Add ViewTrait and ViewTraitTests (#188)

Author: Kyle-Ye

Sources/OpenSwiftUICore/View/Trait/ViewTraitCollection.swift

@@ -0,0 +1,239 @@
+//
+//  ViewTrait.swift
+//  OpenSwiftUI
+//
+//  Audited for iOS 18.0
+//  Status: Blocked by ViewList
+//  ID: 9929B476764059557433A108298EE66F (SwiftUI)
+//  ID: 48526BA25CDCBF890FA91D018A5421B4 (SwiftUICore)
+
+import OpenGraphShims
+
+// MARK: - ViewTraitKey
+
+/// A type of key for a trait associated with the content of a
+/// container view.
+public protocol _ViewTraitKey {
+    /// The type of value produced by the trait.
+    associatedtype Value
+    
+    /// The default value of the trait.
+    static var defaultValue: Value { get }
+}
+
+// MARK: - _TraitWritingModifier [TODO]
+
+/// A view content adapter that associates a trait with its base content.
+@frozen
+public struct _TraitWritingModifier<Trait>: PrimitiveViewModifier where Trait : _ViewTraitKey {
+    public let value: Trait.Value
+
+    @inlinable
+    public init(value: Trait.Value) {
+        self.value = value
+    }
+
+    nonisolated public static func _makeView(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewInputs,
+        body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs
+    ) -> _ViewOutputs {
+        preconditionFailure("TODO")
+    }
+    nonisolated public static func _makeViewList(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewListInputs,
+        body: @escaping (_Graph, _ViewListInputs) -> _ViewListOutputs
+    ) -> _ViewListOutputs {
+        preconditionFailure("TODO")
+    }
+
+    nonisolated public static func _viewListCount(inputs: _ViewListCountInputs, body: (_ViewListCountInputs) -> Int?) -> Int? {
+        preconditionFailure("TODO")
+    }
+
+    private struct AddTrait {
+        @Attribute var modifier: _TraitWritingModifier
+        @OptionalAttribute var traits: ViewTraitCollection?
+    }
+}
+
+@available(*, unavailable)
+extension _TraitWritingModifier: Sendable {}
+
+extension View {
+    /// Associate a trait `value` for the given `key` for this view content.
+    @inlinable
+    nonisolated public func _trait<K>(_ key: K.Type, _ value: K.Value) -> some View where K: _ViewTraitKey {
+        return modifier(_TraitWritingModifier<K>(value: value))
+    }
+}
+
+// MARK: - _ConditionalTraitWritingModifier [TODO]
+
+/// Conditionally writes a trait.
+@frozen
+public struct _ConditionalTraitWritingModifier<Trait>: PrimitiveViewModifier where Trait : _ViewTraitKey {
+    public var value: Trait.Value
+    public var isEnabled: Bool
+    
+    @_alwaysEmitIntoClient
+    public init(traitKey: Trait.Type = Trait.self, value: Trait.Value, isEnabled: Bool) {
+        self.value = value
+        self.isEnabled = isEnabled
+    }
+     
+    nonisolated public static func _makeView(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewInputs,
+        body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs
+    ) -> _ViewOutputs {
+        preconditionFailure("TODO")
+    }
+    nonisolated public static func _makeViewList(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewListInputs,
+        body: @escaping (_Graph, _ViewListInputs) -> _ViewListOutputs
+    ) -> _ViewListOutputs {
+        preconditionFailure("TODO")
+    }
+
+    nonisolated public static func _viewListCount(inputs: _ViewListCountInputs, body: (_ViewListCountInputs) -> Int?) -> Int? {
+        preconditionFailure("TODO")
+    }
+}
+
+@available(*, unavailable)
+extension _ConditionalTraitWritingModifier: Sendable {}
+
+extension View {
+    @_alwaysEmitIntoClient
+    public func _trait<K>(_ key: K.Type = K.self, _ value: K.Value, isEnabled: Bool) -> some View where K: _ViewTraitKey {
+        modifier(_ConditionalTraitWritingModifier<K>(
+            value: value,
+            isEnabled: isEnabled
+        ))
+    }
+}
+
+// MARK: - TraitTransformerModifier [TODO]
+
+struct TraitTransformerModifier {
+    
+}
+
+extension View {
+    package func transformTrait<K>(_ key: K.Type = K.self, transform: @escaping (inout K.Value) -> Void) -> some View where K: _ViewTraitKey {
+        preconditionFailure("TODO")
+    }
+}
+
+// MARK: - ViewTraitCollection
+
+private protocol AnyViewTrait {
+    var id: ObjectIdentifier { get }
+    subscript<V>() -> V { get set }
+}
+
+package struct ViewTraitCollection {
+    package init() {
+        self.storage = []
+    }
+    
+    package func contains<Trait>(_ key: Trait.Type) -> Bool where Trait: _ViewTraitKey {
+        storage.contains { $0.id == ObjectIdentifier(key) }
+    }
+    
+    package func value<Trait>(for key: Trait.Type, defaultValue: Trait.Value) -> Trait.Value where Trait: _ViewTraitKey {
+        storage.first { $0.id == ObjectIdentifier(key) }?[] ?? defaultValue
+    }
+    
+    package func value<Trait>(for key: Trait.Type) -> Trait.Value where Trait: _ViewTraitKey {
+        value(for: key, defaultValue: key.defaultValue)
+    }
+        
+    package mutating func setValueIfUnset<Trait>(_ value: Trait.Value, for key: Trait.Type) where Trait: _ViewTraitKey {
+        guard !storage.contains(where: { $0.id == ObjectIdentifier(key) }) else {
+            return
+        }
+        storage.append(AnyTrait<Trait>(value: value))
+    }
+    
+    package subscript<Trait>(key: Trait.Type) -> Trait.Value where Trait : _ViewTraitKey {
+        get {
+            value(for: key)
+        }
+        set {
+            if let index = storage.firstIndex(where: { $0.id == ObjectIdentifier(key) }) {
+                storage[index][] = newValue
+            } else {
+                storage.append(AnyTrait<Trait>(value: newValue))
+            }
+        }
+    }
+    
+    package mutating func mergeValues(_ traits: ViewTraitCollection) {
+        for trait in traits.storage {
+            setErasedValue(trait: trait)
+        }
+    }
+    
+    private mutating func setErasedValue<ViewTrait>(trait: ViewTrait) where ViewTrait: AnyViewTrait {
+        if let index = storage.firstIndex(where: { $0.id == trait.id }) {
+            let value: Any = trait[]
+            storage[index][] = value
+        } else {
+            storage.append(trait)
+        }
+    }
+    
+    private var storage: [any AnyViewTrait]
+    
+    private struct AnyTrait<Trait>: AnyViewTrait where Trait: _ViewTraitKey {
+        typealias Value = Trait.Value
+        
+        var value: Value
+        
+        init(value: Trait.Value) {
+            self.value = value
+        }
+        
+        var id: ObjectIdentifier { ObjectIdentifier(Trait.self) }
+        
+        subscript<V>() -> V {
+            get { value as! V }
+            set { value = newValue as! Value }
+        }
+    }
+}
+
+// MARK: - ViewTraitKeys
+
+package struct ViewTraitKeys {
+    package var types: Set<ObjectIdentifier>
+    package var isDataDependent: Bool
+    
+    package init() {
+        types = []
+        isDataDependent = false
+    }
+    
+    package func contains<T>(_ type: T.Type) -> Bool where T: _ViewTraitKey{
+        types.contains(ObjectIdentifier(type))
+    }
+    
+    package mutating func insert<T>(_ type: T.Type) where T: _ViewTraitKey {
+        types.insert(ObjectIdentifier(type))
+    }
+    
+    package mutating func formUnion(_ other: ViewTraitKeys) {
+        types.formUnion(other.types)
+        isDataDependent = isDataDependent || other.isDataDependent
+    }
+
+    package func withDataDependent() -> ViewTraitKeys {
+        var copy = self
+        copy.isDataDependent = true
+        return copy
+    }
+}

Sources/OpenSwiftUICore/View/Trait/ViewTraitKey.swift

@@ -1,6 +1,6 @@
 //
 //  AnyViewTests.swift
-//  OpenSwiftUITests
+//  OpenSwiftUICoreTests
 
 @testable import OpenSwiftUICore
 import Testing