swift-ci-portability

# Swift CI & Portability ## Overview Two jobs, one skill: get a SwiftPM project onto GitHub Actions CI quickly, and stop (or diagnose) the specific class of bug where tests pass on a developer's Mac but fail on CI - or pass on one CI runner and fail on another. ## Prerequisites - A Swift Package Manager project (`Package.swift`) hosted on GitHub with Actions enabled. - `swift` toolchain locally for reproducing CI failures. ## When to use this - Setting up CI for a SwiftPM package/app for the first time. - A test suite is green locally but red on GitHub Actions (or red on one matrix row and green on another). - You're about to write code that touches dates, locales, number formatting, file paths, or bundled resources, and want to avoid known traps up front rather than debug them later. ## Instructions Setting up GitHub Actions CI: 1. Copy the template workflow into the repo: ```bash mkdir -p .github/workflows cp assets/ci.yml.template .github/workflows/ci.yml ``` 2. Open `.github/workflows/ci.yml` and adjust to the project: - **Runner image / Xcode version** - the `test` job pins one macOS/Xcode combination as the fast required check. Pick versions that match what your team actually develops against. Check currently available images and their preinstalled Xcode versions at https://github.com/actions/runner-images (search the macOS READMEs) before picking a runner label like `macos-14` or `macos-15`. - **Matrix rows*...