Ligatures and concealment

[filipmartinovic]

Hello, I've tried to add \dj and \DJ to list of ligatures in my local vimtex plugin to include this Croatian letter. I modified vimtex/autoload/vimtex/syntax/core.vim at lines 171 and 172 in following way:

  syntax match texCmdLigature "\v\\%([ijolL]|ae|dj|oe|ss|AA|AE|DJ|OE)$"
  syntax match texCmdLigature "\v\\%([ijolL]|ae|dj|oe|ss|AA|AE|DJ|OE)\ze[^a-zA-Z@]"

This does seem to work in recognizing \dj and \DJ as ligatures.

However, I also added following two lines below line 2480:

  syntax match texCmdLigature "\\DJ\>" conceal cchar=Đ
  syntax match texCmdLigature "\\dj\>" conceal cchar=đ

I find that neither \dj nor \DJ are concealed to characters đ and Đ, respectively.

Do you know what else should be done to achieve this concealment or did I do something wrong?

Also, would you consider adding these ligatures to the main repository? Thank you!

[filipmartinovic]

Well, I just realized that I did something wrong. I forgot to turn on concealment for ligatures

vim.g.vimtex_syntax_conceal = {
  accents = 1,
  ligatures = 1,
}

However I am still interested if you'd consider adding these ligatures to the main respository.

If yes, would you consider also concealing trailing space character after command? Letter đ never appears at the end of the word in Croatian

[filipmartinovic]

Thank you very much!

I looked at the change, it looks great, but I think this might cause problems in some cases. For instance in German one might have a sentence "VimTeX macht spaß für alle", which I'd write in my .tex file as VimTeX macht spa\ss f\" ur alle.. But now with this new change this would be concealed as VimTeX macht spaßfür alle. which would be incorrect. I guess that most words do not end with ligatures as last character, but these cases can cause unwanted behaviour as in this example.

I'm not sure what is the best solution here.

In Croatian this is not a problem as neither \dj nor \DJ are the last letter of a word. But now that I think about it, I don't know if some other language has same ligature and also a word with this ligature as the last letter.

If we were to conceal the following space character it seems that we would have to somehow know if it is the end of the word or not.

Or actually maybe this is not necessary. One idea that comes to mind is to make it so that it conceals at most one space character. In this way, using ligature as normal would conceal that one space character after it. However, for one to write sentence "VimTeX macht spaß für alle" in .tex, in this case they could write VimTeX macht spa\ss f\" ur alle. (notice double space character), which would in this case render as VimTeX macht spaß für alle. as it would conceal only one space character after \ss and leave the other space character in place.

What do you think about this?

[lervag]

which I'd write in my .tex file as VimTeX macht spa\ss f\" ur alle..

Well, this is how it looks on my end (the compiled PDF in white behind and above, and neovim with (left) and without (right) conceals):

Notice that, without the extra \ , the compiled version of VimTeX macht spa\ss f\" ur alle. is not what you expect.

[lervag]

The point, and the reason why the current version is correct (I'm pretty sure), is that any tex command \foo will alway swallow every following space.

[filipmartinovic]

Aha yes you are right, I see what you mean, on your image it looks all good! Well that is great, then I also believe that the current version is correct!

(I notice that on my machine the \ doesn't conceal to the space character (it just remains as is), but I currently have access only to my work machine where I still have locked VimTeX to v2.15, so I assume this is only on my end.)

[lervag]

Let me know if it looks wrong when you update to main (I do recommend not locking to tags unless for specific reasons).