How to Test the New Swift Build System in Swift 6.3

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Introduction

Swift 6.3 marks a major milestone for cross‑platform development. The headline feature is the integration of Swift Build into Swift Package Manager (SPM), merging two separate build technologies into one consistent system. This guide walks you through enabling and testing this new build system on your own projects—so you can experience the improved performance and unified toolchain before it becomes the default. By following these steps, you’ll also help the community iron out remaining issues.

What You Need

• A machine running macOS, Linux, or Windows that supports Swift 6.3 (see Swift.org/download for platform requirements).
• The Swift 6.3 toolchain installed (either from the official installer or via a package manager like Homebrew or apt).
• At least one Swift Package you can test—either your own or any open‑source package from the Swift Package Index.
• Basic familiarity with the terminal and running Swift Package Manager commands.
• Optional: a GitHub account to file bug reports.

Step‑by‑Step Guide

1. Install or Update to Swift 6.3
   If you don’t already have Swift 6.3, download the latest snapshot from swift.org/download and follow the platform‑specific install instructions. Verify the installation:

   swift --version

   You should see output containing “Swift 6.3”.
2. Enable the Swift Build Integration
   Swift Build is opt‑in for this release. To test it, set the environment variable SWIFTPM_USE_SWIFT_BUILD to true before running SPM commands. On macOS/Linux:

   export SWIFTPM_USE_SWIFT_BUILD=true

   On Windows (PowerShell):

   $env:SWIFTPM_USE_SWIFT_BUILD = "true"

   Alternatively, you can pass the flag --use-swift-build to individual swift build or swift test commands.
3. Build a Simple Package
   Start with a package you know works. Navigate to its root directory and run:

   swift build

   The first build may take slightly longer as Swift Build indexes the project. Watch for success messages and verify that the binaries are generated in .build/debug.
4. Run Tests
   To confirm the build system also handles test targets correctly:

   swift test --use-swift-build

   If your package has no tests, create a minimal test file or skip this step.
5. Test a Diverse Set of Packages
   For a more thorough evaluation, test a handful of packages from different domains. The Swift Build team recommends using the Swift Package Index’s top packages. Try building and testing 5–10 popular packages that cover various dependencies, build settings, and platform requirements.
   Pro tip: Use a script to automate the process, or manually clone and build each package.
6. Report Any Issues
   If you encounter a crash, incorrect behavior, or a build failure that does not occur with the default build system (i.e., without the flag), file a bug report on the Swift Build GitHub issue tracker. Include:
   • The exact SPM command you ran
   • Your platform and Swift version
   • A minimal reproduction case (preferably a public package)
   • The full error output
7. Stay Informed About Updates
   The Swift Build team posts progress updates on the Swift Forums. For video overviews, check out the talks mentioned in the community section below: “The -ization of Containerization” and “Real‑time Computer Vision on NVIDIA Jetson”—both showcase Swift in new domains.

Tips for a Smooth Experience

• Back up your projects before enabling Swift Build, especially if you’re working on a production codebase. The integration is still experimental.
• Use a separate branch or a copy of your repository when testing, to keep your main development environment clean.
• Pay attention to warnings – Swift Build may emit deprecation notices or suggestions that help you future‑proof your package.
• Leverage community resources: The step‑by‑step guide above is just the start. Listen to the Swift Academy podcast interview with Matt Massicotte on concurrency, and follow the Swift for Wasm updates to see how the ecosystem evolves.
• Watch for API deprecation strategies – If you maintain a library, the Hard Deprecations and Soft Landings article on Point‑Free shows how to use SwiftPM traits to ease migrations.
• Join the conversation in the Swift Forums and share your testing results. Your feedback directly shapes the future default build system.

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