Persist Metro transform and file-map caches under .harness#160
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Introduce @react-native-harness/cache as the single owner of .harness/cache layout and warmth checks. Metro's transform cache moves to .harness/cache/metro and its file-map (haste) cache, previously left in $TMPDIR, is now pinned to .harness/cache/metro-file-map. Both are enabled by default via a new `cache` config option group; `unstable__enableMetroCache` is kept as a deprecated alias for one release. The GitHub Action's cache step now covers both directories under a bumped cache key.
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What is this?
Metro's transform cache and its file-map (haste) cache now persist under
.harness/cache/metroand.harness/cache/metro-file-mapin your project root, on by default. Previously, persistent caching required opting in (unstable__enableMetroCache), and even then only the transform cache was captured — the file-map cache always fell back to a temp directory and was invisible to CI caching.How does it work?
A new package,
@react-native-harness/cache, owns the.harness/cachelayout and warmth checks; it's the single place that constructs cache paths, so Metro integration, Jest, and future cache domains all consume its narrow API instead of duplicating path logic. Caching is controlled by a newcacheconfig option group (cache.metro, defaulting totrue;cache.versionas an invalidation salt folded into Metro'scacheVersion, which is now derived from the package version instead of a static string). The previousunstable__enableMetroCacheflag still works as a deprecated alias for one release. Cache I/O never fails a run — any filesystem error while creating directories or checking warmth is logged and treated as a cold cache. The GitHub Action's Metro cache step now restores/saves both directories under a bumped cache key so old entries at the previous location aren't mistakenly reused.Why is this useful?
Repeated Metro runs, both locally and in CI, no longer discard the file-map crawl and transform work between invocations by default. Consolidating everything under
.harness/cachealso gives the project a single directory to reason about, back up, or wipe, and sets up a stable component boundary for caching other things (the iOS XCTest agent build, Android AVDs) in a follow-up change.