How to migrate to Swift 6

To migrate to Swift 6, you can follow a structured process that ensures your codebase transitions smoothly while taking advantage of the new features and safety guarantees. Here are the key steps and considerations:

1. Enable Complete Concurrency Checking:

   • Start by enabling complete concurrency checking on a per-module basis. This will leave your project in Swift 5 mode but will enable warnings for code that would fail under Swift 6's enforced data isolation.
   • Resolve all the warnings for each target before moving to the next step.

2. Enable Swift 6 Mode:

   • Once all warnings are resolved for a target, enable Swift 6 mode for that target. This locks in your changes and prevents future regressions to unsafe states.
   • Repeat this process for each target in your project.

3. Incremental Migration:

   • You can migrate your code incrementally, one module at a time. This approach allows you to adopt Swift 6 without needing to wait for all dependencies to migrate.
   • You can interoperate with dependencies that may or may not have migrated to Swift 6 language mode.

4. Compiler Diagnostics:

   • Use the compiler diagnostics to guide you towards places in your code that need fixing. Think of it as a pair programmer pointing out potential bugs.
   • This helps add structure to the migration process and ensures you don't miss any critical changes.

5. Data Race Safety:

   • Swift 6 introduces compile-time data race safety. When you turn on the Swift 6 language mode, the compiler will diagnose concurrent access to memory across your project.
   • Fix data race safety errors with narrow changes to your code.

6. Public Swift Packages:

   • If you maintain a public Swift package, adopt Swift 6 as soon as possible to help your users who want to migrate their codebases. This benefits the community by building on top of dependencies that have also adopted Swift 6.

7. Migration Guide:

   • Follow the migration guide available on swift.org for detailed insights and patterns on how best to modify your code to eliminate data races.

For a hands-on tutorial and best practices on migration, you can refer to the session Migrate your app to Swift 6 (04:40).

Relevant Sessions

1. Platforms State of the Union (31:22)
2. What’s new in Swift (26:07)
3. Migrate your app to Swift 6 (04:40)

These sessions provide comprehensive information on the new features in Swift 6, the migration process, and practical examples to help you transition your codebase effectively.