Update VariadicView

Sources/OpenSwiftUI/Core/View/ConditionalContent.swift

@@ -30,9 +30,9 @@ extension _ConditionalContent: View, PrimitiveView where TrueContent: View, Fals
 
     public static func _makeView(view: _GraphValue<Self>, inputs: _ViewInputs) -> _ViewOutputs {
         if _SemanticFeature_v2.isEnable {
-            return makeImplicitRoot(view: view, inputs: inputs)
+            makeImplicitRoot(view: view, inputs: inputs)
         } else {
-            return AnyView._makeView(
+            AnyView._makeView(
                 view: _GraphValue(ChildView(content: view.value)),
                 inputs: inputs
             )

Sources/OpenSwiftUI/Core/View/VariadicView/VariadicView.swift

@@ -0,0 +1,49 @@
+/// A type of structured content that is passed as an argument to a
+/// `Root`'s result builder, creating a `Tree` that conditionally conforms
+/// to protocols like `View`.
+///
+/// For example, `View`s  can be passed to a `Layout` result builder
+/// creating a `View`:
+///
+///     HStack {
+///         Image(name: "envelope")
+///         Text("Your time away request has been approved")
+///         Spacer()
+///         Text(timestamp, format: .dateTime).layoutPriority(1)
+///     }
+///     
+public enum _VariadicView {
+    public typealias Root = _VariadicView_Root
+    public typealias ViewRoot = _VariadicView_ViewRoot
+    public typealias Children = _VariadicView_Children
+//    public typealias UnaryViewRoot = _VariadicView_UnaryViewRoot
+//    public typealias MultiViewRoot = _VariadicView_MultiViewRoot
+
+    @frozen
+    public struct Tree<Root: _VariadicView_Root, Content> {
+        public var root: Root
+        public var content: Content
+        @inlinable
+        init(root: Root, content: Content) {
+            self.root = root
+            self.content = content
+        }
+
+        @inlinable public init(_ root: Root, @ViewBuilder content: () -> Content) {
+            self.root = root
+            self.content = content()
+        }
+    }
+}
+
+extension _VariadicView_ViewRoot {
+    func bodyError() -> Never {
+        fatalError("body() should not be called on \(Self.self)")
+    }
+}
+
+extension _VariadicView_ViewRoot where Body == Never {
+    public func body(children: _VariadicView.Children) -> Never {
+        bodyError()
+    }
+}

Sources/OpenSwiftUI/Core/View/VariadicView/VariadicView_Children.swift

@@ -0,0 +1,6 @@
+// TODO
+
+/// An ad hoc collection of the children of a variadic view.
+public struct _VariadicView_Children {
+
+}

Sources/OpenSwiftUI/Core/View/VariadicView/VariadicView_ImplicitRoot.swift

@@ -0,0 +1,24 @@
+//
+//  VariadicView_ImplicitRoot.swift
+//  OpenSwiftUI
+//
+//  Audited for RELEASE_2021
+//  Status: Complete
+
+protocol _VariadicView_AnyImplicitRoot {
+    func visitType<Visitor: _VariadicView_ImplicitRootVisitor>(visitor: inout Visitor)
+}
+
+protocol _VariadicView_ImplicitRootVisitor {
+    func visit<Root: _VariadicView_ImplicitRoot>(type: Root.Type)
+}
+
+protocol _VariadicView_ImplicitRoot: _VariadicView_AnyImplicitRoot, _VariadicView_ViewRoot {
+    static var implicitRoot: Self { get }
+}
+
+extension _VariadicView_ImplicitRoot {
+    func visitType<Visitor: _VariadicView_ImplicitRootVisitor>(visitor: inout Visitor) {
+        visitor.visit(type: Self.self)
+    }
+}

Sources/OpenSwiftUI/Core/View/VariadicView/VariadicView_Root.swift

@@ -0,0 +1,26 @@
+//
+//  VariadicView_ImplicitRoot.swift
+//  OpenSwiftUI
+//
+//  Audited for RELEASE_2021
+//  Status: Complete
+
+/// A type that creates a `Tree`, managing content subtrees passed to a result builder.
+///
+/// - SeeAlso: _VariadicView.Root.
+public protocol _VariadicView_Root {
+    static var _viewListOptions: Int { get }
+}
+
+extension _VariadicView_Root {
+    public static var _viewListOptions: Int {
+        0
+    }
+
+    public static func _viewListCount(
+        inputs _: _ViewListCountInputs,
+        body _: (_ViewListCountInputs) -> Int?
+    ) -> Int? {
+        nil
+    }
+}

Sources/OpenSwiftUI/Core/View/VariadicView/VariadicView_ViewRoot.swift

@@ -0,0 +1,82 @@
+//
+//  VariadicView_ImplicitRoot.swift
+//  OpenSwiftUI
+//
+//  Audited for RELEASE_2021
+//  Status: WIP
+
+internal import OpenGraphShims
+
+/// A type of root that creates a `View` when its result builder is invoked with
+///  `View`.
+/// - SeeAlso: _VariadicView.ViewRoot.
+/// - Note: Requirements mirror `View`'s.
+public protocol _VariadicView_ViewRoot: _VariadicView_Root {
+    associatedtype Body: View
+
+    static func _makeView(
+        root: _GraphValue<Self>,
+        inputs: _ViewInputs,
+        body: (_Graph, _ViewInputs) -> _ViewListOutputs
+    ) -> _ViewOutputs
+
+    static func _makeViewList(
+        root: _GraphValue<Self>,
+        inputs: _ViewListInputs,
+        body: @escaping (_Graph, _ViewListInputs) -> _ViewListOutputs
+    ) -> _ViewListOutputs
+
+    static func _viewListCount(
+        inputs: _ViewListCountInputs,
+        body: (_ViewListCountInputs) -> Int?
+    ) -> Int?
+
+    @ViewBuilder
+    func body(children: _VariadicView.Children) -> Body
+}
+
+extension _VariadicView_ViewRoot {
+    public static func _makeView(
+        root: _GraphValue<Self>,
+        inputs: _ViewInputs,
+        body: (_Graph, _ViewInputs) -> _ViewListOutputs
+    ) -> _ViewOutputs {
+        fatalError("TODO")
+    }
+
+    public static func _makeViewList(
+        root: _GraphValue<Self>,
+        inputs: _ViewListInputs,
+        body: @escaping (_Graph, _ViewListInputs) -> _ViewListOutputs
+    ) -> _ViewListOutputs {
+        fatalError("TODO")
+    }
+
+    public static func _viewListCount(inputs: _ViewListCountInputs) -> Int? {
+        Body._viewListCount(inputs: inputs)
+    }
+}
+
+
+// MARK: - ViewRootBody
+
+private struct ViewRootBody<Root> {
+    @Attribute var root: Root
+    @Attribute var list: ViewList
+    let contentSubgraph: OGSubgraph
+}
+
+extension _ViewInputs {
+    private struct ImplicitRootType: ViewInput {
+        static let defaultValue: _VariadicView_AnyImplicitRoot.Type = _VStackLayout.self
+    }
+}
+
+extension View {
+    static func makeImplicitRoot(view: _GraphValue<Self>, inputs: _ViewInputs) -> _ViewOutputs {
+        // TODO
+        return .init()
+    }
+}
+
+// TODO: ViewModifier

Sources/OpenSwiftUI/Core/View/ViewList/ViewListCountInputs.swift

@@ -7,9 +7,9 @@
 
 /// Input values to `View._viewListCount()`.
 public struct _ViewListCountInputs {
-    var customInputs : PropertyList
-    var options : _ViewListInputs.Options
-    var baseOptions : _GraphInputs.Options
+    var customInputs: PropertyList
+    var options: _ViewListInputs.Options
+    var baseOptions: _GraphInputs.Options
 
     subscript<Input: GraphInput>(_ type: Input.Type) -> Input.Value {
         get { customInputs[type] }

Sources/OpenSwiftUI/Core/View/ViewRoot.swift

@@ -6,9 +6,3 @@
 //  Status: WIP
 //  ID: 00F12C0E37A19C593ECA0DBD3BE26541
 
-extension View {
-    static func makeImplicitRoot(view: _GraphValue<Self>, inputs: _ViewInputs) -> _ViewOutputs {
-        // TODO
-        return .init()
-    }
-}

Sources/OpenSwiftUI/Layout/LayoutFundamentals/Stack/HVStackLayout.swift

@@ -0,0 +1,38 @@
+import Foundation
+
+@frozen
+public struct _HStackLayout {
+    public var alignment: VerticalAlignment
+    public var spacing: CGFloat?
+
+    @inlinable
+    public init(alignment: VerticalAlignment = .center, spacing: CGFloat? = nil) {
+        self.alignment = alignment
+        self.spacing = spacing
+    }
+
+    public typealias AnimatableData = EmptyAnimatableData
+    public typealias Body = Swift.Never
+}
+
+@frozen
+public struct _VStackLayout {
+    public var alignment: HorizontalAlignment
+    public var spacing: CGFloat?
+
+    @inlinable
+    public init(alignment: HorizontalAlignment = .center, spacing: CGFloat? = nil) {
+        self.alignment = alignment
+        self.spacing = spacing
+    }
+
+    public typealias AnimatableData = EmptyAnimatableData
+    public typealias Body = Swift.Never
+}
+
+extension _HStackLayout: _VariadicView_ImplicitRoot {
+    static var implicitRoot: _HStackLayout { _HStackLayout() }
+}
+extension _VStackLayout: _VariadicView_ImplicitRoot {
+    static var implicitRoot: _VStackLayout { _VStackLayout() }
+}