Capturing a group in a pattern used in a Vim autocmd

Question

I need Vim to ignore the .tmpl file extension to enable syntax highlighting.

How can I rewrite this:

autocmd BufNewFile,BufRead *.lua.tmpl set filetype=lua

to be more general? I want to match the lua and use it in the filetype.

Something like this is what I want:

autocmd BufNewFile,BufRead *.\(.*\).tmpl set filetype=\1

I use Neovim and I am currently wrapping the above in vim.cmd(). If this is somehow easier to do with vim.api.nvim_create_autocmd, then this is fine, too.

One way would be to copy and paste for each file extension. Because I don't want to do that, I was going to make a chezmoi (dotfile manager) template that automatically finds all extensions that I need. I doubt that this will be good for performance, though. Also seems like a lot of work for something that sounds easy.

I tried to escape the pattern and somehow use \v magic but I am unable to. I wasn't able to find an example so I came here.

Answer 1

You could use something like

" ~/.vim/ftdetect/tmpl.vim
autocmd BufNewFile,BufRead *.tmpl execute 'set filetype='..matchlist(expand('<afile>'), '.*\.\(.*\)\.tmpl$')[1]

Better error handling would be worthwhile, however.

Answer 2

I would do:

for ext in ['lua', 'tex']
  execute 'autocmd BufNewFile,BufRead *.' .. ext .. '.tmpl set filetype=' .. ext
endormi

But bear in mind that, in general, the file extension (e.g. .py) could be different than the filetype (e.g. python)