLayout()
+                self.performLayout(delegate: delegate)
             case .rebuild:
-                self.performRebuild(andLayout: shouldLayout)
+                self.performRebuild(andLayout: shouldLayout, delegate: delegate)
             }
 
             return true
         }())
 
-        self.performLayoutUpdate()
+        self.performLayoutUpdate(delegate: delegate)
 
         if self.isReordering == false {
-            self.delegate.listViewLayoutDidLayoutContents()
+            delegate.listViewLayoutDidLayoutContents()
         }
     }
 
@@ -439,15 +445,15 @@ final class CollectionViewLayout : UICollectionViewLayout
     // MARK: Performing Layouts
     //
 
-    private func performRebuild(andLayout layout : Bool)
+    private func performRebuild(andLayout layout : Bool, delegate : CollectionViewLayoutDelegate)
     {
         self.previousLayout = self.layout
 
         self.layout = self.layoutDescription.configuration.createPopulatedLayout(
             appearance: self.appearance,
             behavior: self.behavior,
             content: {
-                self.delegate.listLayoutContent(defaults: $0)
+                delegate.listLayoutContent(defaults: $0)
             }
         )
 
@@ -459,34 +465,34 @@ final class CollectionViewLayout : UICollectionViewLayout
         )
 
         if layout {
-            self.performLayout()
+            self.performLayout(delegate: delegate)
         }
     }
 
-    private func performLayout()
+    private func performLayout(delegate : CollectionViewLayoutDelegate)
     {
         let view = self.collectionView!
 
         let context = ListLayoutLayoutContext(
             collectionView: view,
-            environment: self.delegate.listViewLayoutCurrentEnvironment()
+            environment: delegate.listViewLayoutCurrentEnvironment()
         )
 
         self.layout.performLayout(
-            with: self.delegate,
+            with: delegate,
             in: context
         )
 
         self.viewProperties = CollectionViewLayoutProperties(collectionView: view)
     }
 
-    private func performLayoutUpdate()
+    private func performLayoutUpdate(delegate : CollectionViewLayoutDelegate)
     {
         let view = self.collectionView!
 
         let context = ListLayoutLayoutContext(
             collectionView: view,
-            environment: self.delegate.listViewLayoutCurrentEnvironment()
+            environment: delegate.listViewLayoutCurrentEnvironment()
         )
 
         self.layout.positionStickyListHeaderIfNeeded(in: context)

ListableUI/Sources/ListView/ListView.LayoutManager.swift

@@ -45,8 +45,12 @@ extension ListView
                     self.collectionViewLayout.setNeedsRebuild(animated: animated)
                 }
             } else {
+                guard let delegate = self.collectionViewLayout.delegate else {
+                    listableInternalFatal("Cannot swap layout when the previous layout's delegate has been deallocated.")
+                }
+
                 self.collectionViewLayout = CollectionViewLayout(
-                    delegate: self.collectionViewLayout.delegate,
+                    delegate: delegate,
                     layoutDescription: layout,
                     appearance: self.collectionViewLayout.appearance,
                     behavior: self.collectionViewLayout.behavior

ListableUI/Sources/ListView/ListView.swift

@@ -151,6 +151,8 @@ public final class ListView : UIView
 
         self.collectionView.delegate = nil
         self.collectionView.dataSource = nil
+
+        self.collectionView.removeFromSuperview()
     }
 
     @available(*, unavailable)
@@ -1111,9 +1113,13 @@ public final class ListView : UIView
     public override func didMoveToWindow()
     {
         super.didMoveToWindow()
-        
+
         if self.window != nil {
             self.updateScrollViewInsets()
+        } else {
+            self.collectionView.delegate = nil
+            self.collectionView.dataSource = nil
+            self.collectionView.removeFromSuperview()
         }
     }
 

ListableUI/Tests/Layout/CollectionViewLayoutTests.swift

@@ -0,0 +1,85 @@
+//
+//  CollectionViewLayoutTests.swift
+//  ListableUI-Unit-Tests
+//
+//  Created by Alex Odawa on 5/2/26.
+//
+
+import XCTest
+@testable import ListableUI
+
+
+final class CollectionViewLayoutTests : XCTestCase
+{
+    func test_prepare_whenDelegateHasBeenDeallocated()
+    {
+        weak var weakDelegate : CollectionViewLayoutDelegateMock?
+
+        let layout : CollectionViewLayout = {
+            let delegate = CollectionViewLayoutDelegateMock()
+            weakDelegate = delegate
+
+            return CollectionViewLayout(
+                delegate: delegate,
+                layoutDescription: .table(),
+                appearance: Appearance(),
+                behavior: Behavior()
+            )
+        }()
+
+        XCTAssertNil(weakDelegate)
+        XCTAssertNil(layout.delegate)
+
+        layout.prepare()
+    }
+
+    /// Exercises the real production path that motivates the weak-delegate fix:
+    /// `sendEndQueuingEditsAfterDelay` schedules a closure on `OperationQueue.main`
+    /// that fires on a later runloop turn. If the owning `ListView` (and therefore
+    /// the delegate) deallocates between scheduling and dispatch, the closure
+    /// previously trapped on the `unowned` delegate access.
+    func test_sendEndQueuingEditsAfterDelay_whenDelegateDeallocatesBeforeDispatch()
+    {
+        weak var weakDelegate : CollectionViewLayoutDelegateMock?
+
+        autoreleasepool {
+            let delegate = CollectionViewLayoutDelegateMock()
+            weakDelegate = delegate
+
+            let layout = CollectionViewLayout(
+                delegate: delegate,
+                layoutDescription: .table(),
+                appearance: Appearance(),
+                behavior: Behavior()
+            )
+
+            layout.sendEndQueuingEditsAfterDelay()
+        }
+
+        XCTAssertNil(weakDelegate)
+
+        let drained = expectation(description: "main queue drained")
+        OperationQueue.main.addOperation { drained.fulfill() }
+        wait(for: [drained], timeout: 1.0)
+    }
+}
+
+
+private final class CollectionViewLayoutDelegateMock : CollectionViewLayoutDelegate
+{
+    func listViewLayoutUpdatedItemPositions() {}
+
+    func listLayoutContent(
+        defaults: ListLayoutDefaults
+    ) -> ListLayoutContent {
+        ListLayoutContent()
+    }
+
+    func listViewLayoutCurrentEnvironment() -> ListEnvironment {
+        .empty
+    }
+
+    func listViewLayoutDidLayoutContents() {}
+
+    func listViewShouldEndQueueingEditsForReorder() {}
+}