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

[Nathan Chancellor <nathan@kernel.org>]

On Fri, Jun 16, 2023 at 02:16:26AM +0200, Miguel Ojeda 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@kernel.org>

Reviewed-by: Nathan Chancellor <nathan@kernel.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
> +
> +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
>