Refactor MoveMembersToExtension

Sources/SwiftRefactor/MoveMembersToExtension.swift

@@ -0,0 +1,86 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#if compiler(>=6)
+public import SwiftSyntax
+#else
+import SwiftSyntax
+#endif
+
+public struct MoveMembersToExtension: SyntaxRefactoringProvider {
+
+  public struct Context {
+    public let declName: TokenSyntax
+    public let selectedIdentifiers: [SyntaxIdentifier]
+
+    public init(declName: TokenSyntax, selectedIdentifiers: [SyntaxIdentifier]) {
+      self.declName = declName
+      self.selectedIdentifiers = selectedIdentifiers
+    }
+  }
+
+  public static func refactor(syntax: SourceFileSyntax, in context: Context) throws -> SourceFileSyntax {
+    guard
+      let decl = syntax.statements.first(where: {
+        $0.item.asProtocol(NamedDeclSyntax.self)?.name == context.declName
+      }),
+      let declGroup = decl.item.asProtocol(DeclGroupSyntax.self),
+      let index = syntax.statements.index(of: decl)
+    else {
+      throw RefactoringNotApplicableError("Type declaration not found")
+    }
+
+    let selectedMembers = declGroup.memberBlock.members.filter { context.selectedIdentifiers.contains($0.id) }
+
+    for member in selectedMembers {
+      try validateMember(member)
+    }
+
+    let remainingMembers = declGroup.memberBlock.members.filter { !context.selectedIdentifiers.contains($0.id) }
+
+    let updatedMemberBlock = declGroup.memberBlock.with(\.members, remainingMembers)
+    let updatedDeclGroup = declGroup.with(\.memberBlock, updatedMemberBlock)
+    let updatedItem = decl.with(\.item, .decl(DeclSyntax(updatedDeclGroup)))
+
+    let extensionMemberBlockSyntax = declGroup.memberBlock.with(\.members, selectedMembers)
+
+    let extensionDecl = ExtensionDeclSyntax(
+      leadingTrivia: .newlines(2),
+      extendedType: IdentifierTypeSyntax(
+        leadingTrivia: .space,
+        name: context.declName
+      ),
+      memberBlock: extensionMemberBlockSyntax
+    )
+
+    var updatedStatements = syntax.statements
+    updatedStatements.remove(at: index)
+    updatedStatements.insert(updatedItem, at: index)
+    updatedStatements.append(CodeBlockItemSyntax(item: .decl(DeclSyntax(extensionDecl))))
+
+    return syntax.with(\.statements, updatedStatements)
+  }
+
+  private static func validateMember(_ member: MemberBlockItemSyntax) throws {
+    if member.decl.is(AccessorDeclSyntax.self) || member.decl.is(DeinitializerDeclSyntax.self)
+      || member.decl.is(EnumCaseDeclSyntax.self)
+    {
+      throw RefactoringNotApplicableError("Cannot move this type of declaration")
+    }
+
+    if let varDecl = member.decl.as(VariableDeclSyntax.self),
+      varDecl.bindings.contains(where: { $0.initializer == nil })
+    {
+      throw RefactoringNotApplicableError("Cannot move stored properties to extension")
+    }
+  }
+}

Tests/SwiftRefactorTest/MoveMembersToExtensionTests.swift

@@ -0,0 +1,90 @@
+//===----------------------------------------------------------------------===//
+//
+// 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 SwiftParser
+import SwiftRefactor
+import SwiftSyntax
+import SwiftSyntaxBuilder
+import XCTest
+import _SwiftSyntaxTestSupport
+
+final class MoveMembersToExtensionTests: XCTestCase {
+  func testMoveFunctionToExtension() throws {
+    let baseline: String = """
+      class Foo {1️⃣
+        func foo() {
+          print("Hello world!")
+        }2️⃣
+
+        func bar() {
+          print("Hello world!")
+        }
+      }
+      """
+
+    let expected: SourceFileSyntax = """
+      class Foo {
+
+        func bar() {
+          print("Hello world!")
+        }
+      }
+
+      extension Foo {
+        func foo() {
+          print("Hello world!")
+        }
+      }
+      """
+
+    let (markers, source) = extractMarkers(baseline)
+
+    var parser = Parser(source)
+    let tree = SourceFileSyntax.parse(from: &parser)
+    let context = makeContextFromClass(markers: markers, source: tree)
+    try assertRefactorConvert(tree, expected: expected, context: context)
+  }
+}
+
+private func makeContextFromClass(markers: [String: Int], source: SourceFileSyntax) -> MoveMembersToExtension.Context {
+  let classDecl = source.statements
+    .first(where: { $0.item.is(ClassDeclSyntax.self) })!
+    .item.cast(ClassDeclSyntax.self)
+  let members = classDecl.memberBlock.members
+
+  let selectedMembersId: [SyntaxIdentifier] = members.compactMap({
+    let offset = $0.positionAfterSkippingLeadingTrivia.utf8Offset
+    if let start = markers["1️⃣"], let end = markers["2️⃣"], offset > start && offset < end {
+      return $0.id
+    }
+    return nil
+  })
+
+  return MoveMembersToExtension.Context(declName: classDecl.name, selectedIdentifiers: selectedMembersId)
+}
+
+private func assertRefactorConvert(
+  _ callDecl: SourceFileSyntax,
+  expected: SourceFileSyntax?,
+  context: MoveMembersToExtension.Context,
+  file: StaticString = #filePath,
+  line: UInt = #line
+) throws {
+  try assertRefactor(
+    callDecl,
+    context: context,
+    provider: MoveMembersToExtension.self,
+    expected: expected,
+    file: file,
+    line: line
+  )
+}