OpenSwiftUIProject · Kyle-Ye · Sep 7, 2025 · Sep 7, 2025 · Sep 7, 2025
diff --git a/Sources/OpenSwiftUICore/Modifier/CustomViewModifier.swift b/Sources/OpenSwiftUICore/Modifier/CustomViewModifier.swift
@@ -161,13 +161,11 @@ extension ViewModifier {
         inputs: inout _GraphInputs,
         fields: DynamicPropertyCache.Fields
     ) -> (_GraphValue<Body>, _DynamicPropertyBuffer?) {
-        let kind = Metadata(Self.self).kind
-        switch kind {
-        case .struct, .enum, .optional, .tuple:
-            return ModifierBodyAccessor().makeBody(container: modifier, inputs: &inputs, fields: fields)
-        default:
+        guard Metadata(Self.self).isValueType else {
             preconditionFailure("view modifiers must be value types: \(Self.self)")
         }
+        let accessor = ModifierBodyAccessor<Self>()
+        return accessor.makeBody(container: modifier, inputs: &inputs, fields: fields)
     }
 }
 

diff --git a/Sources/OpenSwiftUICore/Modifier/ViewModifier/EnvironmentalModifier.swift b/Sources/OpenSwiftUICore/Modifier/ViewModifier/EnvironmentalModifier.swift
@@ -0,0 +1,143 @@
+//
+//  EnvironmentalModifier.swift
+//  OpenSwiftUICore
+//
+//  Audited for 6.5.4
+//  Status: Complete
+//  ID: A1B6966B83442495FADFE75F475ECBE2 (SwiftUICore)
+
+import OpenAttributeGraphShims
+
+// MARK: - EnvironmentalModifier
+
+/// A modifier that must resolve to a concrete modifier in an environment before
+/// use.
+@available(OpenSwiftUI_v1_0, *)
+public protocol EnvironmentalModifier: ViewModifier where Body == Never {
+    /// The type of modifier to use after being resolved.
+    associatedtype ResolvedModifier: ViewModifier
+
+    /// Resolve to a concrete modifier in the given `environment`.
+    func resolve(in environment: EnvironmentValues) -> ResolvedModifier
+
+    @available(OpenSwiftUI_v3_0, *)
+    static var _requiresMainThread: Bool { get }
+
+    @available(OpenSwiftUI_v5_0, *)
+    static var _tracksEnvironmentDependencies: Bool { get }
+}
+
+// MARK: - EnvironmentalModifier Default Implementations
+
+@available(OpenSwiftUI_v1_0, *)
+extension EnvironmentalModifier {
+    nonisolated public static func _makeView(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewInputs,
+        body: @escaping (_Graph, _ViewInputs) -> _ViewOutputs
+    ) -> _ViewOutputs {
+        var inputs = inputs
+        let fields = DynamicPropertyCache.fields(of: Self.self)
+        let (resolvedModifier, buffer) = makeResolvedModifier(modifier: modifier, inputs: &inputs.base, fields: fields)
+        let outputs = ResolvedModifier.makeDebuggableView(
+            modifier: resolvedModifier,
+            inputs: inputs,
+            body: body
+        )
+        if let buffer {
+            buffer.traceMountedProperties(to: modifier, fields: fields)
+        }
+        return outputs
+    }
+
+    nonisolated public static func _makeViewList(
+        modifier: _GraphValue<Self>,
+        inputs: _ViewListInputs,
+        body: @escaping (_Graph, _ViewListInputs) -> _ViewListOutputs
+    ) -> _ViewListOutputs {
+        var inputs = inputs
+        let fields = DynamicPropertyCache.fields(of: Self.self)
+        let (resolvedModifier, buffer) = makeResolvedModifier(modifier: modifier, inputs: &inputs.base, fields: fields)
+        let outputs = ResolvedModifier.makeDebuggableViewList(
+            modifier: resolvedModifier,
+            inputs: inputs,
+            body: body
+        )
+        if let buffer {
+            buffer.traceMountedProperties(to: modifier, fields: fields)
+        }
+        return outputs
+    }
+
+    nonisolated private static func makeResolvedModifier(
+        modifier: _GraphValue<Self>,
+        inputs: inout _GraphInputs,
+        fields: DynamicPropertyCache.Fields
+    ) -> (_GraphValue<ResolvedModifier>, _DynamicPropertyBuffer?) {
+        guard Metadata(Self.self).isValueType else {
+            preconditionFailure("Environmental modifiers must be value types: \(Self.self)")
+        }
+        var fields = fields
+        if !fields.behaviors.contains(.requiresMainThread), !_requiresMainThread {
+            fields.behaviors.formUnion(
+                !fields.behaviors.contains(.allowsAsync) && isLinkedOnOrAfter(.v4) ? .allowsAsync : []
+            )
+        }
+        let accessor = EnvironmentalBodyAccessor<Self>(
+            environment: inputs.environment,
+            tracksDependencies: _tracksEnvironmentDependencies
+        )
+        return accessor.makeBody(container: modifier, inputs: &inputs, fields: fields)
+    }
+
+    @available(OpenSwiftUI_v3_0, *)
+    public static var _requiresMainThread: Bool {
+        true
+    }
+
+    @available(OpenSwiftUI_v5_0, *)
+    public static var _tracksEnvironmentDependencies: Bool {
+        true
+    }
+}
+
+// MARK: - EnvironmentalBodyAccessor
+
+private struct EnvironmentalBodyAccessor<V>: BodyAccessor where V: EnvironmentalModifier {
+    typealias Container = V
+
+    typealias Body = V.ResolvedModifier
+
+    @Attribute
+    var environment: EnvironmentValues
+    let tracker: PropertyList.Tracker
+    let tracksDependencies: Bool
+
+    init(
+        environment: Attribute<EnvironmentValues>,
+        tracksDependencies: Bool
+    ) {
+        self._environment = environment
+        self.tracker = .init()
+        self.tracksDependencies = tracksDependencies
+    }
+
+    func updateBody(of container: V, changed: Bool) {
+        let (environment, environmentChanged) = $environment.changedValue()
+        guard changed ||
+            (
+                environmentChanged && (
+                    !tracksDependencies ||
+                    tracker.hasDifferentUsedValues(environment.plist)
+                )
+            )
+        else {
+            return
+        }
+        tracker.reset()
+        let newEnvironment = EnvironmentValues(environment.plist, tracker: tracker)
+        setBody {
+            container.resolve(in: newEnvironment)
+        }
+    }
+}
diff --git a/Sources/OpenSwiftUICore/View/CustomView.swift b/Sources/OpenSwiftUICore/View/CustomView.swift
@@ -51,14 +51,11 @@ extension View {
         inputs: inout _GraphInputs,
         fields: DynamicPropertyCache.Fields
     ) -> (_GraphValue<Body>, _DynamicPropertyBuffer?) {
-        let kind = Metadata(Self.self).kind
-        switch kind {
-        case .struct, .enum, .optional, .tuple:
-            let accessor = ViewBodyAccessor<Self>()
-            return accessor.makeBody(container: view, inputs: &inputs, fields: fields)
-        default:
+        guard Metadata(Self.self).isValueType else {
             preconditionFailure("views must be value types (either a struct or an enum); \(Self.self) is a class.")
         }
+        let accessor = ViewBodyAccessor<Self>()
+        return accessor.makeBody(container: view, inputs: &inputs, fields: fields)
     }
 }
 

diff --git a/Sources/OpenSwiftUICore/View/VariadicView.swift b/Sources/OpenSwiftUICore/View/VariadicView.swift
@@ -348,14 +348,11 @@ extension _VariadicView.ViewRoot {
         inputs: inout _GraphInputs,
         fields: DynamicPropertyCache.Fields
     ) -> (_GraphValue<Body>, _DynamicPropertyBuffer?) {
-        let kind = Metadata(Self.self).kind
-        switch kind {
-        case .struct, .enum, .optional, .tuple:
-            let accessor = ViewRootBodyAccessor<Self>(list: list, contentSubgraph: .current!)
-            return accessor.makeBody(container: root, inputs: &inputs, fields: fields)
-        default:
+        guard Metadata(Self.self).isValueType else {
             preconditionFailure("views root must be value types (either a struct or an enum); \(Self.self) is a class.")
         }
+        let accessor = ViewRootBodyAccessor<Self>(list: list, contentSubgraph: .current!)
+        return accessor.makeBody(container: root, inputs: &inputs, fields: fields)
     }
 }