Please stop using GITHUB_ACTION to change the behaviour of the build system

[lu-zero]

It causes surprising breakages openwrt/packages#26623 downstream.

If we can agree to use an env var like RUST_CI_IN_USE I'll prepare a patch.

[onur-ozkan]

There is no need to introduce another ENV. You can prepare a patch that uses is_rust_lang_managed_ci_job instead of is_ci for cases where you think using GITHUB_ACTIONS doesn't make sense.

[bjorn3]

download-ci-llvm is only meant for local development. If you use it in CI, your CI will break in a couple of months unless you regularly update rustc. The per-commit CI artifacts that download-ci-llvm downloads only get retained for a limited amount of time.

[workingjubilee]

We should straight-up advise setting download-ci-llvm = false.

[onur-ozkan]

We should straight-up advise setting download-ci-llvm = false.

#141782 🤷

[workingjubilee]

Yes, that's because @lu-zero set it in the package file, so @smallprogram doesn't feel empowered to change it because they're not the maintainer of the package.

[onur-ozkan]

We should straight-up advise setting download-ci-llvm = false.

Alternatively, if they don't want to compile LLVM for some reason and prefer to use a precompiled version, there is a better way. They can specify the path to llvm-config like this:

[target.x86_64-unknown-linux-gnu]
llvm-config = "/path/to/llvm-config"

Maybe we should include this in the error message.

[bjorn3]

We should straight-up advise setting download-ci-llvm = false.

We could also forcefully set download-ci-llvm to false if the current channel is not dev or nightly.