Commit: runtime(m4): Improve comments, distinguish them from #-lines

[Christian Brabandt]

runtime(m4): Improve comments, distinguish them from #-lines

Commit: https://github.com/vim/vim/commit/510ca80c58088276d8b1744a729f69d34c550566
Author: Damien Lejay <dam...@lejay.be>
Date: Fri Sep 5 17:48:39 2025 +0200

runtime(m4): Improve comments, distinguish them from #-lines

closes: https://github.com/vim/vim/issues/18200

Signed-off-by: Damien Lejay <dam...@lejay.be>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/runtime/syntax/m4.vim b/runtime/syntax/m4.vim
index 7520e65d9..9d5116087 100644
--- a/runtime/syntax/m4.vim
+++ b/runtime/syntax/m4.vim
@@ -3,6 +3,7 @@
" Maintainer: Claudio Fleiner (cla...@fleiner.com)
" Last Change: 2022 Jun 12
" 2025 Sep 2 by Vim project: fix a few syntax issues #18192
+" 2025 Sep 5 by Vim project: introduce m4Disabled region #18200

" This file will highlight user function calls if they use only
" capital letters and have at least one argument (i.e. the '('
@@ -24,7 +25,7 @@ endif
" – Quotes are nestable;
" – The delimiters can be redefined with changequote(); here we only handle
" the default pair: ` ... ';
-" – Quoted text in M4 is rescanned, not treated as a literal string;
+" – Quoted text in M4 is rescanned, not treated as a literal string.
" Therefore the region is marked transparent so contained items retain
" their normal highlighting.
syn region m4Quoted
@@ -34,11 +35,20 @@ syn region m4Quoted
\ contains=@m4Top
\ transparent

+" Comments in M4:
+" – According to the Open Group Base Specification, comments start with
+" a <number-sign> (#) and end at <newline>, unless redefined with changecom().
+" We only handle the default here.
+" – Comments in M4 are not like in most languages: they do not remove the text,
+" they simply prevent any macros from being expanded, while the text remains
+" in the output. This region therefore disables any other matches.
+" – Comments themselves are disabled when quoted.
+syn region m4Disabled start=+#+ end=+$+ containedin=ALLBUT,m4Quoted
+
" define the m4 syntax
syn match m4Variable contained "\$\d\+"
syn match m4Special contained "$[@*#]"
syn match m4Comment "\<\(m4_\)\=dnl\>.*" contains=SpellErrors
-syn match m4Comment "#.*" contains=SpellErrors
syn match m4Constants "\<\(m4_\)\=__file__"
syn match m4Constants "\<\(m4_\)\=__line__"
syn keyword m4Constants divnum sysval m4_divnum m4_sysval