Fix async renderer inherited view update crash

Example/Shared/Render/Async/AsyncRendererExample.swift

@@ -0,0 +1,59 @@
+//
+//  AsyncRendererExample.swift
+//  Shared
+
+#if OPENSWIFTUI
+import OpenSwiftUI
+#else
+import SwiftUI
+#endif
+
+struct AsyncRendererExample: View {
+    @State private var items = [6]
+
+    var body: some View {
+        VStack(spacing: 10) {
+            ForEach(items, id: \.self) { item in
+                Color.blue.opacity(Double(item) / 6.0)
+                    .frame(height: 50)
+                    .transition(.slide)
+            }
+        }
+        .animation(.easeInOut(duration: 2), value: items)
+        .onAppear {
+            items.removeAll { $0 == 6 }
+        }
+    }
+}
+
+struct AsyncRendererTransitionExample: View {
+    @State private var isVisible: Bool = false
+
+    var body: some View {
+        Group {
+            if isVisible {
+                Color.red
+                    .frame(width: 80, height: 80)
+                    .clipShape(RoundedRectangle(cornerRadius: 0))
+                    .transition(RenderCrashTransition())
+            }
+        }
+        .frame(width: 200, height: 200)
+        .animation(.linear(duration: 1), value: isVisible)
+        .onAppear {
+            guard !isVisible else {
+                return
+            }
+            isVisible = true
+        }
+    }
+
+    // This custom transition forces the async renderer to update inherited view
+    // content while a transition phase is changing. It covers the path that used
+    // to trip Swift's exclusivity checks in DisplayList.ViewUpdater.
+    private struct RenderCrashTransition: Transition {
+        func body(content: Content, phase: TransitionPhase) -> some View {
+            content.opacity(phase.isIdentity ? 1 : 0.1)
+        }
+    }
+}

Sources/OpenSwiftUI/Integration/Hosting/AppKit/View/NSHostingView.swift

@@ -859,8 +859,25 @@ extension NSHostingView {
     }
 
     public func _renderAsyncForTest(interval: Double) -> Bool {
-        _openSwiftUIUnimplementedWarning()
-        return false
+        advanceTimeForTest(interval: interval)
+        canAdvanceTimeAutomatically = false
+        var result = true
+        repeat {
+            RunLoop.flushObservers()
+            let didRender = Update.locked {
+                renderAsync(targetTimestamp: nil) != nil
+            }
+            if didRender {
+                CATransaction.flush()
+                if result {
+                    result = !viewGraph.updateRequiredMainThread
+                }
+            } else {
+                result = false
+            }
+        } while !propertiesNeedingUpdate.isEmpty
+        canAdvanceTimeAutomatically = true
+        return result
     }
 }
 

Sources/OpenSwiftUICore/Render/DisplayList/DisplayListViewUpdater.swift

@@ -393,7 +393,7 @@ extension DisplayList {
                             newItem: newItem,
                             newState: newStatePtr,
                             tag: .inherited
-                        ) { layer, _, oldItem, oldState, newItem, newState in
+                        ) { [platform] layer, _, oldItem, oldState, newItem, newState in
                             platform.updateInheritedLayerAsync(
                                 layer: &layer,
                                 oldItem: oldItem,