Allow running arbitrary commands in lieu of choosing a compiler backend

[ashpil]

Is your feature request related to a problem? Please describe it.
I would like to use tectonic as my backend, but it does not natively support a continuous mode, so it would be nice if I could instruct vimtex to use a manual workaround.

Describe the solution you'd like
Using a wrapper like watchexec, one can have tectonic recompile a file every time it is changed, as described here: watchexec --exts tex tectonic file.tex.
If instead of explicitly instructing vimtex to use a given backend (vimtex_compiler_x) one could specify an arbitrary command to be run at the compile/livereload phase (vimtex_compiler_custom: tectonic [file] or vimtex_compiler_custom_live: watchexec --exts tex tectonic [file]), this would open vimtex up to a lot more customization at a very low cost, and allow users to use more backends without extra work for the maintainers.

Describe alternatives you've considered
I suppose you could just build some sort of watchexec feature into vimtex itself, but that doesn't seem nearly as appealing.

[lervag]

I've added a first version of a generic compiler. Can you test it and give some feedback? This is still very much WIP, but I hope it might be in the direction you want.

[SeniorMars]

Hello, I was trying to use this feature. Am I doing this correct? I tried passing flags to tectonic but I'm unsure how. I tried ``--`

let g:vimtex_compiler_method="generic"
let g:vimtex_compiler_generic = {
    \ 'cmd' : 'watchexec --exts tex tectonic',
    \ 'build_dir' : '',
    \}

[lervag]

Hello, I was trying to use this feature. Am I doing this correct?

Yes, this should work, I think. You don't need to specify the build dir if you don't actually specify it.

I don't use watchexec much, but I do use entr. I just tested this:

let g:vimtex_compiler_method = 'generic'
let g:vimtex_compiler_generic = {
    \ 'cmd' : 'ls *.tex|entr -c latexmk',
    \}

It works as expected. However, it should be noted that there are no callbacks (how would I implement a generic callback function anyhows?). But you can look at the output with \lo or :VimtexCompileOutput. This should also show you error messages if your command does not work.

By the way: why would you use the generic method when let g:vimtex_compiler_method = 'tectonic' already exists (see :help vimtex-tectonic)?

[BachoSeven]

@lervag As for your last question, I think that the original reason for OP to ask for a generic method was to enable combining tectonic with watchexec (or entr, I guess) to add "continuous" compilation functionality for tectonic, which does not support that yet.

[lervag]

@lervag As for your last question, I think that the original reason for OP to ask for a generic method was to enable combining tectonic with watchexec (or entr, I guess) to add "continuous" compilation functionality for tectonic, which does not support that yet.

Ah, that makes some sense, I guess. :) But, as I said, for me it seems to work as expected, so I would appreciate more details about what exactly is not working.

[BachoSeven]

I had not looked into it properly, now I tried again and it works, using entr to place the arguments in the right place for tectonic(not sure how to do the same argument substitution trick with watchexec):

	let g:vimtex_compiler_method='generic'
	let g:vimtex_compiler_generic = {
		\	'cmd': 'ls *.tex | entr -c tectonic /_ --synctex --keep-logs',
		\}

Since this is very useful as long as tectonic does not support continous compilation, so perhaps there could be another tectonic-continous backend which supports callback?
I understand this is a bit of a niche use, but since this is really what OP wanted from this "generic" compiler, perhaps it would be easier to make a wrapper around tectonic, using your favourite entr/watchexec program for detecting changes but with the same callback as the tectonic backend.

Sorry if the above doesn't make sense, I don't really know how the callback function works

[lervag]

I had not looked into it properly, now I tried again and it works,

Great, glad to hear it.

Since this is very useful as long as tectonic does not support continous compilation, so perhaps there could be another tectonic-continous backend which supports callback?

Nah, I don't like that. Instead, I think it could be possible to allow some custom callback functions. That is, I could implement the generic compilers output similar to how it is done with latexmk and allow hooks like what is possible for :help g:vimtex_compiler_latexmk (see the hooks key in the help text). That would allow something like this:

function! MyCustomCallback(msg) abort
  if condition(a:msg)
    call vimtex#compiler#callback(!vimtex#qf#inquire(b:vimtex.tex))
  endif
endfunction
let g:vimtex_compiler_generic = {
      \ 'cmd': 'ls *.tex | entr -c tectonic /_ --synctex --keep-logs',
      \ 'hooks': [function('MyCustomCallback')],
      \}

[lervag]

I've opened a new issue with a description of remaining tasks for the generic compiler. Feel free to comment. I'm closing this issue as it is preceded by the new issue.