01/02: emacs-build-system: Handle missing programs when patching.

[Christopher Baines]

cbaines pushed a commit to branch master
in repository guix.

commit dd2de2842344ede8e92459fe66c5a45ca3dc40ff
Author: Christopher Baines <address@hidden>
Date:   Wed Oct 11 11:59:20 2017 +0100

    emacs-build-system: Handle missing programs when patching.
    
    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 | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/guix/build/emacs-build-system.scm 
b/guix/build/emacs-build-system.scm
index 2404dbd..1474c80 100644
--- a/guix/build/emacs-build-system.scm
+++ b/guix/build/emacs-build-system.scm
@@ -92,8 +92,12 @@ store in '.el' files."
          (el-dir (string-append out %install-suffix "/" elpa-name-ver))
          (substitute-cmd (lambda ()
                            (substitute* (find-files "." "\\.el$")
-                             (("\"/bin/([^.].*)\"" _ cmd)
-                              (string-append "\"" (which cmd) "\""))))))
+                             (("\"/bin/([^.].*)\"" _ cmd-name)
+                              (let ((cmd (which cmd-name)))
+                                (unless cmd
+                                  (error
+                                   "patch-el-files: unable to locate " 
cmd-name))
+                                (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.