Hello!

Christopher Baines <mail@cbaines.net> skribis:

> Previously the string-append here would error, which isn't useful as it
> doesn't tell you which command couldn't be found. To make the error
> actionable, catch it earlier, and explicitly error.
>
> * guix/build/emacs-build-system.scm (patch-el-files): Handle (which cmd)
>   returning #f.
> ---
>  guix/build/emacs-build-system.scm | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/guix/build/emacs-build-system.scm b/guix/build/emacs-build-system.scm
> index 2404dbddb..0260f15bb 100644
> --- a/guix/build/emacs-build-system.scm
> +++ b/guix/build/emacs-build-system.scm
> @@ -93,7 +93,12 @@ store in '.el' files."
>           (substitute-cmd (lambda ()
>                             (substitute* (find-files "." "\\.el$")
>                               (("\"/bin/([^.].*)\"" _ cmd)
> -                              (string-append "\"" (which cmd) "\""))))))
> +                              (string-append
> +                               "\""
> +                               (or
> +                                (which cmd)
> +                                (error "patch-el-files: unable to locate " cmd))
> +                               "\""))))))

For clarity I’d move the ‘error’ call out of the way: