Add refactoring action to move members to extension

Sources/SwiftLanguageService/CodeActions/MoveMembersToExtension.swift

@@ -0,0 +1,169 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+@_spi(SourceKitLSP) import LanguageServerProtocol
+import SwiftRefactor
+import SwiftSyntax
+
+private enum ValidationResult: CustomStringConvertible {
+  case accessor
+  case deinitializer
+  case enumCase
+  case storedProperty
+
+  var description: String {
+    switch self {
+    case .accessor: return "accessor"
+    case .deinitializer: return "deinitializer"
+    case .enumCase: return "enum case"
+    case .storedProperty: return "stored property"
+    }
+  }
+
+  /// Validates that `member` can be moved to an extension. If it can, return `nil`, otherwise return the reason why
+  /// `member` cannot be moved to an extension.
+  init?(_ member: MemberBlockItemSyntax) {
+    switch member.decl.kind {
+    case .accessorDecl:
+      self = .accessor
+    case .deinitializerDecl:
+      self = .deinitializer
+    case .enumCaseDecl:
+      self = .enumCase
+    default:
+      if let varDecl = member.decl.as(VariableDeclSyntax.self),
+        varDecl.bindings.contains(where: { $0.accessorBlock == nil || $0.initializer != nil })
+      {
+        self = .storedProperty
+      } else {
+        return nil
+      }
+    }
+  }
+}
+
+struct MoveMembersToExtension: SyntaxRefactoringProvider {
+  struct Context {
+    let range: Range<AbsolutePosition>
+
+    init(range: Range<AbsolutePosition>) {
+      self.range = range
+    }
+  }
+
+  static func refactor(syntax: SourceFileSyntax, in context: Context) throws -> SourceFileSyntax {
+    guard
+      let statement = syntax.statements.first(where: { $0.item.range.contains(context.range) }),
+      let decl = statement.item.asProtocol((any NamedDeclSyntax).self),
+      let declGroup = statement.item.asProtocol((any DeclGroupSyntax).self),
+      let statementIndex = syntax.statements.index(of: statement)
+    else {
+      throw RefactoringNotApplicableError("Type declaration not found")
+    }
+
+    let selectedMembers = Array(declGroup.memberBlock.members).filter { context.range.overlaps($0.trimmedRange) }
+      .map { (member: $0, validationResult: ValidationResult($0)) }
+
+    var membersToMove = selectedMembers.filter({ $0.validationResult == nil }).map(\.member)
+
+    guard !membersToMove.isEmpty else {
+      let notMovedMembers = Set(selectedMembers.compactMap(\.validationResult))
+        .map(\.description)
+        .sorted().joined(separator: ", ")
+      throw RefactoringNotApplicableError(
+        "Cannot move \(notMovedMembers) to extension"
+      )
+    }
+
+    var updatedDeclGroup = declGroup
+    var remainingMembers = Array(declGroup.memberBlock.members).filter { !membersToMove.contains($0) }
+    membersToMove[0].decl.leadingTrivia = membersToMove[0].decl.leadingTrivia.trimmingPrefix(while: \.isSpaceOrTab)
+
+    if remainingMembers.isEmpty {
+      updatedDeclGroup.memberBlock.rightBrace.leadingTrivia = Trivia()
+    } else {
+      remainingMembers[0].leadingTrivia = .newline.merging(
+        remainingMembers[0].leadingTrivia.trimmingPrefix(while: \.isNewline)
+      )
+      remainingMembers[remainingMembers.count - 1].trailingTrivia = remainingMembers[remainingMembers.count - 1]
+        .trailingTrivia.trimmingSuffix(while: \.isNewline)
+    }
+
+    updatedDeclGroup.memberBlock.members = MemberBlockItemListSyntax(remainingMembers)
+    membersToMove[0].leadingTrivia = .newline.merging(membersToMove[0].leadingTrivia.trimmingPrefix(while: \.isNewline))
+    let extensionMemberBlockSyntax = declGroup.memberBlock.with(\.members, MemberBlockItemListSyntax(membersToMove))
+
+    var declName = decl.name
+    declName.trailingTrivia = declName.trailingTrivia.merging(.space)
+
+    let extensionDecl = ExtensionDeclSyntax(
+      leadingTrivia: .newlines(2),
+      extendedType: IdentifierTypeSyntax(
+        leadingTrivia: .space,
+        name: declName
+      ),
+      memberBlock: extensionMemberBlockSyntax
+    )
+
+    var syntax = syntax
+    let updatedStatement = statement.with(\.item, .decl(DeclSyntax(updatedDeclGroup)))
+    syntax.statements[statementIndex] = updatedStatement
+    syntax.statements.insert(
+      CodeBlockItemSyntax(item: .decl(DeclSyntax(extensionDecl))),
+      at: syntax.statements.index(after: statementIndex)
+    )
+    return syntax
+  }
+}
+
+extension MoveMembersToExtension: SyntaxRefactoringCodeActionProvider {
+  static var title: String { "Move to extension" }
+
+  static func refactoringContext(for scope: SyntaxCodeActionScope) -> Context {
+    Context(range: scope.range)
+  }
+
+  static func nodeToRefactor(in scope: SyntaxCodeActionScope) -> SourceFileSyntax? {
+    guard scope.request.range.lowerBound != scope.request.range.upperBound else {
+      return nil
+    }
+
+    return scope.file
+  }
+
+  static func textRefactor(syntax: SourceFileSyntax, in context: Context) throws -> [SourceEdit] {
+    let updatedSyntax = try self.refactor(syntax: syntax, in: context)
+
+    return [
+      .replace(syntax, with: updatedSyntax.description)
+    ]
+  }
+}
+
+fileprivate extension Trivia {
+  func trimmingPrefix(
+    while predicate: (TriviaPiece) -> Bool
+  ) -> Trivia {
+    Trivia(pieces: self.drop(while: predicate))
+  }
+
+  func trimmingSuffix(
+    while predicate: (TriviaPiece) -> Bool
+  ) -> Trivia {
+    Trivia(
+      pieces: self[...]
+        .reversed()
+        .drop(while: predicate)
+        .reversed()
+    )
+  }
+}

Sources/SwiftLanguageService/CodeActions/SyntaxCodeActions.swift

@@ -28,6 +28,7 @@ let allSyntaxCodeActions: [any SyntaxCodeActionProvider.Type] = {
     ConvertZeroParameterFunctionToComputedProperty.self,
     FormatRawStringLiteral.self,
     MigrateToNewIfLetSyntax.self,
+    MoveMembersToExtension.self,
     OpaqueParameterToGeneric.self,
     RemoveRedundantParentheses.self,
     RemoveSeparatorsFromIntegerLiteral.self,
@@ -41,5 +42,6 @@ let allSyntaxCodeActions: [any SyntaxCodeActionProvider.Type] = {
 
 let supersededSourcekitdRefactoringActions: Set<String> = [
   "source.refactoring.kind.convert.to.computed.property",  // Superseded by ConvertStoredPropertyToComputed
+  "source.refactoring.kind.move.members.to.extension",  // Superseded by MoveMembersToExtension
   "source.refactoring.kind.simplify.long.number.literal",  // Superseded by AddSeparatorsToIntegerLiteral
 ]