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References: <20230109204520.539080-1-ojeda@kernel.org> <20230109204520.539080-3-ojeda@kernel.org>
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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Thu, 12 Jan 2023 13:33:09 +0900
Message-ID: <CAK7LNATVJ5e=DnbJ++03iEMk0bN3-UvODBLkEKcYdSnJZa_tmA@mail.gmail.com>
Subject: Re: [PATCH 3/6] kbuild: rust_is_available: add check for `bindgen` invocation
To:     Miguel Ojeda <ojeda@kernel.org>
Cc:     linux-kbuild@vger.kernel.org,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Schier <nicolas@fjasle.eu>,
        rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org,
        patches@lists.linux.dev, Alexandru Radovici <msg4alex@gmail.com>,
        Alex Gaynor <alex.gaynor@gmail.com>,
        Wedson Almeida Filho <wedsonaf@gmail.com>,
        Boqun Feng <boqun.feng@gmail.com>, Gary Guo <gary@garyguo.net>,
        =?UTF-8?Q?Bj=C3=B6rn_Roy_Baron?= <bjorn3_gh@protonmail.com>
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On Tue, Jan 10, 2023 at 5:45 AM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> `scripts/rust_is_available.sh` calls `bindgen` with a special
> header in order to check whether the `libclang` version in use
> is suitable.
>
> However, the invocation itself may fail if, for instance, `bindgen`
> cannot locate `libclang`. This is fine for Kconfig (since the
> script will still fail and therefore disable Rust as it should),
> but it is pretty confusing for users of the `rustavailable` target
> given the error will be unrelated:
>
>     ./scripts/rust_is_available.sh: 21: arithmetic expression: expecting primary: "100000 *  + 100 *  + "
>     make: *** [Makefile:1816: rustavailable] Error 2
>
> Instead, run the `bindgen` invocation independently in a previous
> step, saving its output and return code. If it fails, then show
> the user a proper error message. Otherwise, continue as usual
> with the saved output.
>
> Since the previous patch we show a reference to the docs, and
> the docs now explain how `bindgen` looks for `libclang`,
> thus the error message can leverage the documentation, avoiding
> duplication here (and making users aware of the setup guide in
> the documentation).
>
> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
> Reported-by: fvalenduc (@fvalenduc)
> Reported-by: Alexandru Radovici <msg4alex@gmail.com>
> Link: https://lore.kernel.org/rust-for-linux/CAKwvOdm5JT4wbdQQYuW+RT07rCi6whGBM2iUAyg8A1CmLXG6Nw@mail.gmail.com/
> Link: https://github.com/Rust-for-Linux/linux/issues/934
> Link: https://github.com/Rust-for-Linux/linux/pull/921
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
>  scripts/rust_is_available.sh | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/rust_is_available.sh b/scripts/rust_is_available.sh
> index c907cf881c2c..cd87729ca3bf 100755
> --- a/scripts/rust_is_available.sh
> +++ b/scripts/rust_is_available.sh
> @@ -108,8 +108,29 @@ if [ "$rust_bindings_generator_cversion" -gt "$rust_bindings_generator_min_cvers
>  fi
>
>  # Check that the `libclang` used by the Rust bindings generator is suitable.
> +#
> +# In order to do that, first invoke `bindgen` to get the `libclang` version
> +# found by `bindgen`. This step may already fail if, for instance, `libclang`
> +# is not found, thus inform the user in such a case.
> +set +e
> +bindgen_libclang_output=$(LC_ALL=C "$BINDGEN" $(dirname $0)/rust_is_available_bindgen_libclang.h 2>&1 >/dev/null)
> +bindgen_libclang_code=$?
> +set -e
> +if [ $bindgen_libclang_code -ne 0 ]; then
> +       echo >&2 "***"
> +       echo >&2 "*** Running '$BINDGEN' to check the libclang version (used by the Rust"
> +       echo >&2 "*** bindings generator) failed with code $bindgen_libclang_code. This may be caused by"
> +       echo >&2 "*** a failure to locate libclang. See output and docs below for details:"
> +       echo >&2 "***"
> +       echo >&2 "$bindgen_libclang_output"
> +       echo >&2 "***"
> +       exit 1
> +fi
>


Instead of toggling -e, why don't you write like this?


if ! bindgen_libclang_output=$(LC_ALL=C "$BINDGEN" $(dirname
$0)/rust_is_available_bindgen_libclang.h 2>&1); then
       [snip]
fi


--
Best Regards
Masahiro Yamada