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Swift

Swift CI on GitHub Actions

Swift type-checking dominates build time and nothing is reused between runs.

14m → 4m
Build
14m → 70s
Incremental

Swift type-checking dominates build time and nothing is reused between runs.

Why it happens

SwiftPM's .build directory and Xcode's DerivedData are discarded, so every run type-checks the whole module graph.

What to change

  1. Persist .build for SwiftPM and DerivedData for Xcode projects
  2. Find slow expressions with -Xfrontend -warn-long-expression-type-checking=200
  3. Split modules so a change in one does not invalidate everything
  4. Use an M4 macOS runner — Swift compilation is strongly single-thread sensitive

Swift on runnerhut

yaml
jobs:
  test:
    runs-on: runnerhut-macos-15-m4
    steps:
      - uses: actions/checkout@v4
      - run: swift build --configuration release
      - run: swift test --parallel
A working starting point

The only runnerhut-specific line is `runs-on: runnerhut-macos-15-m4`. Everything else is standard GitHub Actions — the same actions, the same secrets and the same permissions model you use today.

Your next build could be twice as fast, at half the price

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Related

RustCargo rebuilds the entire dependency graph on almost every CI run.GoGo builds are fast locally and inexplicably slow in CI.Pythonpip install takes minutes and pytest runs on a single core.Node.jsnpm ci writes tens of thousands of small files on every run.