Add 'Generate enum associated value accessors' code action

Sources/SwiftSyntaxCodeActions/CMakeLists.txt

@@ -6,6 +6,7 @@ add_library(SwiftSyntaxCodeActions STATIC
   ConvertIntegerLiteral.swift
   ConvertJSONToCodableStruct.swift
   ConvertStringConcatenationToStringInterpolation.swift
+  GenerateEnumCaseAccessors.swift
   IndentationRemover.swift
   PackageManifestEdits.swift
   SyntaxCodeActionProvider.swift

Sources/SwiftSyntaxCodeActions/GenerateEnumCaseAccessors.swift

@@ -0,0 +1,199 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2026 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 SwiftBasicFormat
+import SwiftExtensions
+import SwiftRefactor
+import SwiftSyntax
+
+/// Syntactic code action that adds an `as<Case>` computed property for every
+/// enum case with associated values, returning the value(s) as an optional.
+struct GenerateEnumCaseAsAccessors: SyntaxRefactoringCodeActionProvider {
+  static let title: String = "Generate 'as' accessors for enum cases"
+
+  static func nodeToRefactor(in scope: SyntaxCodeActionScope) -> EnumDeclSyntax? {
+    return scope.innermostNodeContainingRange?.findParentOfSelf(
+      ofType: EnumDeclSyntax.self,
+      stoppingIf: { $0.is(CodeBlockSyntax.self) }
+    )
+  }
+
+  static func textRefactor(syntax: EnumDeclSyntax, in context: Void) throws -> [SourceEdit] {
+    let indentation = accessorIndentation(for: syntax)
+    let existingNames = existingMemberNames(of: syntax)
+
+    var accessors: [String] = []
+    for element in enumCaseElements(of: syntax) {
+      guard let parameters = element.parameterClause?.parameters, !parameters.isEmpty else {
+        continue
+      }
+      let name = "as\(capitalizedCaseName(of: element))"
+      guard !existingNames.contains(name) else { continue }
+      accessors.append(
+        makeAsAccessor(
+          name: name,
+          casePattern: element.name.text,
+          parameters: parameters,
+          baseIndentation: indentation.base,
+          indentationStep: indentation.step
+        )
+      )
+    }
+
+    return try sourceEdits(insertingAccessors: accessors, into: syntax)
+  }
+
+  private static func makeAsAccessor(
+    name: String,
+    casePattern: String,
+    parameters: EnumCaseParameterListSyntax,
+    baseIndentation: Trivia,
+    indentationStep: Trivia
+  ) -> String {
+    let memberIndentation = (baseIndentation + indentationStep).description
+    let bodyIndentation = (baseIndentation + indentationStep + indentationStep).description
+    let bindings = parameters.enumerated().map { index, parameter -> String in
+      if let label = parameter.firstName, label.text != "_" {
+        return label.text
+      }
+      return parameters.count == 1 ? "value" : "value\(index + 1)"
+    }
+    let returnType: String
+    if let parameter = parameters.only {
+      let type = parameter.type.trimmedDescription
+      returnType = needsParenthesesBeforeOptional(parameter.type) ? "(\(type))?" : "\(type)?"
+    } else {
+      let elements = parameters.map { parameter -> String in
+        if let label = parameter.firstName, label.text != "_" {
+          return "\(label.text): \(parameter.type.trimmedDescription)"
+        }
+        return parameter.type.trimmedDescription
+      }
+      returnType = "(\(elements.joined(separator: ", ")))?"
+    }
+    let boundValues = bindings.joined(separator: ", ")
+    let returnValue = bindings.only ?? "(\(boundValues))"
+    return """
+      \(memberIndentation)var \(name): \(returnType) {
+      \(bodyIndentation)if case let .\(casePattern)(\(boundValues)) = self { return \(returnValue) }
+      \(bodyIndentation)return nil
+      \(memberIndentation)}
+      """
+  }
+}
+
+/// Syntactic code action that adds an `is<Case>` Boolean computed property for
+/// every enum case.
+struct GenerateEnumCaseIsAccessors: SyntaxRefactoringCodeActionProvider {
+  static let title: String = "Generate 'is' accessors for enum cases"
+
+  static func nodeToRefactor(in scope: SyntaxCodeActionScope) -> EnumDeclSyntax? {
+    return scope.innermostNodeContainingRange?.findParentOfSelf(
+      ofType: EnumDeclSyntax.self,
+      stoppingIf: { $0.is(CodeBlockSyntax.self) }
+    )
+  }
+
+  static func textRefactor(syntax: EnumDeclSyntax, in context: Void) throws -> [SourceEdit] {
+    let indentation = accessorIndentation(for: syntax)
+    let existingNames = existingMemberNames(of: syntax)
+
+    let accessors = enumCaseElements(of: syntax).compactMap { element -> String? in
+      let name = "is\(capitalizedCaseName(of: element))"
+      guard !existingNames.contains(name) else { return nil }
+      return makeIsAccessor(
+        name: name,
+        casePattern: element.name.text,
+        baseIndentation: indentation.base,
+        indentationStep: indentation.step
+      )
+    }
+
+    return try sourceEdits(insertingAccessors: accessors, into: syntax)
+  }
+
+  private static func makeIsAccessor(
+    name: String,
+    casePattern: String,
+    baseIndentation: Trivia,
+    indentationStep: Trivia
+  ) -> String {
+    let memberIndentation = (baseIndentation + indentationStep).description
+    let bodyIndentation = (baseIndentation + indentationStep + indentationStep).description
+    return """
+      \(memberIndentation)var \(name): Bool {
+      \(bodyIndentation)if case .\(casePattern) = self { return true }
+      \(bodyIndentation)return false
+      \(memberIndentation)}
+      """
+  }
+}
+
+// MARK: - Shared helpers
+
+private func enumCaseElements(of enumDecl: EnumDeclSyntax) -> [EnumCaseElementSyntax] {
+  enumDecl.memberBlock.members.flatMap { member -> [EnumCaseElementSyntax] in
+    guard let caseDecl = member.decl.as(EnumCaseDeclSyntax.self) else { return [] }
+    return Array(caseDecl.elements)
+  }
+}
+
+/// The names of the enum's existing properties, so an accessor whose name is already taken isn't generated again.
+private func existingMemberNames(of enumDecl: EnumDeclSyntax) -> Set<String> {
+  var names: Set<String> = []
+  for member in enumDecl.memberBlock.members {
+    guard let variable = member.decl.as(VariableDeclSyntax.self) else { continue }
+    for binding in variable.bindings {
+      if let pattern = binding.pattern.as(IdentifierPatternSyntax.self) {
+        names.insert(pattern.identifier.identifier?.name ?? pattern.identifier.text)
+      }
+    }
+  }
+  return names
+}
+
+/// The `as`/`is` accessor name for a case, with the leading character upper-cased.
+private func capitalizedCaseName(of element: EnumCaseElementSyntax) -> String {
+  let caseName = element.name.identifier?.name ?? element.name.text
+  return caseName.prefix(1).uppercased() + caseName.dropFirst()
+}
+
+/// Whether `type` must be parenthesized to be made optional. Types that the postfix `?` already
+/// binds to are returned as-is; anything else (function, composition, `any`, attributed, … types)
+/// is parenthesized so e.g. `(Int) -> Void` becomes `((Int) -> Void)?` rather than `(Int) -> Void?`.
+private func needsParenthesesBeforeOptional(_ type: TypeSyntax) -> Bool {
+  switch type.as(TypeSyntaxEnum.self) {
+  case .identifierType, .memberType, .arrayType, .dictionaryType, .optionalType,
+    .implicitlyUnwrappedOptionalType, .tupleType, .metatypeType:
+    return false
+  default:
+    return true
+  }
+}
+
+/// The enclosing enum's indentation and the file's inferred indentation step.
+private func accessorIndentation(for enumDecl: EnumDeclSyntax) -> (base: Trivia, step: Trivia) {
+  let base = enumDecl.firstToken(viewMode: .sourceAccurate)?.indentationOfLine ?? []
+  let step = BasicFormat.inferIndentation(of: enumDecl.root) ?? .spaces(4)
+  return (base: base, step: step)
+}
+
+private func sourceEdits(insertingAccessors accessors: [String], into enumDecl: EnumDeclSyntax) throws -> [SourceEdit] {
+  guard !accessors.isEmpty else {
+    throw RefactoringNotApplicableError("No accessors to generate")
+  }
+  // Insert before the closing brace's leading trivia so the brace keeps its own
+  // newline and indentation (correct for both top-level and nested enums).
+  let insertion = "\n\n" + accessors.joined(separator: "\n\n")
+  let position = enumDecl.memberBlock.rightBrace.position
+  return [SourceEdit(range: position..<position, replacement: insertion)]
+}

Sources/SwiftSyntaxCodeActions/SyntaxCodeActions.swift

@@ -27,6 +27,8 @@ package let allSyntaxCodeActions: [any SyntaxCodeActionProvider.Type] = {
     ConvertStringConcatenationToStringInterpolation.self,
     ConvertZeroParameterFunctionToComputedProperty.self,
     FormatRawStringLiteral.self,
+    GenerateEnumCaseAsAccessors.self,
+    GenerateEnumCaseIsAccessors.self,
     MigrateToNewIfLetSyntax.self,
     OpaqueParameterToGeneric.self,
     RemoveRedundantParentheses.self,