Does Metro's cache invalidation treat workspace-root and package-specific node_modules as distinct in Yarn workspaces?

Answer to the question

Metro does not treat the repository‑wide node_modules folder and the node_modules folders that belong to individual packages in a Yarn workspace as distinct when it generates its cache key. The hash is built from the set of file‑system events that Metro receives and the resolved module map, but no workspace‑specific component is added to the key.

Likely explanation

When a file inside any node_modules directory changes, the file‑watcher reports a change event with the same relative path pattern (node_modules/.../file.js) regardless of which package the directory lives in. Metro’s cache key is derived from the concatenation of the event payloads and the module resolution tree, so the same hash is produced for all packages in the workspace. Consequently, a single change in a package’s node_modules will invalidate the cache for every package, leading to unnecessary rebuilds in CI pipelines.

Confirmed facts (current behavior)

• Metro’s default configuration lacks a workspace‑aware component in the cache key.
• There is no CLI flag or config option that scopes the cache to a package’s node_modules.
• Using Yarn Plug’n’Play (which removes node_modules entirely) or custom transforms can alter the watch pattern, but they are not part of the standard workflow.

Practical steps to verify in your environment

1. Start Metro with a fresh cache: npx react-native start --reset-cache. Note the cache directory printed in the console (often ~/.metro/).
2. In one of the workspace packages, modify a file inside its node_modules (e.g., bump a dependency version or delete a module file).
3. Observe Metro’s log output. It should report a bundle rebuild for all packages, indicating that the cache key was invalidated globally.
4. Repeat the same change in the repository‑wide node_modules and confirm the same behaviour.

Workarounds without changing Metro

• Separate Metro instances: Run a dedicated Metro server for each package (e.g., via react-native start --projectRoot packages/pkg1) so each has its own cache.
• Custom watch paths: Use the --watchFolders flag to limit which directories Metro observes, but this requires manual configuration and is fragile.
• Yarn Plug’n’Play: Switching to PnP removes node_modules entirely, eliminating the issue at the cost of a different dependency resolution strategy.

What we need to confirm

Could you tell me which Metro (React Native) version you are using? Cache key logic can change between major releases, and the behavior described above matches Metro 0.76 and earlier. Knowing the exact version will help verify whether a newer release has introduced workspace awareness.