Bump tools version to 6.0 and make the package build in Swift 6 mode

Author: AnthonyLatsis

Package.swift

@@ -1,9 +1,9 @@
-// swift-tools-version: 5.9
+// swift-tools-version: 6.0
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2025 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
@@ -47,7 +47,11 @@ var targets: [Target] = [
       + swiftSyntaxDependencies([
         "SwiftOperators", "SwiftParser", "SwiftParserDiagnostics", "SwiftSyntax", "SwiftSyntaxBuilder",
       ]),
-    exclude: ["CMakeLists.txt"]
+    exclude: ["CMakeLists.txt"],
+    swiftSettings: [
+      // TODO: Does not compile with Swift 6 in Swift 6 mode due to Swift concurrency bugs. Remove once swift-tools-version is bumped to 6.1.
+      .swiftLanguageMode(.v5)
+    ]
   ),
   .target(
     name: "_SwiftFormatTestSupport",
@@ -146,9 +150,11 @@ let package = Package(
   ],
   products: products,
   dependencies: dependencies,
-  targets: targets
+  targets: targets,
+  swiftLanguageModes: [.v5, .v6]
 )
 
+@MainActor
 func swiftSyntaxDependencies(_ names: [String]) -> [Target.Dependency] {
   if buildDynamicSwiftSyntaxLibrary {
     return [.product(name: "_SwiftSyntaxDynamic", package: "swift-syntax")]

Sources/SwiftFormat/API/Configuration.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2023 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2025 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
@@ -22,7 +22,7 @@ import Foundation
 internal let highestSupportedConfigurationVersion = 1
 
 /// Holds the complete set of configured values and defaults.
-public struct Configuration: Codable, Equatable {
+public struct Configuration: Codable, Equatable, Sendable {
 
   private enum CodingKeys: CodingKey {
     case version
@@ -176,7 +176,7 @@ public struct Configuration: Codable, Equatable {
   public var noAssignmentInExpressions: NoAssignmentInExpressionsConfiguration
 
   /// Determines how trailing commas in comma-separated lists should be handled during formatting.
-  public enum MultilineTrailingCommaBehavior: String, Codable {
+  public enum MultilineTrailingCommaBehavior: String, Codable, Sendable {
     case alwaysUsed
     case neverUsed
     case keptAsWritten
@@ -215,7 +215,7 @@ public struct Configuration: Codable, Equatable {
   public var multiElementCollectionTrailingCommas: Bool
 
   /// Determines how multiline string literals should reflow when formatted.
-  public enum MultilineStringReflowBehavior: String, Codable {
+  public enum MultilineStringReflowBehavior: String, Codable, Sendable {
     /// Never reflow multiline string literals.
     case never
     /// Reflow lines in string literal that exceed the maximum line length. For example with a line length of 10:
@@ -524,8 +524,8 @@ public struct Configuration: Codable, Equatable {
 }
 
 /// Configuration for the `FileScopedDeclarationPrivacy` rule.
-public struct FileScopedDeclarationPrivacyConfiguration: Codable, Equatable {
-  public enum AccessLevel: String, Codable {
+public struct FileScopedDeclarationPrivacyConfiguration: Codable, Equatable, Sendable {
+  public enum AccessLevel: String, Codable, Sendable {
     /// Private file-scoped declarations should be declared `private`.
     ///
     /// If a file-scoped declaration is declared `fileprivate`, it will be diagnosed (in lint mode)
@@ -547,7 +547,7 @@ public struct FileScopedDeclarationPrivacyConfiguration: Codable, Equatable {
 }
 
 /// Configuration for the `NoAssignmentInExpressions` rule.
-public struct NoAssignmentInExpressionsConfiguration: Codable, Equatable {
+public struct NoAssignmentInExpressionsConfiguration: Codable, Equatable, Sendable {
   /// A list of function names where assignments are allowed to be embedded in expressions that are
   /// passed as parameters to that function.
   public var allowedFunctions: [String] = [
@@ -561,7 +561,7 @@ public struct NoAssignmentInExpressionsConfiguration: Codable, Equatable {
 }
 
 /// Configuration for the `OrderedImports` rule.
-public struct OrderedImportsConfiguration: Codable, Equatable {
+public struct OrderedImportsConfiguration: Codable, Equatable, Sendable {
   /// Determines whether imports within conditional compilation blocks should be ordered.
   public var includeConditionalImports: Bool = false
 

Sources/SwiftFormat/API/DebugOptions.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2025 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
@@ -12,7 +12,7 @@
 
 /// Advanced options that are useful when debugging and developing the formatter, but are otherwise
 /// not meant for general use.
-public struct DebugOptions: OptionSet {
+public struct DebugOptions: OptionSet, Sendable {
 
   /// Disables the pretty-printer pass entirely, executing only the syntax-transforming rules in the
   /// pipeline.

Sources/SwiftFormat/API/Finding.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2025 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
@@ -39,7 +39,7 @@ public struct Finding {
   /// an `extension` of the `Finding.Message` type and add `static` properties or functions of type
   /// `Finding.Message`; these can be initialized using string literals or string interpolations.
   public struct Message:
-    CustomStringConvertible, ExpressibleByStringLiteral, ExpressibleByStringInterpolation
+    CustomStringConvertible, ExpressibleByStringLiteral, ExpressibleByStringInterpolation, Sendable
   {
     /// The message text of the diagnostic.
     public var text: String

Sources/SwiftFormat/API/Indent.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2025 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
@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 /// Represents an indentation unit that is applied to lines that are pretty-printed.
-public enum Indent: Hashable, Codable {
+public enum Indent: Hashable, Codable, Sendable {
 
   /// An indentation unit equal to the given number of tab characters.
   ///

Sources/SwiftFormat/API/Selection.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2024 Apple Inc. and the Swift project authors
+// Copyright (c) 2024 - 2025 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
@@ -14,7 +14,7 @@ import Foundation
 import SwiftSyntax
 
 /// The selection as given on the command line - an array of offets and lengths
-public enum Selection {
+public enum Selection: Sendable {
   case infinite
   case ranges([Range<AbsolutePosition>])
 

Sources/SwiftFormat/Core/RuleMask.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2025 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
@@ -124,6 +124,9 @@ enum IgnoreDirective: CustomStringConvertible {
   }
 }
 
+// This regex is thread-safe.
+extension IgnoreDirective.RegexExpression: @unchecked @retroactive Sendable {}
+
 /// A syntax visitor that finds `SourceRange`s of nodes that have rule status modifying comment
 /// directives. The changes requested in each comment is parsed and collected into a map to support
 /// status lookup per rule name.

Sources/SwiftFormat/Rules/BeginDocumentationCommentWithOneLineSummary.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2019 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2025 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
@@ -29,7 +29,7 @@ public final class BeginDocumentationCommentWithOneLineSummary: SyntaxLintRule {
   /// even on platforms that support the latter (currently only Apple OSes).
   ///
   /// This allows test runs on those platforms to test both implementations.
-  public static var _forcesFallbackModeForTesting = false
+  nonisolated(unsafe) package static var _forcesFallbackModeForTesting = false
 
   /// Identifies this rule as being opt-in. Well written docs on declarations are important, but
   /// this rule isn't linguistically advanced enough on all platforms to be applied universally.

Sources/_SwiftFormatTestSupport/DiagnosingTestCase.swift

@@ -48,7 +48,7 @@ open class DiagnosingTestCase: XCTestCase {
     markerLocations: [String: Int],
     emittedFindings: [Finding],
     context: Context,
-    file: StaticString = #file,
+    file: StaticString = #filePath,
     line: UInt = #line
   ) {
     var emittedFindings = emittedFindings
@@ -86,7 +86,7 @@ open class DiagnosingTestCase: XCTestCase {
     markerLocations: [String: Int],
     emittedFindings: inout [Finding],
     context: Context,
-    file: StaticString = #file,
+    file: StaticString = #filePath,
     line: UInt = #line
   ) {
     guard let utf8Offset = markerLocations[findingSpec.marker] else {
@@ -164,7 +164,7 @@ open class DiagnosingTestCase: XCTestCase {
     markerLocations: [String: Int],
     emittedNotes: inout [Finding.Note],
     context: Context,
-    file: StaticString = #file,
+    file: StaticString = #filePath,
     line: UInt = #line
   ) {
     guard let utf8Offset = markerLocations[noteSpec.marker] else {
@@ -222,7 +222,7 @@ open class DiagnosingTestCase: XCTestCase {
     _ actual: String,
     _ expected: String,
     _ message: String = "",
-    file: StaticString = #file,
+    file: StaticString = #filePath,
     line: UInt = #line
   ) {
     let actualLines = actual.components(separatedBy: .newlines)

Sources/swift-format/Frontend/ConfigurationLoader.swift

@@ -15,7 +15,7 @@ import SwiftFormat
 
 /// Loads formatter configurations, caching them in memory so that multiple operations in the same
 /// directory do not repeatedly hit the file system.
-struct ConfigurationLoader {
+struct ConfigurationLoader: ~Copyable {
   /// The cache of previously loaded configurations.
   private var cache = [String: Configuration]()