VimtexEventCompileRunning event for continuous compilation

[Neelfrost]

Is your feature request related to a problem? Please describe it.
I would like to display the compile status on my statusline. Currently, vimtex provides 3 events that trigger when:

1. Compile is first started,
2. Compile is successful,
3. Compile has failed.

The above works great for single-shot compilation, but not when using continuous compilation, since compile runs every time the document is saved.

Describe the solution you'd like
I would like another event that is triggered when a cycle of continuous compilation runs.

[lervag]

This already exists, but I forgot to document it. You want the VimtexEventCompiling event. I've updated the docs now.

[lervag]

Note, if you want this for a statusline feature, then you don't need to rely on the events. I use a custom statusline, but I believe my code should be not so hard to read, see here:

https://github.com/lervag/dotnvim/blob/c07302353b0544c4c6923b06ef0281ebb5077c18/autoload/personal/statusline.vim#L148-L157

  let l:status = getbufvar(a:bufnr, 'vimtex').compiler.status + 1

  let [l:symbol, l:color] = get([
        \ ['[⏻] ', ''],
        \ ['[⏻] ', ''],
        \ ['[⟳] ', ''],
        \ ['[✔︎] ', 'SLInfo'],
        \ ['[✖] ', 'SLAlert']
        \], l:status)

The idea here is that the statusline can check the b:vimtex.compiler.status attribute, which is the current compiler status. The status values are the same as those documented at :help vimtex#compiler#callback, although the values -1 and 0 may appear. -1 indicates that the compiler was never started, and value 0 means it is not running.

[Neelfrost]

This is even better! Thank you! :)

[lervag]

No problem :)