[shubh73]

If fileMapCacheDirectory points at a directory that doesn't exist yet, the file map cache is never written, so every restart crawls the project from scratch. The only sign is a warning at startup:

[metro-file-map] Cache write error
: Error: ENOENT: no such file or directory, open '/path/to/project/node_modules/.cache/metro-file-map/metro-file-map-<hash>-<hash>'

The default, os.tmpdir(), always exists, so this only affects a custom directory - but a project-local one like node_modules/.cache/metro-file-map won't exist on a fresh checkout or after node_modules is removed. The transform cache doesn't have this problem, because FileStore creates its directory when a write fails with ENOENT.

This change does the same in DiskCacheManager: on ENOENT, create the directory (recursively) and retry the write once. Writes into an existing directory are unchanged.

Note

Found in an Expo SDK 57 app. Expo CLI uses its fork, @expo/metro-file-map, which has the same writeFile in DiskCacheManager.ts, so it'll need the same change.

Changelog:

 - **[Fix]**: Create `fileMapCacheDirectory` if it doesn't exist, rather than failing to persist the file map cache

Test plan:
New test in DiskCacheManager-test.js where the first write fails with ENOENT, asserting that the directory is created and the snapshot written without an error. It fails before this change and passes after. A second test checks that other errors, e.g. EACCES, are still reported without a retry.

Also checked end-to-end with createFileMap and fileMapCacheDirectory set to a missing <project>/node_modules/.cache/metro-file-map: before, the warning above and no directory; after, no warning and the cache file is written.

yarn jest packages/metro-file-map packages/metro/src/node-haste packages/metro/src/DeltaBundler
yarn flow check
yarn eslint packages/metro-file-map
yarn verify-api-snapshots

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