[Commands] Prototype swift-fixit — a subcommand for deserializing diagnostics and applying fix-its

Fixtures/SwiftFixIt/SwiftFixItPackage/Package.swift

@@ -0,0 +1,10 @@
+// swift-tools-version:5.9
+
+import PackageDescription
+
+let package = Package(
+    name: "SwiftFixItPackage",
+    targets: [
+        .target(name: "Diagnostics", path: "Sources", exclude: ["Fixed"]),
+    ]
+)

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/Fixed/first.swift

@@ -0,0 +1,12 @@
+func foo(_: any P, _: any P) {}
+
+func throwing() throws -> Int {}
+
+func foo() throws {
+    do {
+        _ = 0
+    }
+    do {
+        _ = try throwing()
+    }
+}

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/Fixed/second.swift

@@ -0,0 +1,5 @@
+protocol P {
+    associatedtype A
+}
+
+func bar(_: any P) {}

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/first.swift

@@ -0,0 +1,12 @@
+func foo(_: P, _: P) {}
+
+func throwing() throws -> Int {}
+
+func foo() throws {
+    do {
+        var x = 0
+    }
+    do {
+        let x = throwing()
+    }
+}

Fixtures/SwiftFixIt/SwiftFixItPackage/Sources/second.swift

@@ -0,0 +1,5 @@
+protocol P {
+    associatedtype A
+}
+
+func bar(_: P) {}

Package.swift

@@ -588,6 +588,7 @@ let package = Package(
                 "Workspace",
                 "XCBuildSupport",
                 "SwiftBuildSupport",
+                "SwiftFixIt",
             ] + swiftSyntaxDependencies(["SwiftIDEUtils"]),
             exclude: ["CMakeLists.txt", "README.md"],
             swiftSettings: swift6CompatibleExperimentalFeatures + [
@@ -745,6 +746,12 @@ let package = Package(
                 "Workspace",
             ]
         ),
+        .executableTarget(
+            /** Deserializes diagnostics and applies fix-its */
+            name: "swift-fixit",
+            dependencies: ["Commands"],
+            exclude: ["CMakeLists.txt"]
+        ),
 
         // MARK: Support for Swift macros, should eventually move to a plugin-based solution
 

Sources/Commands/CMakeLists.txt

@@ -40,6 +40,7 @@ add_library(Commands
   Snippets/Card.swift
   Snippets/Colorful.swift
   SwiftBuildCommand.swift
+  SwiftFixItCommand.swift
   SwiftRunCommand.swift
   SwiftTestCommand.swift
   CommandWorkspaceDelegate.swift

Sources/Commands/SwiftFixitCommand.swift

@@ -0,0 +1,66 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import struct ArgumentParser.Argument
+import protocol ArgumentParser.AsyncParsableCommand
+import struct ArgumentParser.CommandConfiguration
+import struct ArgumentParser.OptionGroup
+import protocol ArgumentParser.ParsableArguments
+
+import struct Basics.AbsolutePath
+import var Basics.localFileSystem
+import struct Basics.SwiftVersion
+
+import struct CoreCommands.LoggingOptions
+
+import struct SwiftFixIt.SwiftFixIt
+
+private struct Options: ParsableArguments {
+    @OptionGroup(title: "Logging")
+    var logging: LoggingOptions
+
+    @Argument(
+        help: "",
+        completion: .file(extensions: [".dia"])
+    )
+    var diagnosticFiles: [AbsolutePath] = []
+}
+
+/// Deserializes `.dia` files and applies all fix-its in place.
+package struct SwiftFixitCommand: AsyncParsableCommand {
+    package static var configuration = CommandConfiguration(
+        commandName: "fixit",
+        _superCommandName: "swift",
+        abstract: "Deserialize diagnostics and apply fix-its",
+        version: SwiftVersion.current.completeDisplayString,
+        helpNames: [
+            .short,
+            .long,
+            .customLong("help", withSingleDash: true),
+        ]
+    )
+
+    @OptionGroup
+    fileprivate var options: Options
+
+    package init() {}
+
+    package func run() async throws {
+        if self.options.diagnosticFiles.isEmpty {
+            return
+        }
+
+        let swiftFixIt = try SwiftFixIt(diagnosticFiles: options.diagnosticFiles, fileSystem: localFileSystem)
+
+        try swiftFixIt.applyFixIts()
+    }
+}

Sources/_InternalTestSupport/SwiftPMProduct.swift

@@ -29,6 +29,7 @@ public enum SwiftPM {
     case Run
     case experimentalSDK
     case sdk
+    case fixit
 }
 
 extension SwiftPM {
@@ -49,6 +50,8 @@ extension SwiftPM {
             return "swift-experimental-sdk"
         case .sdk:
             return "swift-sdk"
+        case .fixit:
+            return "swift-fixit"
         }
     }
 

Sources/swift-fixit/CMakeLists.txt

@@ -0,0 +1,18 @@
+# This source file is part of the Swift open source project
+#
+# Copyright (c) 2025 Apple Inc. and the Swift project authors
+# Licensed under Apache License v2.0 with Runtime Library Exception
+#
+# See http://swift.org/LICENSE.txt for license information
+# See http://swift.org/CONTRIBUTORS.txt for Swift project authors
+
+add_executable(swift-fixit
+  Entrypoint.swift)
+target_link_libraries(swift-test PRIVATE
+  Commands)
+
+target_compile_options(swift-test PRIVATE
+  -parse-as-library)
+
+install(TARGETS swift-fixit
+  RUNTIME DESTINATION bin)

Sources/swift-fixit/Entrypoint.swift

@@ -0,0 +1,20 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Commands
+
+@main
+struct Entrypoint {
+    static func main() async {
+        await SwiftFixitCommand.main()
+    }
+}

Sources/swift-package-manager/SwiftPM.swift

@@ -54,6 +54,8 @@ struct SwiftPM {
             await PackageCollectionsCommand.main()
         case "swift-package-registry":
             await PackageRegistryCommand.main()
+        case "swift-fixit":
+            await SwiftFixitCommand.main()
         default:
             fatalError("swift-package-manager launched with unexpected name: \(execName ?? "(unknown)")")
         }

Tests/CommandsTests/SwiftFixItCommandTests.swift

@@ -0,0 +1,82 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See http://swift.org/LICENSE.txt for license information
+// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import _InternalTestSupport
+import struct Basics.AbsolutePath
+import var Basics.localFileSystem
+@testable
+import Commands
+import class PackageModel.UserToolchain
+import XCTest
+
+final class FixItCommandTests: CommandsTestCase {
+    func testHelp() async throws {
+        let stdout = try await SwiftPM.fixit.execute(["-help"]).stdout
+
+        XCTAssert(stdout.contains("USAGE: swift fixit"), stdout)
+        XCTAssert(stdout.contains("-h, -help, --help"), stdout)
+    }
+
+    func testApplyFixIts() async throws {
+        try await fixture(name: "SwiftFixIt/SwiftFixItPackage") { fixturePath in
+            let sourcePaths: [AbsolutePath]
+            let fixedSourcePaths: [AbsolutePath]
+            do {
+                let sourcesPath = fixturePath.appending(components: "Sources")
+                let fixedSourcesPath = sourcesPath.appending("Fixed")
+
+                sourcePaths = try localFileSystem.getDirectoryContents(sourcesPath).filter { filename in
+                    filename.hasSuffix(".swift")
+                }.sorted().map { filename in
+                    sourcesPath.appending(filename)
+                }
+                fixedSourcePaths = try localFileSystem.getDirectoryContents(fixedSourcesPath).filter { filename in
+                    filename.hasSuffix(".swift")
+                }.sorted().map { filename in
+                    fixedSourcesPath.appending(filename)
+                }
+            }
+
+            XCTAssertEqual(sourcePaths.count, fixedSourcePaths.count)
+
+            let targetName = "Diagnostics"
+
+            _ = try? await executeSwiftBuild(fixturePath, extraArgs: ["--target", targetName])
+
+            do {
+                let artifactsPath = try fixturePath.appending(
+                    components: ".build",
+                    UserToolchain.default.targetTriple.platformBuildPathComponent,
+                    "debug",
+                    "\(targetName).build"
+                )
+                let diaFilePaths = try localFileSystem.getDirectoryContents(artifactsPath).filter { filename in
+                    // Ignore "*.emit-module.dia".
+                    filename.split(".").1 == "dia"
+                }.map { filename in
+                    artifactsPath.appending(component: filename).pathString
+                }
+
+                XCTAssertEqual(sourcePaths.count, diaFilePaths.count)
+
+                _ = try await SwiftPM.fixit.execute(diaFilePaths)
+            }
+
+            for (sourcePath, fixedSourcePath) in zip(sourcePaths, fixedSourcePaths) {
+                try XCTAssertEqual(
+                    localFileSystem.readFileContents(sourcePath),
+                    localFileSystem.readFileContents(fixedSourcePath)
+                )
+            }
+        }
+    }
+}