Add Transition API

Sources/OpenSwiftUICore/Animation/Transition/AnyTransition.swift

@@ -0,0 +1,109 @@
+//
+//  AnyTransition.swift
+//  OpenSwiftUICore
+//
+//  Audited for 6.5.4
+//  Status: Complete
+//  ID: 142ABD4E569D763299C4081019352BCD (SwiftUICore)
+
+/// A type-erased transition.
+///
+/// - See Also: `Transition`
+@available(OpenSwiftUI_v1_0, *)
+@frozen
+public struct AnyTransition {
+    fileprivate let box: AnyTransitionBox
+
+    /// Create an instance that type-erases `transition`.
+    @available(OpenSwiftUI_v5_0, *)
+    public init<T>(_ transition: T) where T: Transition {
+        self.box = TransitionBox(transition)
+    }
+
+    package func visitBase<V>(applying v: inout V) where V: TransitionVisitor {
+        box.visitBase(applying: &v)
+    }
+
+    package func visitType<V>(applying v: inout V) where V: TransitionTypeVisitor {
+        box.visitType(applying: &v)
+    }
+
+    package func base<T>(as _: T.Type) -> T? where T: Transition {
+        guard let box = box as? TransitionBox<T> else {
+            return nil
+        }
+        return box.base
+    }
+
+    package var isIdentity: Bool {
+        box.isIdentity
+    }
+
+    package func adjustedForAccessibility(prefersCrossFade: Bool) -> AnyTransition {
+        guard box.hasMotion, prefersCrossFade else {
+            return self
+        }
+        return .opacity
+    }
+}
+
+@available(*, unavailable)
+extension AnyTransition: Sendable {}
+
+package protocol TransitionVisitor {
+    mutating func visit<T>(_ transition: T) where T: Transition
+}
+
+package protocol TransitionTypeVisitor {
+    mutating func visit<T>(_ type: T.Type) where T: Transition
+}
+
+@available(OpenSwiftUI_v1_0, *)
+@usableFromInline
+class AnyTransitionBox {
+    init() {}
+
+    func visitBase<V>(applying v: inout V) where V: TransitionVisitor {
+        _openSwiftUIBaseClassAbstractMethod()
+    }
+
+    func visitType<V>(applying v: inout V) where V: TransitionTypeVisitor {
+        _openSwiftUIBaseClassAbstractMethod()
+    }
+
+    var isIdentity: Bool {
+        _openSwiftUIBaseClassAbstractMethod()
+    }
+
+    var hasMotion: Bool {
+        _openSwiftUIBaseClassAbstractMethod()
+    }
+}
+
+@available(*, unavailable)
+extension AnyTransitionBox: Sendable {}
+
+@available(OpenSwiftUI_v5_0, *)
+private final class TransitionBox<T>: AnyTransitionBox where T: Transition {
+    let base: T
+
+    init(_ base: T) {
+        self.base = base
+    }
+
+    override func visitBase<V>(applying v: inout V) where V: TransitionVisitor {
+        v.visit(base)
+    }
+
+    override func visitType<V>(applying v: inout V) where V: TransitionTypeVisitor {
+        v.visit(T.self)
+    }
+
+    override var isIdentity: Bool {
+        T.Body.self == PlaceholderContentView<T>.self
+    }
+
+    override var hasMotion: Bool {
+        T.properties.hasMotion
+    }
+}

Sources/OpenSwiftUICore/Animation/Transition/ContentTransition.swift

@@ -0,0 +1,79 @@
+//
+//  ContentTransition.swift
+//  OpenSwiftUICore
+
+// TODO
+
+@available(OpenSwiftUI_v4_0, *)
+public struct ContentTransition: Equatable, Sendable {
+    package enum Storage: Equatable, @unchecked Sendable {
+        case named(ContentTransition.NamedTransition)
+//        case custom(ContentTransition.CustomTransition)
+//        case symbolReplace(_SymbolEffect.ReplaceConfiguration)
+    }
+
+    @_spi(Private)
+    public struct Style: Hashable, Sendable/*, Codable*/ {
+        package enum Storage: Hashable, Sendable {
+            case `default`
+
+            case sessionWidget
+
+            case animatedWidget
+        }
+
+        package var storage: ContentTransition.Style.Storage
+
+        package init(_ storage: ContentTransition.Style.Storage) {
+            self.storage = storage
+        }
+
+        public static let `default`: ContentTransition.Style = .init(.default)
+
+        public static let sessionWidget: ContentTransition.Style = .init(.sessionWidget)
+
+        @available(OpenSwiftUI_v5_0, *)
+        public static let animatedWidget: ContentTransition.Style = .init(.animatedWidget)
+    }
+
+    package var storage: ContentTransition.Storage
+
+    package var isReplaceable: Bool
+
+    package init(storage: ContentTransition.Storage) {
+        _openSwiftUIUnimplementedFailure()
+    }
+
+    package struct NamedTransition: Hashable, Sendable {
+        package enum Name: Hashable {
+            case `default`
+            case identity
+            case opacity
+            case diff
+            case fadeIfDifferent
+            case text(different: Bool)
+            // case numericText(ContentTransition.NumericTextConfiguration)
+        }
+
+        package var name: ContentTransition.NamedTransition.Name
+        package var layoutDirection: LayoutDirection?
+        package var style: ContentTransition.Style?
+
+        package init(
+            name: ContentTransition.NamedTransition.Name = .default,
+            layoutDirection: LayoutDirection? = nil,
+            style: ContentTransition.Style? = nil
+        ) {
+            self.name = name
+            self.layoutDirection = layoutDirection
+            self.style = style
+        }
+    }
+
+    // TODO: NumericTextConfiguration
+
+    // TODO
+    package enum Effect {}
+
+    package enum State {}
+}