Patch

Sources/StructTransaction/Source.swift

@@ -1,4 +1,7 @@
 
+/**
+ Available only for structs
+ */
 @attached(
   extension,
   conformances: DetectingType,
@@ -9,6 +12,13 @@
 )
 public macro Detecting() = #externalMacro(module: "StructTransactionMacros", type: "WriterMacro")
 
+/**
+ Available only for member functions.
+ Marker Macro that indicates if the function will be exported into Accessing struct.
+ */
+@attached(peer)
+public macro Exporting() = #externalMacro(module: "StructTransactionMacros", type: "MarkerMacro")
+
 /**
  Use ``Detecting()`` macro to adapt struct
  */

Sources/StructTransactionMacros/MarkerMacro.swift

@@ -0,0 +1,14 @@
+import SwiftCompilerPlugin
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import SwiftSyntaxMacros
+
+public struct MarkerMacro: Macro {
+
+}
+
+extension MarkerMacro: PeerMacro {
+  public static func expansion(of node: SwiftSyntax.AttributeSyntax, providingPeersOf declaration: some SwiftSyntax.DeclSyntaxProtocol, in context: some SwiftSyntaxMacros.MacroExpansionContext) throws -> [SwiftSyntax.DeclSyntax] {
+    []
+  }  
+}

Sources/StructTransactionMacros/Plugin.swift

@@ -6,6 +6,7 @@ import SwiftSyntaxMacros
 @main
 struct Plugin: CompilerPlugin {
   let providingMacros: [Macro.Type] = [
-    WriterMacro.self
+    WriterMacro.self,
+    MarkerMacro.self,
   ]
 }

Sources/StructTransactionMacros/WriterMacro.swift

@@ -67,6 +67,16 @@ extension WriterMacro: ExtensionMacro {
       return ""
     }
 
+    let functions = declaration
+      .memberBlock
+      .members
+      .compactMap {
+        $0.as(MemberBlockItemSyntax.self)?.decl.as(FunctionDeclSyntax.self)
+      }
+      .filter {
+        $0.attributes.contains { $0.trimmed.description == "@Exporting" }
+      }
+
     let c = PropertyCollector(viewMode: .all)
     c.onError = { node, error in
       context.addDiagnostics(from: error, node: node)
@@ -124,7 +134,13 @@ extension WriterMacro: ExtensionMacro {
           self.pointer = pointer
         }
 
+        // MARK: - Properties
+
         \(raw: decls.joined(separator: "\n\n"))
+
+        // MARK: - Functions
+
+        \(raw: functions.map(\.description).joined(separator: "\n\n"))
       }
       """ as DeclSyntax
 
@@ -162,6 +178,7 @@ extension WriterMacro: ExtensionMacro {
       }
 
       \(modifyingStructDecl)
+
       """ as CodeBlockItemListSyntax)
 
     return modifyingDecl

Tests/StructTransactionMacroTests/WriterMacroTests.swift

@@ -16,6 +16,94 @@ final class WriterMacroTests: XCTestCase {
     }
   }
 
+  func test_copying_functions() {
+
+    assertMacro {
+      """
+      @Detecting
+      struct MyState {
+        func hello() {
+        }
+
+        @Exporting
+        func hello2() {
+        }
+      }
+      """
+    } expansion: {
+      """
+      struct MyState {
+        func hello() {
+        }
+
+        @Exporting
+        func hello2() {
+        }
+      }
+
+      extension MyState: DetectingType {
+
+        // MARK: - Accessing
+        typealias AccessingTarget = Self
+
+        @discardableResult
+        public static func modify(source: inout Self, modifier: (inout Accessing) throws -> Void) rethrows -> AccessingResult {
+
+          try withUnsafeMutablePointer(to: &source) { pointer in
+            var modifying = Accessing(pointer: pointer)
+            try modifier(&modifying)
+            return AccessingResult(
+              readIdentifiers: modifying.$_readIdentifiers,
+              modifiedIdentifiers: modifying.$_modifiedIdentifiers
+            )
+          }
+        }
+
+        @discardableResult
+        public static func read(source: consuming Self, reader: (inout Accessing) throws -> Void) rethrows -> AccessingResult {
+
+          // TODO: check copying costs
+          var tmp = source
+
+          return try withUnsafeMutablePointer(to: &tmp) { pointer in
+            var modifying = Accessing(pointer: pointer)
+            try reader(&modifying)
+            return AccessingResult(
+              readIdentifiers: modifying.$_readIdentifiers,
+              modifiedIdentifiers: modifying.$_modifiedIdentifiers
+            )
+          }
+        }
+
+        public struct Accessing /* want to be ~Copyable */ {
+
+          public private (set) var $_readIdentifiers: Set<String> = .init()
+          public private (set) var $_modifiedIdentifiers: Set<String> = .init()
+
+          private let pointer: UnsafeMutablePointer<AccessingTarget>
+
+          init(pointer: UnsafeMutablePointer<AccessingTarget>) {
+            self.pointer = pointer
+          }
+
+          // MARK: - Properties
+
+
+
+          // MARK: - Functions
+
+
+
+          @Exporting
+          func hello2() {
+          }
+        }
+
+      }
+      """
+    }
+  }
+
   func test_() {
 
     assertMacro {

Tests/StructTransactionTests/MyState.swift

@@ -42,4 +42,9 @@ struct MyState {
     var name: String = ""
   }
 
+  @Exporting
+  mutating func updateName() {
+    self.name = "Hiroshi"
+  }
+
 }