Commit: runtime(m4): Improve parameters highlighting in syntax script

[Christian Brabandt]

runtime(m4): Improve parameters highlighting in syntax script

Commit: https://github.com/vim/vim/commit/8801c9db2e8e5da90b2e52ceacfd726543d12407
Author: Damien Lejay <dam...@lejay.be>
Date: Mon Sep 15 19:59:58 2025 +0000

runtime(m4): Improve parameters highlighting in syntax script

closes: https://github.com/vim/vim/issues/18306

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 5100b4c3a..c993e5864 100644
--- a/runtime/syntax/m4.vim
+++ b/runtime/syntax/m4.vim
@@ -6,6 +6,7 @@
" 2025 Sep 5 by Vim project: introduce m4Disabled region #18200
" 2025 Sep 6 by Vim project: remove m4Function heuristics #18211
" 2025 Sep 6 by Vim project: remove m4Type and m4Function #18223
+" 2025 Sep 15 by Vim project: highlight m4Parameters #18306

" quit when a syntax file was already loaded
if !exists("main_syntax")
@@ -19,6 +20,9 @@ endif
" Reference: The Open Group Base Specifications, M4
" https://pubs.opengroup.org/onlinepubs/9799919799/

+" Early definition of a cluster
+syn cluster m4Top contains=NONE
+
" Quoting in M4:
" – Quotes are nestable;
" – The delimiters can be redefined with changequote(); here we only handle
@@ -32,6 +36,7 @@ syn region m4Quoted
\ end=+'+
\ contains=@m4Top
\ transparent
+syn cluster m4Top add=m4Quoted

" Comments in M4:
" – According to the Open Group Base Specification, comments start with
@@ -41,7 +46,7 @@ syn region m4Quoted
" 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=+$+ containedin=ALLBUT,m4Quoted
+syn region m4Disabled start=+#+ end=+$+ containedin=ALLBUT,m4Quoted,m4ParamCount

" Macros in M4:
" – Name tokens consist of the longest possible sequence of letters, digits,
@@ -50,9 +55,17 @@ syn region m4Disabled start=+#+ end=+$+ containedin=ALLBUT,m4Quoted
" – Any name token may be defined as a macro and quoting prevents expansion.
" Thus correct highlighting requires running M4.

-" define the m4 syntax
-syn match m4Variable contained "\$\d\+"
-syn match m4Special contained "$[@*#]"
+" Parameters in M4:
+" $0 = macro name; $1..$9 = positional (single digit only); $# = count;
+" $* = args comma-joined; $@ = args quoted+comma; "${" = unspecified.
+syn match m4ParamZero contained "\$0"
+syn match m4ParamPos contained "\$[1-9]"
+syn match m4ParamCount contained "\$#"
+syn match m4ParamAll contained "\$[@*]"
+syn match m4ParamBad contained '\${'
+syn cluster m4Top add=m4ParamZero,m4ParamPos,m4ParamCount,m4ParamAll,m4ParamBad
+
+" define the rest of M4 syntax
syn match m4Comment "\<\(m4_\)\=dnl\>.*" contains=SpellErrors
syn match m4Constants "\<\(m4_\)\=__file__"
syn match m4Constants "\<\(m4_\)\=__line__"
@@ -64,19 +77,22 @@ syn region m4Command matchgroup=m4Statement start="\<\(m4_\)\=\(syscmd\|esyscmd
syn region m4Command matchgroup=m4Builtin start="\<\(m4_\)\=\(len\|index\|regexp\|substr\|translit\|patsubst\|format\|incr\|decr\|eval\|maketemp\)("he=e-1 end=")" contains=@m4Top
syn keyword m4Statement divert undivert
syn region m4Command matchgroup=m4Define start="\<\(m4_\)\=\(undefine\|popdef\)("he=e-1 end=")" contains=@m4Top
-syn cluster m4Top contains=m4Comment,m4Constants,m4Special,m4Variable,m4Paren,m4Command,m4Statement,m4Quoted
+syn cluster m4Top add=m4Comment,m4Constants,m4Paren,m4Command,m4Statement

" Define the default highlighting.
" Only when an item doesn't have highlighting yet
hi def link m4QuoteDelim Delimiter
hi def link m4Delimiter Delimiter
hi def link m4Comment Comment
+hi def link m4ParamZero Macro
+hi def link m4ParamPos Special
+hi def link m4ParamCount Keyword
+hi def link m4ParamAll Keyword
+hi def link m4ParamBad Error
hi def link m4Keyword Keyword
hi def link m4Define Define
-hi def link m4Special Special
hi def link m4Statement Statement
hi def link m4Preproc PreProc
-hi def link m4Variable Special
hi def link m4Constants Constant
hi def link m4Builtin Statement