[bug#57122] [PATCH] build-system: emacs: Use new function for autoloads generation

[Morgan . J . Smith]

From: Morgan Smith <Morgan.J.Smith@outlook.com>

* guix/build/emacs-utils.scm (emacs-generate-autoloads): Use
'loaddefs-generate' to create autoloads instead of
'update-directory-autoloads' if we are using a new enough Emacs
---

I'm not sure how long it takes to rebuild all the Emacs packages so I CC'd 
Liliana since they are going to change the Emacs build system soon anyways.

This change is to allow packages to be built with the latest commits of emacs 
(guix build emacs-crdt --with-input=emacs-minimal=emacs-next 
--with-latest=emacs-next)

Just last week the 'update-directory-autoloads' function got deprecated and 
replaced.  Since continuing to use the deprecated function would require 
changes anyways (adding a '(require 'autoloads)' would do it I think), I 
decided to just use the newer function.

Is this a bug in upstream Emacs where autoloaded functions like 
'update-directory-autoloads' don't get autoloaded when they are in the obsolete 
directory?  Possibly.  Is this a bug related to our packaging of Emacs?  
Possibly.  Is this the intended behaviour?  Possibly.  I'm not the guy to ask 
:P. I'm really not sure why this stopped working.  But we will have to switch 
to the 'loaddefs-generate' function eventually anyways so I think this patch is 
probably good to apply.


Thanks,

Morgan


 guix/build/emacs-utils.scm | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/guix/build/emacs-utils.scm b/guix/build/emacs-utils.scm
index 8ee547f2b3..180c3ae08c 100644
--- a/guix/build/emacs-utils.scm
+++ b/guix/build/emacs-utils.scm
@@ -105,7 +105,11 @@ (define (emacs-generate-autoloads name directory)
   (let* ((file (string-append directory "/" name "-autoloads.el"))
          (expr `(let ((backup-inhibited t)
                       (generated-autoload-file ,file))
-                  (update-directory-autoloads ,directory))))
+                  (if (not (require 'loaddefs-gen nil t))
+                      ;; Emacs <= 28
+                      (update-directory-autoloads ,directory)
+                    ;; Emacs >= 29
+                    (loaddefs-generate ,directory ,file)))))
     (emacs-batch-eval expr #:dynamic? #t)))
 
 (define* (emacs-byte-compile-directory dir)
-- 
2.37.1