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

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",
@@ -121,6 +125,34 @@ var targets: [Target] = [
   ),
 ]
 
+// Apply global Swift settings to targets.
+do {
+  var globalSwiftSettings: [SwiftSetting] = [
+    // Swift 7 mode upcoming features. These must be compatible with 'swift-tools-version'.
+    .enableUpcomingFeature("ExistentialAny"),
+    .enableUpcomingFeature("InternalImportsByDefault"),
+    .enableUpcomingFeature("MemberImportVisibility"),
+    .enableUpcomingFeature("NonisolatedNonsendingByDefault"),
+  ]
+
+  #if compiler(>=6.1)
+  globalSwiftSettings.append(
+    .unsafeFlags(["-Werror", "ExistentialAny"])
+  )
+  #endif
+
+  globalSwiftSettings += []  // avoid unused warning
+
+  for target in targets where target.type != .plugin {
+    if let swiftSettings = target.swiftSettings {
+      // Target-specific settings should come last.
+      target.swiftSettings = globalSwiftSettings + swiftSettings
+    } else {
+      target.swiftSettings = globalSwiftSettings
+    }
+  }
+}
+
 if buildOnlyTests {
   products = []
   let allowedNames: Set<String> = ["_SwiftFormatTestSupport", "_GenerateSwiftFormat"]
@@ -146,9 +178,11 @@ 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

@@ -2,15 +2,15 @@
 //
 // 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
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
+public import Foundation
 
 /// A version number that can be specified in the configuration file, which allows us to change the
 /// format in the future if desired and still support older files.
@@ -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:
@@ -320,7 +320,7 @@ public struct Configuration: Codable, Equatable {
     self = try jsonDecoder.decode(Configuration.self, from: data)
   }
 
-  public init(from decoder: Decoder) throws {
+  public init(from decoder: any Decoder) throws {
     let container = try decoder.container(keyedBy: CodingKeys.self)
 
     // If the version number is not present, assume it is 1.
@@ -463,7 +463,7 @@ public struct Configuration: Codable, Equatable {
       ?? defaults.rules
   }
 
-  public func encode(to encoder: Encoder) throws {
+  public func encode(to encoder: any Encoder) throws {
     var container = encoder.container(keyedBy: CodingKeys.self)
 
     try container.encode(version, forKey: .version)
@@ -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
@@ -71,7 +71,7 @@ public struct Finding {
   }
 
   /// The category associated with the finding.
-  public let category: FindingCategorizing
+  public let category: any FindingCategorizing
 
   /// The finding's message.
   public let message: Message
@@ -85,7 +85,7 @@ public struct Finding {
   /// Creates a new finding with the given category, message, optional location, and
   /// notes.
   init(
-    category: FindingCategorizing,
+    category: any FindingCategorizing,
     message: Message,
     location: Location? = nil,
     notes: [Note] = []

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.
   ///
@@ -27,7 +27,7 @@ public enum Indent: Hashable, Codable {
     case spaces
   }
 
-  public init(from decoder: Decoder) throws {
+  public init(from decoder: any Decoder) throws {
     let container = try decoder.container(keyedBy: CodingKeys.self)
     let spacesCount = try container.decodeIfPresent(Int.self, forKey: .spaces)
     let tabsCount = try container.decodeIfPresent(Int.self, forKey: .tabs)
@@ -57,7 +57,7 @@ public enum Indent: Hashable, Codable {
     )
   }
 
-  public func encode(to encoder: Encoder) throws {
+  public func encode(to encoder: any Encoder) throws {
     var container = encoder.container(keyedBy: CodingKeys.self)
     switch self {
     case .tabs(let count):

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
@@ -11,10 +11,10 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
-import SwiftSyntax
+public 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/API/SwiftFormatError.swift

@@ -2,15 +2,15 @@
 //
 // 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
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
+public import Foundation
 import SwiftSyntax
 
 /// Errors that can be thrown by the `SwiftFormatter` and `SwiftLinter` APIs.

Sources/SwiftFormat/API/SwiftFormatter.swift

@@ -2,18 +2,18 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2024 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
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
-import SwiftDiagnostics
-import SwiftOperators
-import SwiftSyntax
+public import Foundation
+public import SwiftDiagnostics
+public import SwiftOperators
+public import SwiftSyntax
 
 /// Formats Swift source code or syntax trees according to the Swift style guidelines.
 public final class SwiftFormatter {

Sources/SwiftFormat/API/SwiftLinter.swift

@@ -2,18 +2,18 @@
 //
 // 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
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
-import SwiftDiagnostics
-import SwiftOperators
-import SwiftSyntax
+public import Foundation
+public import SwiftDiagnostics
+public import SwiftOperators
+public import SwiftSyntax
 
 /// Diagnoses and reports problems in Swift source code or syntax trees according to the Swift style
 /// guidelines.

Sources/SwiftFormat/Core/Context.swift

@@ -2,18 +2,18 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2024 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
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 //
 //===----------------------------------------------------------------------===//
 
-import Foundation
-import SwiftOperators
+public import Foundation
+public import SwiftOperators
 import SwiftParser
-import SwiftSyntax
+public import SwiftSyntax
 
 /// Context contains the bits that each formatter and linter will need access to.
 ///