Howdy all,

currently, --action_env is affecting environment variables for Bazel actions, but also the environment for repository rules. Because of that it is possible to run Bazel as bazel build --action_env=CC=/usr/bin/clang //... when the user means CC=/usr/bin/clang bazel build //.... Using --action_env is tempting, since it can be put into .bazelrc file and be a part of configs there, allowing you to have single flag build, e.g. bazel build --config=cuda //....

The problem with that is that changing --action_env invalidates entire action graph when a environment variable changes, even though only one repository rule depended on the variable, it's output was the same, and change didn't need to be propagated further.

I assume there are multiple possible solutions, my first guess would be to add a --repo_env Bazel option that only affected repository rules and not actions, but I'll leave this to experts.

I'll also try to generalize the problem a bit - we don't need environment variables specifically, it's just the current way how to configure repository rules. Therefore I'm asking for a way to configure repository rules from Bazel options.