patch 9.1.0995: filetype: shaderslang files are not detected

Problem:  filetype: shaderslang files are not detected
Solution: detect '*.slang' files as shaderslang filetype,
          include a filetype and syntax script (mtvare6)

Reference:
https://shader-slang.com/

closes: #16387

Signed-off-by: mtvare6 <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: mTvare6

.github/MAINTAINERS

@@ -273,6 +273,7 @@ runtime/ftplugin/scss.vim		@tpope
 runtime/ftplugin/sdoc.vim		@gpanders
 runtime/ftplugin/sed.vim		@dkearns
 runtime/ftplugin/sh.vim			@dkearns
+runtime/ftplugin/shaderslang.vim        @mTvare6
 runtime/ftplugin/slint.vim		@ribru17
 runtime/ftplugin/snakemake.vim		@ribru17
 runtime/ftplugin/solidity.vim		@cothi
@@ -590,6 +591,7 @@ runtime/syntax/scss.vim			@tpope
 runtime/syntax/sdoc.vim			@gpanders
 runtime/syntax/sed.vim			@dkearns
 runtime/syntax/shared/debversions.vim	@jamessan
+runtime/syntax/shaderslang.vim          @mTvare6
 runtime/syntax/solidity.vim		@cothi
 runtime/syntax/spec.vim			@ignatenkobrain
 runtime/syntax/sqloracle.vim		@chrisbra

runtime/filetype.vim

@@ -2185,7 +2185,7 @@ au BufNewFile,BufRead [rR]antfile,*.rant,[rR]akefile,*.rake	setf ruby
 au BufNewFile,BufRead *.rs			setf rust
 au BufNewFile,BufRead Cargo.lock,*/.cargo/config,*/.cargo/credentials	setf toml
 
-" S-lang (or shader language, or SmallLisp)
+" S-lang
 au BufNewFile,BufRead *.sl			setf slang
 
 " Sage
@@ -2209,6 +2209,9 @@ au BufNewFile,BufRead *.scala			setf scala
 " SBT - Scala Build Tool
 au BufNewFile,BufRead *.sbt			setf sbt
 
+" Slang Shading Language
+au BufNewFile,BufRead *.slang			setf shaderslang
+
 " Slint
 au BufNewFile,BufRead *.slint			setf slint
 

runtime/ftplugin/shaderslang.vim

@@ -0,0 +1,54 @@
+" Vim filetype plugin file
+" Language:	Slang
+" Maintainer:	Austin Shijo <[email protected]>
+" Last Change:	2025 Jan 05
+
+" Only do this when not done yet for this buffer
+if exists("b:did_ftplugin")
+  finish
+endif
+
+" Don't load another plugin for this buffer
+let b:did_ftplugin = 1
+
+" Using line continuation here.
+let s:cpo_save = &cpo
+set cpo-=C
+
+let b:undo_ftplugin = "setl fo< com< cms< inc<"
+
+" Set 'formatoptions' to break comment lines but not other lines,
+" and insert the comment leader when hitting <CR> or using "o".
+setlocal fo-=t fo+=croql
+
+" Set comment string (Slang uses C-style comments)
+setlocal commentstring=//\ %s
+
+" Set 'comments' to format dashed lists in comments
+setlocal comments=sO:*\ -,mO:*\ \ ,exO:*/,s1:/*,mb:*,ex:*/,:///,://
+
+" When the matchit plugin is loaded, this makes the % command skip parens and
+" braces in comments properly, and adds support for shader-specific keywords
+if exists("loaded_matchit")
+  " Add common shader control structures
+  let b:match_words = '{\|^\s*\<\(if\|for\|while\|switch\|struct\|class\)\>:}\|^\s*\<break\>,' ..
+        \ '^\s*#\s*if\(\|def\|ndef\)\>:^\s*#\s*elif\>:^\s*#\s*else\>:^\s*#\s*endif\>,' ..
+        \ '\[:\]'
+  let b:match_skip = 's:comment\|string\|character\|special'
+  let b:match_ignorecase = 0
+  let b:undo_ftplugin ..= " | unlet! b:match_skip b:match_words b:match_ignorecase"
+endif
+
+" Win32 and GTK can filter files in the browse dialog
+if (has("gui_win32") || has("gui_gtk")) && !exists("b:browsefilter")
+  let b:browsefilter = "Slang Source Files (*.slang)\t*.slang\n"
+  if has("win32")
+    let b:browsefilter ..= "All Files (*.*)\t*\n"
+  else
+    let b:browsefilter ..= "All Files (*)\t*\n"
+  endif
+  let b:undo_ftplugin ..= " | unlet! b:browsefilter"
+endif
+
+let &cpo = s:cpo_save
+unlet s:cpo_save