Add an accessor macro example

Examples/Sources/MacroExamples/Implementation/Accessor/EnvironmentValueMacro.swift

@@ -0,0 +1,36 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import SwiftSyntax
+import SwiftSyntaxMacros
+
+public struct EnvironmentValueMacro: AccessorMacro {
+  public static func expansion(
+    of node: AttributeSyntax,
+    providingAccessorsOf declaration: some DeclSyntaxProtocol,
+    in context: some MacroExpansionContext
+  ) throws -> [AccessorDeclSyntax] {
+    guard
+      case let .argumentList(arguments) = node.arguments,
+      let argument = arguments.first
+    else { return [] }
+
+    return [
+      """
+      get { self[\(argument.expression)] }
+      """,
+      """
+      set { self[\(argument.expression)] = newValue }
+      """,
+    ]
+  }
+}

Examples/Sources/MacroExamples/Implementation/Plugin.swift

@@ -26,6 +26,7 @@ struct MyPlugin: CompilerPlugin {
     DefaultFatalErrorImplementationMacro.self,
     DictionaryStorageMacro.self,
     DictionaryStoragePropertyMacro.self,
+    EnvironmentValueMacro.self,
     EquatableExtensionMacro.self,
     FontLiteralMacro.self,
     FuncUniqueMacro.self,

Examples/Sources/MacroExamples/Interface/AccessorMacros.swift

@@ -0,0 +1,24 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#if canImport(SwiftUI)
+
+import SwiftUI
+
+// MARK: - EnvironmentValue Accessor
+
+/// Adds getter / setter to an attached environment value with specified EnvironmentKey
+@attached(accessor)
+public macro EnvironmentValue(for key: any EnvironmentKey.Type) =
+  #externalMacro(module: "MacroExamplesImplementation", type: "EnvironmentValueMacro")
+
+#endif

Examples/Sources/MacroExamples/Playground/AccessorMacrosPlayground.swift

@@ -0,0 +1,37 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+// MARK: - EnvironmentValue Accessor
+
+import MacroExamplesInterface
+
+#if canImport(SwiftUI)
+
+import SwiftUI
+
+private struct MyEnvironmentKey: EnvironmentKey {
+  static let defaultValue: String = "Default value"
+}
+
+extension EnvironmentValues {
+  @EnvironmentValue(for: MyEnvironmentKey.self)
+  var myCustomValue: String
+}
+
+func runEnvironmentValueAccessorMacroPlayground() {
+  var environmentValues = EnvironmentValues()
+  print("Default myCustomValue: \(environmentValues.myCustomValue)")
+  environmentValues.myCustomValue = "New value"
+  print("New myCustomValue: \(environmentValues.myCustomValue)")
+}
+
+#endif

Examples/Sources/MacroExamples/Playground/main.swift

@@ -47,3 +47,11 @@ runMemberMacrosPlayground()
 // MARK: - Peer Macros
 
 runPeerMacrosPlayground()
+
+// MARK: - Accessor Macros
+
+#if canImport(SwiftUI)
+
+runEnvironmentValueAccessorMacroPlayground()
+
+#endif

Examples/Tests/MacroExamples/Implementation/Accessor/EnvironmentValueMacroTests.swift

@@ -0,0 +1,44 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import MacroExamplesImplementation
+import SwiftSyntaxMacros
+import SwiftSyntaxMacrosTestSupport
+import XCTest
+
+final class EnvironmentValueMacroMacroTests: XCTestCase {
+  private let macros = ["EnvironmentValue": EnvironmentValueMacro.self]
+
+  func testEnvironmentValue() {
+    assertMacroExpansion(
+      """
+      extension EnvironmentValues {
+          @EnvironmentValue(for: MyEnvironmentKey.self)
+          var myCustomValue: String
+      }
+      """,
+      expandedSource: """
+        extension EnvironmentValues {
+            var myCustomValue: String {
+                get {
+                    self[MyEnvironmentKey.self]
+                }
+                set {
+                    self[MyEnvironmentKey.self] = newValue
+                }
+            }
+        }
+        """,
+      macros: macros
+    )
+  }
+}