Kishikawa Katsumi
Dougさんは以下のマクロを実装するのは簡単だし読む場合も明らかと言ってるけどそこはだいぶ見解の相違がありそうだな。
public struct AddCompletionHandler: PeerDeclarationMacro { public static func expansion( of node: CustomAttributeSyntax, attachedTo declaration: DeclSyntax, in context: inout MacroExpansionContext ) throws -> [DeclSyntax] { // Only on functions at the moment. We could handle initializers as well // with a bit of work. guard let funcDecl = declaration.as(FunctionDeclSyntax.self) else { throw CustomError.message("@addCompletionHandler only works on functions") } // This only makes sense for async functions. if funcDecl.signature.asyncOrReasyncKeyword == nil { throw CustomError.message( "@addCompletionHandler requires an async function" ) } // Form the completion handler parameter. let resultType: TypeSyntax? = funcDecl.signature.output?.returnType.withoutTrivia() let completionHandlerParam = FunctionParameterSyntax( firstName: .identifier("completionHandler"), colon: .colonToken(trailingTrivia: .space), type: "(\(resultType ?? "")) -> Void" as TypeSyntax ) // Add the completion handler parameter to the parameter list. let parameterList = funcDecl.signature.input.parameterList let newParameterList: FunctionParameterListSyntax if let lastParam = parameterList.last { // We need to add a trailing comma to the preceding list. newParameterList = parameterList.removingLast() .appending( lastParam.withTrailingComma( .commaToken(trailingTrivia: .space) ) ) .appending(completionHandlerParam) } else { newParameterList = parameterList.appending(completionHandlerParam) } let callArguments: [String] = try parameterList.map { param in guard let argName = param.secondName ?? param.firstName else { throw CustomError.message( "@addCompletionHandler argument must have a name" ) } if let paramName = param.firstName, paramName.text != "_" { return "\(paramName.withoutTrivia()): \(argName.withoutTrivia())" } return "\(argName.withoutTrivia())" } let call: ExprSyntax = "\(funcDecl.identifier)(\(raw: callArguments.joined(separator: ", ")))" // FIXME: We should make CodeBlockSyntax ExpressibleByStringInterpolation, // so that the full body could go here. let newBody: ExprSyntax = """ Task { completionHandler(await \(call)) } """ // Drop the @addCompletionHandler attribute from the new declaration. let newAttributeList = AttributeListSyntax( funcDecl.attributes?.filter { guard case let .customAttribute(customAttr) = $0 else { return true } return customAttr != node } ?? [] ) let newFunc = funcDecl .withSignature( funcDecl.signature .withAsyncOrReasyncKeyword(nil) // drop async .withOutput(nil) // drop result type .withInput( // add completion handler parameter funcDecl.signature.input.withParameterList(newParameterList) .withoutTrailingTrivia() ) ) .withBody( CodeBlockSyntax( leftBrace: .leftBraceToken(leadingTrivia: .space), statements: CodeBlockItemListSyntax( [CodeBlockItemSyntax(item: .expr(newBody))] ), rightBrace: .rightBraceToken(leadingTrivia: .newline) ) ) .withAttributes(newAttributeList) .withLeadingTrivia(.newlines(2)) return [DeclSyntax(newFunc)] } }
Dougさん基準ｗ