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From:   Masahiro Yamada <masahiroy@kernel.org>
Date:   Thu, 12 Jan 2023 13:35:08 +0900
Message-ID: <CAK7LNASDu+i4G88TYYa6feg-bha-_cLv1si_ujuSMbWuyUve0Q@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 Thu, Jan 12, 2023 at 1:33 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> 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
>


I meant this:


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


(">/dev/null" was lost in the previous email)


-- 
Best Regards
Masahiro Yamada