bug#37133: 27.0.50; use Autoconf mode instead of m4 for acinclude.m4, aclocal.m4 and acsite.m4

[Lars Ingebrigtsen <larsi@mouse.gnus.org>]

Vincent Lefevre <vincent@vinc17.net> writes:

> By default, the m4 mode is used for the acinclude.m4, aclocal.m4 and
> acsite.m4 files. It would be better to use the more specific Autoconf
> mode for these files (like configure.ac).

I don't know these modes well, but the doc string for `autoconf-mode'
says:

---
Major mode for editing Autoconf configure.ac files.
---

So would using it for these other .m4 files be appropriate?  If it is,
the following patch would fix the problem.

diff --git a/lisp/files.el b/lisp/files.el
index f76635017d..2a84c2c48f 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2719,6 +2719,8 @@ auto-mode-alist
      ("\\.bib\\'" . bibtex-mode)
      ("\\.bst\\'" . bibtex-style-mode)
      ("\\.sql\\'" . sql-mode)
+     ;; These .m4 files are Autoconf files.
+     ("\\(acinclude\\|aclocal\\|acsite\\)\\.m4\\'" . autoconf-mode)
      ("\\.m[4c]\\'" . m4-mode)
      ("\\.mf\\'" . metafont-mode)
      ("\\.mp\\'" . metapost-mode)


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   bloggy blog: http://lars.ingebrigtsen.no