Re: [PATCH v2 05/11] kbuild: rust_is_available: add check for `bindgen` invocation

[Nathan Chancellor]

On Fri, Jun 16, 2023 at 02:16:25AM +0200, Miguel Ojeda 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@xxxxxxxxxx>
> Link: https://lore.kernel.org/rust-for-linux/CAKwvOdm5JT4wbdQQYuW+RT07rCi6whGBM2iUAyg8A1CmLXG6Nw@xxxxxxxxxxxxxx/
> Reported-by: François Valenduc <francoisvalenduc@xxxxxxxxx>
> Closes: https://github.com/Rust-for-Linux/linux/issues/934
> Reported-by: Alexandru Radovici <msg4alex@xxxxxxxxx>
> Closes: https://github.com/Rust-for-Linux/linux/pull/921
> Reported-by: Matthew Leach <dev@xxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/rust-for-linux/20230507084116.1099067-1-dev@xxxxxxxxxxxxx/
> Fixes: 78521f3399ab ("scripts: add `rust_is_available.sh`")
> Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>

Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>

> ---
>  scripts/rust_is_available.sh | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/rust_is_available.sh b/scripts/rust_is_available.sh
> index 6b8131d5b547..1bdff4472cbe 100755
> --- a/scripts/rust_is_available.sh
> +++ b/scripts/rust_is_available.sh
> @@ -106,8 +106,28 @@ 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.
> +bindgen_libclang_output=$( \
> +	LC_ALL=C "$BINDGEN" $(dirname $0)/rust_is_available_bindgen_libclang.h 2>&1 >/dev/null
> +) || bindgen_libclang_code=$?
> +if [ -n "$bindgen_libclang_code" ]; then
> +	echo >&2 "***"
> +	echo >&2 "*** Running '$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
> +
> +# `bindgen` returned successfully, thus use the output to check that the version
> +# of the `libclang` found by the Rust bindings generator is suitable.
>  bindgen_libclang_version=$( \
> -	LC_ALL=C "$BINDGEN" $(dirname $0)/rust_is_available_bindgen_libclang.h 2>&1 >/dev/null \
> +	echo "$bindgen_libclang_output" \
>  		| grep -F 'clang version ' \
>  		| grep -oE '[0-9]+\.[0-9]+\.[0-9]+' \
>  		| head -n 1 \
> -- 
> 2.41.0
>