[MacroSystem] Expand extension macros.

Author: hborla

Sources/SwiftSyntaxMacros/MacroSystem.swift

@@ -115,7 +115,8 @@ class MacroApplication<Context: MacroExpansionContext>: SyntaxRewriter {
  || macro is MemberMacro.Type
  || macro is AccessorMacro.Type
  || macro is MemberAttributeMacro.Type
- || macro is ConformanceMacro.Type)
+ || macro is ConformanceMacro.Type
+ || macro is ExtensionMacro.Type)
  }
 
  if newAttributes.isEmpty {
@@ -438,6 +439,20 @@ extension MacroApplication {
  }
  }
 
+ let extensionMacroAttrs = getMacroAttributes(attachedTo: decl.as(DeclSyntax.self)!, ofType: ExtensionMacro.Type.self)
+ let extendedTypeSyntax = TypeSyntax("\(extendedType.trimmed)")
+ for (attribute, extensionMacro) in extensionMacroAttrs {
+ do {
+ let newExtensions = try extensionMacro.expansion(of: attribute,
+ attachedTo: decl,
+ providingExtensionsOf: extendedTypeSyntax,
+ in: context)
+ extensions.append(contentsOf: newExtensions.map(DeclSyntax.init))
+ } catch {
+ context.addDiagnostics(from: error, node: attribute)
+ }
+ }
+
  return extensions
  }
 

Tests/SwiftSyntaxMacrosTest/MacroSystemTests.swift

@@ -682,6 +682,26 @@ public struct SendableConformanceMacro: ConformanceMacro {
  }
 }
 
+public struct SendableExtensionMacro: ExtensionMacro {
+ public static func expansion(
+ of node: AttributeSyntax,
+ attachedTo: some DeclGroupSyntax,
+ providingExtensionsOf type: some TypeSyntaxProtocol,
+ in context: some MacroExpansionContext
+ ) throws -> [ExtensionDeclSyntax] {
+ let sendableExtension: DeclSyntax =
+ """
+ extension \(type.trimmed): Sendable {}
+ """
+
+ guard let extensionDecl = sendableExtension.as(ExtensionDeclSyntax.self) else {
+ return []
+ }
+
+ return [extensionDecl]
+ }
+}
+
 public struct DeclsFromStringsMacroNoAttrs: DeclarationMacro {
  public static var propagateFreestandingMacroAttributes: Bool { false }
  public static var propagateFreestandingMacroModifiers: Bool { false }
@@ -726,6 +746,7 @@ public let testMacros: [String: Macro.Type] = [
  "customTypeWrapper": CustomTypeWrapperMacro.self,
  "unwrap": UnwrapMacro.self,
  "AddSendable": SendableConformanceMacro.self,
+ "AddSendableExtension": SendableExtensionMacro.self,
 ]
 
 final class MacroSystemTests: XCTestCase {
@@ -1196,4 +1217,23 @@ final class MacroSystemTests: XCTestCase {
  indentationWidth: indentationWidth
  )
  }
+
+ func testExtensionExpansion() {
+ assertMacroExpansion(
+ """
+ @AddSendableExtension
+ struct MyType {
+ }
+ """,
+ expandedSource: """
+
+ struct MyType {
+ }
+ extension MyType: Sendable {
+ }
+ """,
+ macros: testMacros,
+ indentationWidth: indentationWidth
+ )
+ }
 }