Add a new bib parser written in Lua

[lervag]

Adding a lua parser for bibtex files.

See #2786.

[micangl]

I think there may be an issue. When testing this commit, I've noticed that the time it took for the context-menu to show up wasn't significantly lower. I've tried setting the g:vimtex_parser_bib_backend option to alternative with values, but to no avail: the time efficiency was always the same.

When debugging I've seen that, in practically all calls to the vimtex#parse#bib function, the argument { 'backend': 'vim'} is provided, effectively voiding the influence of the global backend option.

Also, in the lua/vimtex/bibparser.lua file, M.parse function, line 230, the format_entry is called on every entry; the goal of said function is to format the results in markdown and improve readability (which I don't think could be called a desired effect here?).

[lervag]

Yes, sorry, I didn't update the parser for the context menu yet - I've fixed this locally but not pushed it. Thanks for checking, though! Your too fast for me ;)

[lervag]

There, I think these are fixed now.

[lervag]

When debugging I've seen that, in practically all calls to the vimtex#parse#bib function, the argument { 'backend': 'vim'} is provided, effectively voiding the influence of the global backend option.

Yes; the reason for this is that the context menu needs the source file and line number entries that we do not get with the bibtex backend. The Vimscript parser was written mostly to support the context menu feature.

[micangl]

Ok, I've tested the new commit and everything seems to be working well.

[lervag]

I've improved the code now. It may not be much faster, but at least it is much easier to understand (IMHO).

[lervag]

I think that's about as far as I'll go with this. I'll leave the PR open a few days before merging in case anyone wants to test. But I think it should be fine and that it should provide a nice speedup for some people.

[lervag]

Ok, I've merged this now.

@micangl Notice that I've made some quite significant changes both to the Lua and the Vimscript parsers. I believe I've fixed some bugs in the process, and you should consider to either directly rely on the new VimTeX parser in cmp-vimtex or copy and adapt it as you see fit.