In a quest to speed up Bazel builds we tend to pick every available low-hanging fruit once somebody discovers it. One of those used to be telling Bazel not to check external repos for file changes, since that can take a while in a dependency-heavy repo.

Prior Art

Historically we used --noexperimental_check_external_repository_files to skip checks for files in external repositories. That flag still exists in Bazel (source), and bazelrc-preset.bzl still sets it (source).

Bazel 9 gained the repo contents cache via --repo_contents_cache. Cacheable external repos can now be served out of that cache.

That matters because Bazel does not treat repo-contents-cache-backed files as the old EXTERNAL_REPO case. In the source they are tracked as EXTERNAL_OTHER instead. Bazel 9 also added --experimental_check_external_other_files to control checks for those paths..

Conclusion

If you have repo contents cache enabled and your goal is the old “don’t spend time stat’ing external repos on no-op builds” behavior, you likely want both:

• --noexperimental_check_external_repository_files
• --experimental_check_external_other_files=false

The old flag still matters for repos that are not served out of the repo contents cache. The new flag matters for cache-backed repos.

If repo contents cache is disabled, --experimental_check_external_other_files=false can still help with those broader EXTERNAL_OTHER checks, but it does not replace the old external-repository flag.