patch 9.1.0550: filetype: antlr4 files are not recognized

Problem:  filetype: antlr4 files are not recognized
Solution: Detect '*.g4' as antlr4 filetype, include a simple antlr4
          syntax and filetype plugin (Yinzuo Jiang)

closes: #15191

Signed-off-by: Yinzuo Jiang <jiangyinzuo@foxmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

.github/MAINTAINERS

@@ -107,6 +107,7 @@ runtime/compiler/zsh.vim		@dkearns
 runtime/doc/ft_hare.txt			@selenebun
 runtime/doc/ps1.txt			@heaths
 runtime/ftplugin/abaqus.vim		@costerwi
+runtime/ftplugin/antlr4.vim		@jiangyinzuo
 runtime/ftplugin/apache.vim		@dubgeiser
 runtime/ftplugin/arduino.vim		@k-takata
 runtime/ftplugin/astro.vim		@romainl
@@ -368,6 +369,7 @@ runtime/syntax/shared/hgcommitDiff.vim	@vegerot
 runtime/syntax/abaqus.vim		@costerwi
 runtime/syntax/aidl.vim			@dpelle
 runtime/syntax/ant.vim			@dkearns
+runtime/syntax/antlr4.vim		@jiangyinzuo
 runtime/syntax/arduino.vim		@johshoff
 runtime/syntax/asciidoc.vim		@aerostitch
 runtime/syntax/asm.vim			@dkearns

runtime/filetype.vim

@@ -98,6 +98,13 @@ au BufNewFile,BufRead *.run			setf ampl
 " Ant
 au BufNewFile,BufRead build.xml			setf ant
 
+" ANTLR / PCCTS
+"au BufNewFile,BufRead *.g			setf antlr
+au BufNewFile,BufRead *.g			setf pccts
+
+" ANTLR 4
+au BufNewFile,BufRead *.g4			setf antlr4
+
 " Arduino
 au BufNewFile,BufRead *.ino,*.pde		setf arduino
 
@@ -1814,10 +1821,6 @@ au BufNewFile,BufRead *termcap
 " Prisma
 au BufRead,BufNewFile *.prisma			setf prisma
 
-" PCCTS / ANTLR
-"au BufNewFile,BufRead *.g			setf antlr
-au BufNewFile,BufRead *.g			setf pccts
-
 " PPWizard
 au BufNewFile,BufRead *.it,*.ih			setf ppwiz
 

runtime/ftplugin/antlr4.vim

@@ -0,0 +1,14 @@
+" Vim filetype plugin
+" Language:	ANTLR4, ANother Tool for Language Recognition v4 <www.antlr.org>
+" Maintainer:	Yinzuo Jiang <jiangyinzuo@foxmail.com>
+" Last Change:	2024 July 09
+
+if exists('b:did_ftplugin')
+  finish
+endif
+let b:did_ftplugin = 1
+
+setlocal comments=sO:*\ -,mO:*\ \ ,exO:*/,s1:/*,mb:*,ex:*/,://
+setlocal commentstring=//\ %s
+
+let b:undo_ftplugin = 'setl com< cms<'

runtime/syntax/antlr4.vim

@@ -0,0 +1,30 @@
+" Vim syntax file
+" Language:	ANTLR4, ANother Tool for Language Recognition v4 <www.antlr.org>
+" Maintainer:	Yinzuo Jiang <jiangyinzuo@foxmail.com>
+" Last Change:	2024 July 09
+
+" quit when a syntax file was already loaded
+if exists("b:current_syntax")
+  finish
+endif
+
+" Keywords. See https://github.com/antlr/antlr4/blob/4.13.1/doc/lexicon.md
+syn keyword antlr4Include import
+" https://github.com/antlr/antlr4/blob/4.13.1/doc/options.md
+" https://github.com/antlr/antlr4/blob/4.13.1/doc/grammars.md
+syn keyword antlr4Structure fragment lexer parser grammar options channels tokens mode
+syn keyword antlr4Statement returns locals
+syn keyword antlr4Exceptions throws catch finally
+
+" Comments.
+syn keyword antlr4Todo contained TODO FIXME XXX NOTE
+syn region antlr4Comment start="//"  end="$"   contains=antlr4Todo,@Spell
+syn region antlr4Comment start="/\*" end="\*/" contains=antlr4Todo,@Spell
+
+hi def link antlr4Include Include
+hi def link antlr4Structure Structure
+hi def link antlr4Statement Statement
+hi def link antlr4Exceptions Structure
+hi def link antlr4Comment Comment
+
+let b:current_syntax = "antlr4"

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    550,
 /**/
     549,
 /**/