Enhance ZIndex implementation with availability annotations and improved tests

Example/OpenSwiftUIUITests/Layout/Stack/ZStackIndexUITests.swift

@@ -0,0 +1,40 @@
+//
+//  ZIndexCompatibilityTests.swift
+//  OpenSwiftUICompatibilityTests
+
+import Foundation
+import Testing
+import SnapshotTesting
+
+@MainActor
+@Suite(.snapshots(record: .never, diffTool: diffTool))
+struct ZStackIndexUITests {
+    @Test
+    func zIndexExample() {
+        struct ContentView: View {
+            var body: some View {
+                VStack {
+                    // TODO: Path & Shape is not implemented yet.
+                    Color.yellow
+//                    Rectangle()
+//                        .fill(Color.yellow)
+                        .frame(width: 100, height: 100, alignment: .center)
+                        .zIndex(1) // Top layer.
+                    Color.red
+//                    Rectangle()
+//                        .fill(Color.red)
+                        .frame(width: 100, height: 100, alignment: .center)
+                        .rotationEffect(.degrees(45))
+                        // Here a zIndex of 0 is the default making
+                        // this the bottom layer.
+                }
+            }
+        }
+        withKnownIssue {
+            openSwiftUIAssertSnapshot(
+                of: ContentView(),
+                size: CGSize(width: 200, height: 200)
+            )
+        }
+    }
+}

Sources/OpenSwiftUICore/Layout/Stack/ZIndex.swift

@@ -2,9 +2,10 @@
 //  ZIndex.swift
 //  OpenSwiftUICore
 //
-//  Audited for 6.0.87
+//  Audited for 6.5.4
 //  Status: Complete
 
+@available(OpenSwiftUI_v1_0, *)
 extension View {
     /// Controls the display order of overlapping views.
     ///
@@ -39,6 +40,8 @@ extension View {
     }
 
 }
+
+@available(OpenSwiftUI_v1_0, *)
 @usableFromInline
 package struct ZIndexTraitKey: _ViewTraitKey {
     @inlinable

Tests/OpenSwiftUICoreTests/Layout/ZIndexTests.swift

@@ -3,19 +3,17 @@
 //  OpenSwiftUICoreTests
 
 import OpenAttributeGraphShims
+@_spi(ForOpenSwiftUIOnly)
 import OpenSwiftUICore
 import Testing
 
 @MainActor
 struct ZIndexTests {
     @Test
-    func indexOrder() {
-        struct ContentView: View {
-            var body: some View {
-                Color.red
-                    .zIndex(0.5)
-            }
-        }
-        // TODO: Add a test helper to hook into makeViewList and retrieve the zIndex value to verify it
+    func traitCollectionZIndex() {
+        var collection = ViewTraitCollection()
+        #expect(collection.zIndex.isApproximatelyEqual(to: 0.0))
+        collection.zIndex = 1.5
+        #expect(collection.zIndex.isApproximatelyEqual(to: 1.5))
     }
 }