Build caching: Swift packages, pub cache, Bitrise caches, opt-in ccache

[Interlap01]

What

• Swift packages: every runner clones packages into ~/.ios-builder/SourcePackages (-clonedSourcePackagesDirPath on every xcodebuild that passes -derivedDataPath, and on the apply_build_number calls). GitHub caches it keyed on the workspace/project Package.resolved (excluding DerivedData, node_modules, Pods); Codemagic caches the path. Stale DerivedData/SourcePackages from older runs is deleted before the DerivedData save.
• Flutter pub cache on GitHub: own step keyed on pubspec.lock with a prefix fallback; flutter-action runs with pub-cache: false (its own pub cache had no fallback key).
• ios-share: now restores Pods, node_modules, Swift packages, pub cache and ccache, and saves each before the share step (success only, key missed, under cache-primary-key).
• Bitrise: restore-cache@3/save-cache@1 for DerivedData, Swift packages, Pods, node_modules, pub cache, Gradle and ccache. Keys checksum the snapshot's lockfiles, so the snapshot is checked out in its own step (runner.sh checkout) before the restores. The node_modules BITRISE_CACHE_HIT is aliased so an exact hit skips the install, as on GitHub. Only the per-build DerivedData/ccache saves run after a failed build.
• ccache, opt-in: "cache": {"ccache": true} in builder.json, React Native and Expo only. A shared shell block (identical in both GitHub templates and runner.sh) installs ccache and sets USE_CCACHE=1/CCACHE_DIR before pod install. ~/.ccache is cached on all three providers.
• The device DerivedData prefix is now deriveddata-device-: deriveddata- also matched the simulator workflow's deriveddata-sim-* caches.

Why ccache is opt-in

A fresh checkout gives every file a new mtime, so a restored DerivedData still recompiles React Native and its native modules. ccache matches on content, so it helps there. But the Podfile decides whether clang goes through it: React Native's react_native_post_install reads USE_CCACHE, and Expo's generated Podfile reads apple.ccacheEnabled from Podfile.properties.json. A project whose Podfile does neither gains nothing, and installing ccache costs time on every run. Native, Flutter and KMP ignore the switch.

Tests

• New internal/workflow/cache_test.go:
  • every GitHub cache/restore has a save for the same paths and a key it can find again, and in ios-share that save comes before the share step
  • cache keys and paths per workflow
  • every -derivedDataPath also passes -clonedSourcePackagesDirPath
  • the ccache block is identical across templates and runs before pod install
  • the ccache opt-in runs against a stubbed brew
  • Bitrise YAML structure: restores between checkout and build, each paired with a save, key templates evaluated, saves before the share step
  • Codemagic cache paths
• Config round-trip test for cache.ccache.
• go test -race ./..., go vet ./... and gofmt -l . are clean. golangci-lint could not run locally (the installed binary was built with Go 1.25 and the module needs 1.26). actionlint is clean on both GitHub templates. Nothing was run against a real CI provider.

Left out

• Codemagic Pods and node_modules: Codemagic caches by path with no key, so a stale copy would be restored on every build.
• -clonedSourcePackagesDirPath on xcodebuild -list, which detects the scheme. I did not confirm that -list accepts the flag, so that call still resolves packages into the default DerivedData.
• flutter build ios resolves its own Swift packages. Only the signed Flutter archive uses the cached directory.
• Existing Bitrise users need to rerun builder init --provider bitrise to get the new bitrise.yml.