Add UnaryLayout

Author: Kyle-Ye

Sources/OpenSwiftUICore/Layout/Stack/LayoutPriorityLayout.swift

@@ -5,6 +5,8 @@
 //  Audited for iOS 18.0
 //  Status: WIP
 
+package import Foundation
+
 extension View {
     /// Sets the priority by which a parent layout should apportion space to
     /// this child.
@@ -56,18 +58,17 @@ package struct LayoutPriorityTraitKey: _ViewTraitKey {
 @available(*, unavailable)
 extension LayoutPriorityTraitKey: Sendable {}
 
-// FIXME
-protocol UnaryLayout: ViewModifier {
-    static func makeViewImpl(
-        modifier: _GraphValue<Self>,
-        inputs: _ViewInputs,
-        body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs
-    ) -> _ViewOutputs
-}
-
 // FIXME
 package struct LayoutPriorityLayout: UnaryLayout {
-    static func makeViewImpl(modifier: _GraphValue<LayoutPriorityLayout>, inputs: _ViewInputs, body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs) -> _ViewOutputs {
+    package func placement(of child: LayoutProxy, in context: PlacementContext) -> _Placement {
+        preconditionFailure("TODO")
+    }
+    
+    package func sizeThatFits(in proposedSize: _ProposedSize, context: SizeAndSpacingContext, child: LayoutProxy) -> CGSize {
+        preconditionFailure("TODO")
+    }
+    
+    package static func makeViewImpl(modifier: _GraphValue<LayoutPriorityLayout>, inputs: _ViewInputs, body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs) -> _ViewOutputs {
         .init()
     }
 }

Sources/OpenSwiftUICore/Layout/UnaryLayout.swift

@@ -0,0 +1,50 @@
+//
+//  UnaryLayout.swift
+//  OpenSwiftUICore
+//
+//  Audited for iOS 18.0
+//  Status: WIP
+
+package import Foundation
+
+package protocol UnaryLayout: Animatable, MultiViewModifier, PrimitiveViewModifier {
+    associatedtype PlacementContextType = PlacementContext
+
+    func spacing(in context: SizeAndSpacingContext, child: LayoutProxy) -> Spacing
+
+    func placement(of child: LayoutProxy, in context: PlacementContextType) -> _Placement
+
+    func sizeThatFits(in proposedSize: _ProposedSize, context: SizeAndSpacingContext, child: LayoutProxy) -> CGSize
+
+    func layoutPriority(child: LayoutProxy) -> Double
+
+    func ignoresAutomaticPadding(child: LayoutProxy) -> Bool
+
+    static func makeViewImpl(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewInputs,
+        body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs
+    ) -> _ViewOutputs
+}
+
+extension UnaryLayout {
+    package func layoutPriority(child: LayoutProxy) -> Double {
+        child.layoutPriority
+    }
+
+    package func ignoresAutomaticPadding(child: LayoutProxy) -> Bool {
+        false
+    }
+
+    nonisolated public static func _makeView(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewInputs,
+        body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs
+    ) -> _ViewOutputs {
+        makeViewImpl(modifier: modifier, inputs: inputs, body: body)
+    }
+
+    package func spacing(in context: SizeAndSpacingContext, child: LayoutProxy) -> Spacing {
+        child.spacing()
+    }
+}