Cache Xcode build products in CI - #16
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Every CI run recompiled the SwiftPM dependencies from scratch. Cloning was never the cost -- compilation was. Cache the derived data Build directory so an unchanged dependency graph and toolchain reuse the compiled objects. The key is exact-match with no restore-keys, and records the resolved `xcodebuild -version` rather than the pinned label, so a toolchain bump rotates it instead of silently serving objects built by another compiler. Only Build and SourcePackages are cached; the index store is regenerated each run rather than restored, since an index unit outlives the source it was built from and the key cannot invalidate on a first-party source change. The SwiftPM download cache uses one identical path across every job. Its DerivedData glob matched nothing -- these jobs build with an explicit -derivedDataPath -- and a per-job path under one shared key would make GitHub store a separate near-identical entry per job. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01SRgQmnzeh3vsVKudXWs3RV
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Every CI run recompiled this app's SwiftPM dependencies from scratch. The existing SwiftPM cache covered only checkouts — and cloning was never the cost, compilation was.
Also fixes a cache that was silently doing nothing
The existing
Cache SwiftPM dependenciesstep globbed~/Library/Developer/Xcode/DerivedData/**/SourcePackages/checkouts, but these jobs build with an explicit-derivedDataPath. That glob matched nothing — the step was a no-op apart from the SwiftPM download cache.Key design
Exact-match, no
restore-keys— a partial restore of compiled objects across a changed dependency graph is how a stale-artifact bug gets in. The key records the resolvedxcodebuild -versionrather than the pinned label, so a toolchain bump rotates it instead of silently reusing objects built by a different compiler.Only
BuildandSourcePackagesare cached — notIndex.noindex. This matters for Periphery: an index unit outlives the source it was built from, and an exact-match key onPackage.resolvedcan't invalidate on a first-party source change, so a restored index could let Periphery read units for deleted or renamed files — a spurious--strictfailure or a silently missed finding.The SwiftPM download cache uses one identical path across every job. This is deliberate and was learned the hard way (see below).
A bug the canary caught
The first version gave each job its own
SourcePackages/checkoutspath under a shared key. GitHub derives a cache version from the path list, so identical keys with differing paths produce separate entries — five near-identical 1.2 GiB copies, duplicating content the build-product cache already held.Zephyrreached 10.57 GiB against GitHub's 10 GB per-repo limit, where eviction would have quietly undermined the caching this change exists to add. Now one shared entry per repo.Measured on the canary
Validated on
RISCfuture/Zephyr, cold then warm:The log confirms a 1201 MB derived-data restore followed by a successful warm build — so building on restored derived data is verified, not assumed.
Note
actionlintandyamllintclean. This PR's own run is a guaranteed cache miss.🤖 Generated with Claude Code
https://claude.ai/code/session_01SRgQmnzeh3vsVKudXWs3RV