Bazel 9 migration

[meteorcloudy]

Bazel 9 is shipping!
https://blog.bazel.build/2026/01/20/bazel-9.html

To help everyone transition smoothly, we’re using this discussion to centralize migration issues & solutions.

If you encounter a breaking change that's not obvious to fix during your upgrade, please post it here and share your solution if you already fixed it. The Bazel team and the community are also ready to help troubleshoot and find solutions!

Note: For core bugs, please open a GitHub Issue. For general release notes, please check the Bazel 9 release notes.

[meteorcloudy]

The flag --incompatible_autoload_externally now defaults to the empty string, meaning that all language-specific rules will now need to be loaded from their respective modules (rules_cc, rules_java, etc).

You can fix your BUILD or bzl file with:

buildifier --lint=fix <path-to-BUILD-or-bzl-file>

or all files at once

buildifier --lint=fix -r ./

You'll also need to fix and upgrade your dependencies that are missing the load statements.

[meteorcloudy]

We have managed to flip --incompatible_strict_action_env for better hermetically.

If your build or test action cannot find some binary with Bazel 9, it might be due to this. You can often work around via --action_env=PATH or --test_env=PATH, but it's also worth making your action more hermetic.