[6.3] Preview the Swift Build System Integration

Overview

Swift Package Manager is previewing a new build system Swift Build as a replacement for the current native build system. This document outlines the current state of the preview, key differences, and known issues.

We encourage you to try the new build system in your project and report any issues you encounter.

For more information about the migration to Swift Build, see this forum post.

Migration plan

The Swift Build integration follows these phases:

1. Preview Phase (Current) - Testing and feedback collection

2. Feature Parity - Address remaining gaps and platform issues

3. Default Migration - Transition to Swift Build as default

4. Legacy Build System Deprecation - Phase out native and xcode build systems

How to use the Swift Build build system

To participate in the preview, run your Swift Package Manager commands with the --build-system swiftbuild flag:

swift build --build-system swiftbuild
swift test --build-system swiftbuild
swift run --build-system swiftbuild

Key improvements and differences

• --static-swift-stdlib: Stricter validation (errors instead of silently ignoring)

  • The native build system silently ignored this option on some platforms; Swift Build now produces an error.

  • The Swift Build build system will generate an error on Windows until static libraries are supported. See Upcoming changes to Windows Swift SDKs.

Detailed differences

Resource support parity with xcodebuild

• When targeting Apple platforms using --build-system swiftbuild, SwiftPM now consistently applies the same set of resource rules as xcodebuild when a package contains resource types like asset catalogs, storyboards, Metal sources, etc.

Swift Driver integration

• The --use-integrated-swift-driver command-line option is considered deprecated. --build-system swiftbuild always uses the library-based Swift driver.

• On supported platforms, --build-system swiftbuild will make use of explicitly-built Clang and Swift modules.

Enhanced diagnostics

• Logging and diagnostic differences between native and Swift Build build systems

Other

• When targeting Apple platforms, --build-system swiftbuild supports building universal binaries. Example invocation: swift build --build-system swiftbuild --arch arm64 --arch x86_64

• The Swift Build build system outputs build artifacts to a different location. Use the swift build --show-bin-path <other build arguments> to determine the build output location.

Known issues

Windows platform

• Swift Build does not support CodeView debug information format.

  • Tracking: swiftlang/swift-package-manager#9302

  • Impact: Limited debugging capabilities on Windows.

Linux platform

• Coverage reporting issues on some Linux platforms

  • Tracking: swiftlang/swift-package-manager#9600

Feature gaps

• The swift run --repl command may fail to import some modules.

  • Tracking: swiftlang/swift-package-manager#8846

• Swift Build does not provide sanitizer support for scudo and fuzzer.

  • Tracking: swiftlang/swift-package-manager#9448

  • Impact: Limited testing and debugging capabilities.

• Swift Build does not support the --enable-parseable-module-interfaces option.

  • Tracking: swiftlang/swift-package-manager#9324

• Test execution with coverage may fail on certain platforms.

  • Tracking: swiftlang/swift-package-manager#9588

• Swift SDK’s and toolset.json files aren’t working for the most part.

  • Tracking: swiftlang/swift-package-manager#9346

• Swift Build does not support test targets depending on other test targets.

  • Workaround: Create a non-test target for the test target to depend on.

  • Tracking: swiftlang/swift-package-manager#9458

• Expected native build failure in release configuration may not fail with Swift Build

  • Tracking: swiftlang/swift-package-manager#8984

• Swift Build does not support the --explicit-target-dependency-import-check flag.

  • Tracking: swiftlang/swift-package-manager#9620

• Swift Build does not pass environment variables to plugin tools.

  • Tracking: swiftlang/swift-package-manager#9122

• Swift Build does not support overlapping executable product names and library product names (case-insensitive).

  • Tracking: swiftlang/swift-package-manager#9184

Reporting issues

Please follow these steps when reporting issues:

1. Review the known issues listed above to ensure your issue has not already been identified.

2. If your issue is not listed, submit a new issue on GitHub.

3. Include the following information in your report:

   • The exact command that failed

   • Complete error output

   • System information (operating system, Swift version, etc.)

   • Whether the same command works with the native build system