linux-kernel - Re: [PATCH v2 06/11] kbuild: rust_is_available: check that environment variables are set

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Date:   Tue, 20 Jun 2023 13:59:17 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     Wedson Almeida Filho <wedsonaf@...il.com>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Andreas Hindborg <nmi@...aspace.dk>,
        linux-kbuild@...r.kernel.org, rust-for-linux@...r.kernel.org,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH v2 06/11] kbuild: rust_is_available: check that
 environment variables are set

On Fri, Jun 16, 2023 at 9:17 AM Miguel Ojeda <ojeda@...nel.org> wrote:
>
> Sometimes [1] users may attempt to setup the Rust support by
> checking what Kbuild does and they end up finding out about
> `scripts/rust_is_available.sh`. Inevitably, they run the script
> directly, but unless they setup the required variables,
> the result of the script is not meaningful.
>
> We could add some defaults to the variables, but that could be
> confusing for those that may override the defaults (compared
> to their kernel builds), and `$CC` would not be a simple default
> in any case.
>
> Therefore, instead, explicitly check whether the expected variables
> are set (`$RUSTC`, `$BINDGEN` and `$CC`). If not, print an explanation
> about the fact that the script is meant to be called from Kbuild,
> since that is the most likely cause for the variables not being set.
>
> Link: https://lore.kernel.org/oe-kbuild-all/Y6r4mXz5NS0+HVXo@zn.tnic/ [1]
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
>  scripts/rust_is_available.sh | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/scripts/rust_is_available.sh b/scripts/rust_is_available.sh
> index 1bdff4472cbe..7e0368babe64 100755
> --- a/scripts/rust_is_available.sh
> +++ b/scripts/rust_is_available.sh
> @@ -28,11 +28,40 @@ print_docs_reference()
>         echo >&2 "***"
>  }
>
> +# Print an explanation about the fact that the script is meant to be called from Kbuild.
> +print_kbuild_explanation()
> +{
> +       echo >&2 "***"
> +       echo >&2 "*** This script is intended to be called from Kbuild."
> +       echo >&2 "*** Please use the 'rustavailable' target to call it instead."
> +       echo >&2 "*** Otherwise, the results may not be meaningful."
> +       exit 1
> +}
> +
>  # If the script fails for any reason, or if there was any warning, then
>  # print a reference to the documentation on exit.
>  warning=0
>  trap 'if [ $? -ne 0 ] || [ $warning -ne 0 ]; then print_docs_reference; fi' EXIT
>
> +# Check that the expected environment variables are set.
> +if [ -z "${RUSTC+x}" ]; then
> +       echo >&2 "***"
> +       echo >&2 "*** Environment variable 'RUSTC' is not set."
> +       print_kbuild_explanation
> +fi


So, you want to check whether RUSTC is set or unset.
(that is, you allow a case where RUSTC is set, but empty.
It will eventually fail with a different error message anyway.)




$ ./scripts/rust_is_available.sh
***
*** Environment variable 'RUSTC' is not set.
***
*** This script is intended to be called from Kbuild.
*** Please use the 'rustavailable' target to call it instead.
*** Otherwise, the results may not be meaningful.
***
*** Please see Documentation/rust/quick-start.rst for details
*** on how to set up the Rust support.
***

$ RUSTC= BINDGEN= CC= ./scripts/rust_is_available.sh
***
*** Rust compiler '' could not be found.
***
***
*** Please see Documentation/rust/quick-start.rst for details
*** on how to set up the Rust support.
***



I would rather check whether RUSTC is empty or not
with simpler code.


if [ -z "${RUSTC}" ]; then
         ...
fi





> +
> +if [ -z "${BINDGEN+x}" ]; then
> +       echo >&2 "***"
> +       echo >&2 "*** Environment variable 'BINDGEN' is not set."
> +       print_kbuild_explanation
> +fi
> +
> +if [ -z "${CC+x}" ]; then
> +       echo >&2 "***"
> +       echo >&2 "*** Environment variable 'CC' is not set."
> +       print_kbuild_explanation
> +fi
> +
>  # Check that the Rust compiler exists.
>  if ! command -v "$RUSTC" >/dev/null; then
>         echo >&2 "***"
> --
> 2.41.0
>


-- 
Best Regards
Masahiro Yamada