[bug#28787] [PATCH 1/2] emacs-build-system: Handle missing programs when patching.

[ludo@gnu.org (Ludovic Courtès)]

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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:


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diff --git a/guix/build/emacs-build-system.scm b/guix/build/emacs-build-system.scm
index 2404dbddb..bafb1060b 100644
--- a/guix/build/emacs-build-system.scm
+++ b/guix/build/emacs-build-system.scm
@@ -93,7 +93,10 @@ store in '.el' files."
          (substitute-cmd (lambda ()
                            (substitute* (find-files "." "\\.el$")
                              (("\"/bin/([^.].*)\"" _ cmd)
-                              (string-append "\"" (which cmd) "\""))))))
+                              (let ((cmd (which cmd)))
+                                (unless cmd
+                                  (error "..."))
+                                (string-append "\"" cmd "\"")))))))
     (with-directory-excursion el-dir
       ;; Some old '.el' files (e.g., tex-buf.el in AUCTeX) are still encoded
       ;; with the "ISO-8859-1" locale.

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Otherwise LGTM!

Thanks,
Ludo’.