Update Environment implementation (#648)

Author: Kyle-Ye

Sources/OpenSwiftUICore/Data/Environment/Environment.swift

@@ -1,10 +1,11 @@
 //
 //  Environment.swift
-//  OpenSwiftUI
+//  OpenSwiftUICore
 //
-//  Audited for 3.5.2
+//  Audited for 6.5.4
 //  Status: Complete
-//  ID: 7B48F30970137591804EEB8D0D309152
+//  ID: 7B48F30970137591804EEB8D0D309152 (SwiftUI)
+//  ID: 24E0E088473ED74681D096110CC5FC9A (SwiftUICore)
 
 import OpenAttributeGraphShims
 #if OPENSWIFTUI_SWIFT_LOG
@@ -13,6 +14,8 @@ public import Logging
 public import os
 #endif
 
+// MARK: - Environment
+
 /// A property wrapper that reads a value from a view's environment.
 ///
 /// Use the `Environment` property wrapper to read a value
@@ -46,7 +49,7 @@ public import os
 ///
 /// For the complete list of environment values provided by OpenSwiftUI, see the
 /// properties of the ``EnvironmentValues`` structure. For information about
-/// creating custom environment values, see the ``EnvironmentKey`` protocol.
+/// creating custom environment values, see the ``Entry()`` macro.
 ///
 /// ### Get an observable object
 ///
@@ -57,7 +60,7 @@ public import os
 /// the object itself or a key path.
 ///
 /// To set the object in the environment using the object itself, use the
-/// ``View/environment(_:)-4516h`` modifier:
+/// ``View/environment(_:)`` modifier:
 ///
 ///     @Observable
 ///     class Library {
@@ -94,7 +97,7 @@ public import os
 /// By default, reading an object from the environment returns a non-optional
 /// object when using the object type as the key. This default behavior assumes
 /// that a view in the current hierarchy previously stored a non-optional
-/// instance of the type using the ``View/environment(_:)-4516h`` modifier. If
+/// instance of the type using the ``View/environment(_:)`` modifier. If
 /// a view attempts to retrieve an object using its type and that object isn't
 /// in the environment, OpenSwiftUI throws an exception.
 ///
@@ -141,18 +144,25 @@ public import os
 ///         }
 ///     }
 ///
+@available(OpenSwiftUI_v1_0, *)
 @frozen
 @propertyWrapper
 public struct Environment<Value>: DynamicProperty {
+
     @usableFromInline
     @frozen
-    enum Content {
+    internal enum Content: @unchecked Sendable {
+
+        /// A key path describing how to dereference the view's current
+        /// environment to produce the linked value.
         case keyPath(KeyPath<EnvironmentValues, Value>)
+
+        /// The view's current value of the environment property.
         case value(Value)
     }
 
     @usableFromInline
-    var content: Content
+    internal var content: Content
 
     /// Creates an environment property to read the specified key path.
     ///
@@ -194,7 +204,6 @@ public struct Environment<Value>: DynamicProperty {
     ///         }
     ///     }
     ///
-    // Audited for RELEASE_2023
     @inlinable
     public var wrappedValue: Value {
         switch content {
@@ -231,7 +240,7 @@ public struct Environment<Value>: DynamicProperty {
     }
 
     @usableFromInline
-    func error() -> Never {
+    internal func error() -> Never {
         preconditionFailure("Reading Environment<\(Value.self)> outside View.body")
     }
 
@@ -241,52 +250,96 @@ public struct Environment<Value>: DynamicProperty {
         fieldOffset: Int,
         inputs: inout _GraphInputs
     ) {
-        buffer.append(
-            EnvironmentBox<Value>(
-                environment: inputs.environment
-            ),
-            fieldOffset: fieldOffset
-        )
+        if Value.self == EnvironmentValues.self {
+            buffer.append(
+                FullEnvironmentBox(environment: inputs.environment),
+                fieldOffset: fieldOffset
+            )
+        } else {
+            buffer.append(
+                EnvironmentBox<Value>(environment: inputs.environment),
+                fieldOffset: fieldOffset
+            )
+        }
     }
 }
 
 @available(OpenSwiftUI_v1_0, *)
 extension Environment: Sendable where Value: Sendable {}
 
-private struct EnvironmentBox<Value>: DynamicPropertyBox {
+// MARK: - FullEnvironmentBox
+
+private struct FullEnvironmentBox: DynamicPropertyBox {
     @Attribute var environment: EnvironmentValues
-    var keyPath: KeyPath<EnvironmentValues, Value>?
-    var value: Value?
-    
-    init(environment: Attribute<EnvironmentValues>) {
-        _environment = environment
-        keyPath = nil
-        value = nil
-    }
-        
-    func destroy() {}
-    func reset() {}
-    mutating func update(property: inout Environment<Value>, phase _: _GraphInputs.Phase) -> Bool {
+    var keyPath: KeyPath<EnvironmentValues, EnvironmentValues>?
+    var value: EnvironmentValues?
+    var tracker: PropertyList.Tracker = .init()
+
+    typealias Property = Environment<EnvironmentValues>
+
+    mutating func update(property: inout Property, phase _: ViewPhase) -> Bool {
         guard case let .keyPath(propertyKeyPath) = property.content else {
             return false
         }
-        let (environment, environmentChanged) = _environment.changedValue()
+        let (environment, environmentChanged) = $environment.changedValue()
         let keyPathChanged = (propertyKeyPath != keyPath)
-        if keyPathChanged { keyPath = propertyKeyPath }
+        if keyPathChanged {
+            keyPath = propertyKeyPath
+        }
         let valueChanged: Bool
         if keyPathChanged || environmentChanged {
             let newValue = environment[keyPath: propertyKeyPath]
+            if let value, !tracker.hasDifferentUsedValues(environment.plist) {
+                valueChanged = false
+            } else {
+                tracker.reset()
+                tracker.initializeValues(from: newValue.plist)
+                value = EnvironmentValues(newValue.plist, tracker: tracker)
+                valueChanged = true
+            }
+        } else {
+            valueChanged = false
+        }
+        property.content = .value(value!)
+        return valueChanged
+    }
+}
+
+// MARK: - EnvironmentBox
+
+private struct EnvironmentBox<Value>: DynamicPropertyBox {
+    @Attribute var environment: EnvironmentValues
+    var keyPath: KeyPath<EnvironmentValues, Value>?
+    var value: Value?
+    var hadObservation: Bool = false
+
+    typealias Property = Environment<Value>
+
+    mutating func update(property: inout Property, phase _: ViewPhase) -> Bool {
+        guard case let .keyPath(propertyKeyPath) = property.content else {
+            return false
+        }
+        let (environment, environmentChanged) = $environment.changedValue()
+        let keyPathChanged = (propertyKeyPath != keyPath)
+        var valueChanged = environmentChanged
+        if keyPathChanged {
+            keyPath = propertyKeyPath
+            valueChanged = true
+        }
+        if keyPathChanged || environmentChanged || hadObservation {
+            let (newValue, accessList) = _withObservation {
+                environment[keyPath: propertyKeyPath]
+            }
+            hadObservation = accessList != nil
             if let value, compareValues(value, newValue) {
                 valueChanged = false
             } else {
                 value = newValue
-                valueChanged = true
             }
         } else {
             valueChanged = false
         }
-        let value: Value = self.value!
-        property.content = .value(value)
+        property.content = .value(value!)
         return valueChanged
     }
 }