[Question] Combine default markdown syntax and vimtex syntax?

[Bekaboo]

Description

Some background:

1. I am aware that issues like vimtex#syntax#in_mathzone() not work correctly in markdown file. #2346 and other similar issues exist, but all of them seem to require installing vim-markdown. I want to do it without the plugin since I all I need is math concealing
2. I am using neovim with treesitter disabled for markdown and tex files

I want to combine the default markdown syntax and vimtex syntax, more specifically

1. use default markdown syntax in non-math zones
2. take advantage of vimtex's math cancellation in math zones

So I create ~/.config/nvim/syntax/markdown.vim like the following:

" Vim syntax file

if exists('b:current_syntax')
  finish
endif

" Include tex math in markdown
syn include @tex syntax/tex.vim
syn region mkdMath start="\\\@<!\$" end="\$" skip="\\\$" contains=@tex keepend
syn region mkdMath start="\\\@<!\$\$" end="\$\$" skip="\\\$" contains=@tex keepend

let b:current_syntax = 'markdown'

and it works great, now I have math cancellation in makrdown math zones:

However, as you see many other syntax elements, e.g. the header is not highlighted because I do not define them in the syntax file, so I source the nvim's default markdown syntax file in my custom syntax file:

if exists('b:current_syntax') || exists('b:_loaded_markdown_syntax')
  finish
endif

let b:_loaded_markdown_syntax = 1
runtime! syntax/markdown.vim

" Include tex math in markdown
syn include @tex syntax/tex.vim
syn region mkdMath start="\\\@<!\$" end="\$" skip="\\\$" contains=@tex keepend
syn region mkdMath start="\\\@<!\$\$" end="\$\$" skip="\\\$" contains=@tex keepend

let b:current_syntax = 'markdown'

Now I have syntax highlights from nvim's default syntax file, but the math zone isn't concealed anymore:

---

So I wonder where I did wrong and how I can have default markdown highlighting combined with vimtex's math conceal feature using a custom markdown syntax file? Thanks in advance!

Steps to reproduce

No response

Expected behavior

No response

Actual behavior

No response

Do you use a latexmkrc file?

No

VimtexInfo

Cannot use `:VimtexInfo` in markdown files.

[lervag]

I believe the problem is quite simple. You forgot to unlet b:current_syntax. This should work, I think:

if exists('b:current_syntax')
  finish
endif

runtime! syntax/markdown.vim
unlet b:current_syntax

" Include tex math in markdown
syn include @tex syntax/tex.vim
syn region mkdMath start="\\\@<!\$" end="\$" skip="\\\$" contains=@tex keepend
syn region mkdMath start="\\\@<!\$\$" end="\$\$" skip="\\\$" contains=@tex keepend

let b:current_syntax = 'markdown'

[Bekaboo]

@lervag That does not work, also the b:_loaded_markdown_syntax is needed to avoid the endless recursive of sourcing syntax/markdown.vim files, so this is the content in my current ~/.config/nvim/syntax/markdown.vim:

if exists('b:current_syntax') || exists('b:_loaded_markdown_syntax')
  finish
endif

let b:_loaded_markdown_syntax = 1
runtime! syntax/markdown.vim
unlet b:current_syntax

" Include tex math in markdown
syn include @tex syntax/tex.vim
syn region mkdMath start="\\\@<!\$" end="\$" skip="\\\$" contains=@tex keepend
syn region mkdMath start="\\\@<!\$\$" end="\$\$" skip="\\\$" contains=@tex keepend

let b:current_syntax = 'markdown'

and this is what I get -- all highlighting in markdown math zone disappears (e.g. it does not make a difference before/after adding unlet b:current_syntax). Can you repro? Thanks!

[Bekaboo]

I've also tried moving the syntax file to the after/syntax directory with only the following content to avoid sourcing nvim's default markdown syntax file manually:

syn include @tex syntax/tex.vim
syn region mkdMath start="\\\@<!\$" end="\$" skip="\\\$" contains=@tex keepend
syn region mkdMath start="\\\@<!\$\$" end="\$\$" skip="\\\$" contains=@tex keepend

but that does not give me math conceal in mathzones. Don't know why but the conceal works only if

1. the tex syntax is included in syntax/markdown.vim, not after/syntax/markdown.vim, and
2. the default markdown syntax file must not be sourced in syntax/markdown.vim

So it seems that the math concealing works only if nvim does not source the default markdown syntax file. I'm confused.