vim-patch:5ddcecf: runtime(help): Add better support for language annotation highlighting

closes: vim/vim#16238

5ddcecf05f

Co-authored-by: Shougo Matsushita <Shougo.Matsu@gmail.com>
Co-authored-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: h_east <h.east.727@gmail.com>
(cherry picked from commit 60b866049c)

runtime/doc/helphelp.txt

@@ -373,17 +373,38 @@ To quote a block of ex-commands verbatim, place a greater than (>) character
 at the end of the line before the block and a less than (<) character as the
 first non-blank on a line following the block.  Any line starting in column 1
 also implicitly stops the block of ex-commands before it.  E.g. >
-    function Example_Func()
+	function Example_Func()
-	echo "Example"
+	  echo "Example"
-    endfunction
+	endfunction
 <
-It's possible to add Vim syntax highlighting support to code examples.  This
+
-can be done by adding "vim" after the greater than (>) character (">vim").
+To add annotation in the block, place the annotation (ex: "lua") after a
+greater than (>) character.  E.g: >lua
+	print("hello")
+<
+Note: uses lua syntax highlighting, if "lua" key is in
+|g:help_example_languages|.
+
+It's possible to add Vim syntax highlighting support to code examples.
 E.g: >vim
-    function Example_Func()
+	function Example_Func()
-	echo "Example"
+	  echo "Example"
-    endfunction
+	endfunction
 <
+						*g:help_example_languages*
+If you want to change the syntax highlighting in the block, you can
+change it like this: >
+	:let g:help_example_languages = #{ vim: 'vim', sh: 'bash' }
+The key represents the annotation marker name, and the value is the 'syntax'
+name.  By default, help files support only Vim script highlighting.
+Note: When setting "g:help_example_languages", if you do not include "vim"
+key, the Vim syntax highlighting will not be enabled. If you set it to an
+empty value, syntax highlighting for embedded languages will be disabled.
+
+Further note: including additional syntax languages into help files may not
+always work perfectly, if the included 'syntax' script does not account for
+such an import.
+						*help-notation*
 The following are highlighted differently in a Vim help file:
   - a special key name expressed either in <> notation as in <PageDown>, or
     as a Ctrl character as in CTRL-X

runtime/syntax/help.vim

@@ -12,28 +12,36 @@ endif
 let s:cpo_save = &cpo
 set cpo&vim
 
+if !exists('g:help_example_languages')
+  let g:help_example_languages = #{ vim: 'vim' }
+endif
+
 syn match helpHeadline		"^[A-Z.][-A-Z0-9 .,()_']*?\=\ze\(\s\+\*\|$\)"
 syn match helpSectionDelim	"^===.*===$"
 syn match helpSectionDelim	"^---.*--$"
 
-unlet! b:current_syntax
-" sil! to prevent E403
-silent! syntax include @VimScript syntax/vim.vim
-
-" Nvim: support language annotation in codeblocks
 if has("conceal")
-  syn region helpExample	matchgroup=helpIgnore start=" >[a-z0-9]*$" start="^>[a-z0-9]*$" end="^[^ \t]"me=e-1 end="^<" concealends
+  syn region helpExample	matchgroup=helpIgnore
-  syn region helpExampleVimScript matchgroup=helpIgnore
+        \ start="\%(^\| \)>[a-z0-9]*$" end="^[^ \t]"me=e-1 end="^<" concealends
-        \ start=/^>vim$/ start=/ >vim$/
-        \ end=/^[^ \t]/me=e-1 end=/^</ concealends
-        \ contains=@VimScript keepend
 else
-  syn region helpExample	matchgroup=helpIgnore start=" >[a-z0-9]*$" start="^>[a-z0-9]*$" end="^[^ \t]"me=e-1 end="^<"
+   syn region helpExample	matchgroup=helpIgnore
-  syn region helpExampleVimScript matchgroup=helpIgnore
+         \ start="\%(^\| \)>[a-z0-9]*$" end="^[^ \t]"me=e-1 end="^<"
-      \ start=/^>vim$/ start=/ >vim$/
-      \ end=/^[^ \t]/me=e-1 end=/^</
-      \ contains=@VimScript keepend
 endif
+
+for [s:lang, s:syntax] in g:help_example_languages->items()
+  unlet! b:current_syntax
+  " silent! to prevent E403
+  execute 'silent! syn include' $'@helpExampleHighlight_{s:lang}'
+        \ $'syntax/{s:syntax}.vim'
+
+  execute $'syn region helpExampleHighlight_{s:lang} matchgroup=helpIgnore'
+        \ $'start=/\%(^\| \)>{s:lang}$/'
+        \ 'end=/^[^ \t]/me=e-1 end=/^</'
+        \ (has("conceal") ? 'concealends' : '')
+        \ $'contains=@helpExampleHighlight_{s:lang} keepend'
+endfor
+unlet! s:lang s:syntax
+
 syn match helpHyperTextJump	"\\\@<!|[#-)!+-~]\+|" contains=helpBar
 syn match helpHyperTextEntry	"\*[#-)!+-~]\+\*\s"he=e-1 contains=helpStar
 syn match helpHyperTextEntry	"\*[#-)!+-~]\+\*$" contains=helpStar