Add layoutPriority support (#337)

* Implement LayoutPriority

* Add layoutPriority and overlayAndBackground test case

* Fix overlay and makeSecondaryLayerView bug

* Update Example VC

Author: Kyle-Ye

Example/Example.xcodeproj/xcshareddata/xcschemes/OpenSwiftUIUITests.xcscheme

@@ -8,7 +8,7 @@
       buildArchitectures = "Automatic">
    </BuildAction>
    <TestAction
-      buildConfiguration = "OpenSwiftUIDebug"
+      buildConfiguration = "SwiftUIDebug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
       shouldUseLaunchSchemeArgsEnv = "YES">

Example/HostingExample/ViewController.swift

@@ -66,7 +66,18 @@ class ViewController: NSViewController {
 
 struct ContentView: View {
     var body: some View {
-        Color.red
-            .frame(width: 200, height: 200)
+        ZStack(alignment: .leading) {
+            Color.red
+                .opacity(0.5)
+                .frame(width: 200, height: 200)
+        }
+        .overlay(alignment: .topLeading) {
+            Color.green.opacity(0.5)
+                .frame(width: 100, height: 100)
+        }
+        .background(alignment: .bottomTrailing) {
+            Color.blue.opacity(0.5)
+                .frame(width: 100, height: 100)
+        }
     }
 }

Example/OpenSwiftUIUITests/Layout/Stack/ZStackUITests.swift

@@ -40,5 +40,54 @@ struct ZStackUITests {
         )
     }
 
-    // TODO: layoutPriority
+    @Test
+    func layoutPriority() {
+        struct ContentView: View {
+            var body: some View {
+                ZStack(alignment: .leading) {
+                    Color.blue
+                        .opacity(0.5)
+                        .frame(width: 100, height: 100)
+                        .layoutPriority(-0.1)
+                    Color.red
+                        .opacity(0.5)
+                        .frame(width: 60, height: 60)
+                    Color.green
+                        .frame(width: 40, height: 40)
+                        .layoutPriority(1)
+                }
+                .overlay {
+                    Color.black
+                        .frame(width: 20, height: 20)
+                }
+            }
+        }
+        openSwiftUIAssertSnapshot(
+            of: ContentView()
+        )
+    }
+
+    @Test
+    func overlayAndBackground() {
+        struct ContentView: View {
+            var body: some View {
+                ZStack(alignment: .leading) {
+                    Color.red
+                        .opacity(0.5)
+                        .frame(width: 200, height: 200)
+                }
+                .overlay(alignment: .topLeading) {
+                    Color.green.opacity(0.5)
+                        .frame(width: 100, height: 100)
+                }
+                .background(alignment: .bottomTrailing) {
+                    Color.blue.opacity(0.5)
+                        .frame(width: 100, height: 100)
+                }
+            }
+        }
+        openSwiftUIAssertSnapshot(
+            of: ContentView()
+        )
+    }
 }

Sources/OpenSwiftUICore/Layout/Stack/LayoutPriorityLayout.swift renamed to Sources/OpenSwiftUICore/Layout/LayoutPriority.swift

@@ -1,12 +1,14 @@
 //
-//  LayoutPriorityLayout.swift
+//  LayoutPriority.swift
 //  OpenSwiftUICore
 //
-//  Audited for iOS 18.0
-//  Status: WIP
+//  Status: Complete
 
 package import Foundation
 
+// MARK: - View + layoutPriority [6.4.41]
+
+@available(OpenSwiftUI_v1_0, *)
 extension View {
     /// Sets the priority by which a parent layout should apportion space to
     /// this child.
@@ -49,6 +51,8 @@ extension View {
     }
 }
 
+// MARK: - LayoutPriorityTraitKey [6.4.41]
+
 @usableFromInline
 package struct LayoutPriorityTraitKey: _ViewTraitKey {
     @inlinable
@@ -58,17 +62,36 @@ package struct LayoutPriorityTraitKey: _ViewTraitKey {
 @available(*, unavailable)
 extension LayoutPriorityTraitKey: Sendable {}
 
-// FIXME
+// MARK: - LayoutPriorityLayout [6.4.41]
+
 package struct LayoutPriorityLayout: UnaryLayout {
+    package init(priority: Double) {
+        self.priority = priority
+    }
+
     package func placement(of child: LayoutProxy, in context: PlacementContext) -> _Placement {
-        preconditionFailure("TODO")
+        _Placement(
+            proposedSize: context.proposedSize,
+            aligning: .center,
+            in: context.size
+        )
     }
 
     package func sizeThatFits(in proposedSize: _ProposedSize, context: SizeAndSpacingContext, child: LayoutProxy) -> CGSize {
-        preconditionFailure("TODO")
+        child.size(in: proposedSize)
     }
-    
-    package static func makeViewImpl(modifier: _GraphValue<LayoutPriorityLayout>, inputs: _ViewInputs, body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs) -> _ViewOutputs {
-        .init()
+
+    package func spacing(in context: SizeAndSpacingContext, child: LayoutProxy) -> Spacing {
+        child.spacing()
+    }
+
+    package func layoutPriority(child: LayoutProxy) -> Double {
+        priority
     }
+
+    package func ignoresAutomaticPadding(child: LayoutProxy) -> Bool {
+        child.ignoresAutomaticPadding
+    }
+
+    package var priority: Double
 }

Sources/OpenSwiftUICore/Modifier/ViewModifier/OverlayModifier.swift

@@ -45,8 +45,8 @@ package func makeSecondaryLayerView<SecondaryLayer>(
         key.visitKey(&visitor)
     }
     var result = visitor.result
-    result.layoutComputer = secondaryOutputs.layoutComputer
-    return visitor.result
+    result.layoutComputer = primaryOutputs.layoutComputer
+    return result
 }
 
 // MARK: - OverlayModifier [6.4.41]
@@ -208,7 +208,7 @@ extension View {
     /// - Returns: A view that uses the specified content as a foreground.
     @inlinable
     nonisolated public func overlay<V>(alignment: Alignment = .center, @ViewBuilder content: () -> V) -> some View where V: View {
-        modifier(_BackgroundModifier(background: content(), alignment: alignment))
+        modifier(_OverlayModifier(overlay: content(), alignment: alignment))
     }
 }
 

Sources/OpenSwiftUICore/View/Graph/ViewGraph.swift

@@ -159,7 +159,10 @@ package final class ViewGraph: GraphHost {
         // _inheritedPhase
         _gestureResetSeed = Attribute(value: .zero)
         _gesturePreferenceKeys = Attribute(value: .init())
-        _rootGeometry = Attribute(RootGeometry(proposedSize: _proposedSize, safeAreaInsets: OptionalAttribute(_safeAreaInsets)))
+        _rootGeometry = Attribute(RootGeometry(
+            proposedSize: _proposedSize,
+            safeAreaInsets: OptionalAttribute(_safeAreaInsets)
+        ))
         _position = _rootGeometry.origin()
         _dimensions = _rootGeometry.size()
         makeRootView = { [_zeroPoint, _proposedSize, _safeAreaInsets] view, inputs in
@@ -236,7 +239,7 @@ package final class ViewGraph: GraphHost {
                 as: RootGeometry.self,
                 invalidating: true
             ) { rootGeometry in
-                rootGeometry.$layoutDirection = inputs.mapEnvironment(id: .layoutDirection) { $0.layoutDirection }
+                rootGeometry.$layoutDirection = inputs.layoutDirection
             }
             for feature in features {
                 feature.modifyViewInputs(inputs: &inputs, graph: self)