Re: [PATCH 4/6] kbuild: rust_is_available: check if the script was invoked from Kbuild

[Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>]

On Thu, Jan 12, 2023 at 6:29 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> I do not like this.
> We do not need to cater to every oddity.
>
> Checking MAKEFLAGS is too much.

I agree we should not attempt to catch every possible mistake in the
script, but there have been several people hitting precisely this case
(the latest is in the linked thread in the commit message), i.e. some
people read the `Makefile` and notice the script invocation, and go
execute it, but they are unlikely to be aware of the target in that
case.

> You can check RUSTC/BINDGEN/CC if you persist in this.

This is fine, and actually we should do it regardless of `MAKEFLAGS`.
I can add it to v2.

However, that does not cover the same thing as `MAKEFLAGS` is trying
to here. The reason is that even if they see e.g. "RUSTC is not set",
they will not know about how to call the script properly, i.e. through
the `Makefile` target.

For `RUSTC` and `BINDGEN`, it does not really matter (and we could
give a default to the variable, since the name rarely would be
different). However, for `CC`, the logic that Kbuild uses is more
complex, so it seems best to me to let Kbuild tell us what the actual
compiler is.

Cheers,
Miguel