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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2023 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 SwiftDiagnostics
import SwiftSyntax
import SwiftSyntaxBuilder
import SwiftSyntaxMacros
/// Provides default `fatalError` implementations for protocol methods.
///
/// This macro generates extensions that add default `fatalError` implementations
/// for each method in the protocol it is attached to.
public enum DefaultFatalErrorImplementationMacro: ExtensionMacro {
/// Unique identifier for messages related to this macro.
private static let messageID = MessageID(domain: "MacroExamples", id: "ProtocolDefaultImplementation")
/// Generates extension for the protocol to which this macro is attached.
public static func expansion(
of node: AttributeSyntax,
attachedTo declaration: some DeclGroupSyntax,
providingExtensionsOf type: some TypeSyntaxProtocol,
conformingTo protocols: [TypeSyntax],
in context: some MacroExpansionContext
) throws -> [ExtensionDeclSyntax] {
// Validate that the macro is being applied to a protocol declaration
guard let protocolDecl = declaration.as(ProtocolDeclSyntax.self) else {
throw SimpleDiagnosticMessage(
message: "Macro `defaultFatalErrorImplementation` can only be applied to a protocol",
diagnosticID: messageID,
severity: .error
)
}
// Extract all the methods from the protocol and assign default implementations
let methods = protocolDecl.memberBlock.members
.map(\.decl)
.compactMap { declaration -> FunctionDeclSyntax? in
guard var function = declaration.as(FunctionDeclSyntax.self) else {
return nil
}
function.body = CodeBlockSyntax {
ExprSyntax(#"fatalError("whoops 😅")"#)
}
return function
}
// Don't generate an extension if there are no methods
if methods.isEmpty {
return []
}
// Generate the extension containing the default implementations
let extensionDecl = ExtensionDeclSyntax(extendedType: type) {
for method in methods {
MemberBlockItemSyntax(decl: method)
}
}
return [extensionDecl]
}
}
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