cache fold levels

[Konfekt]

To follow up on #2427 (comment) :

Yes, it will once, but then it just spits out the precomputed fold level for each line till the next change.
Whereas I am under the impression that as Vim implements &foldmethod=expr the function is called for every line and then each such has to redo the computation.
In contrast, this recomputation is only done once, how knows for which line (likely the first), and then stored and retrieved in all subsequent function calls (for higher line numbers).

This might be too apparent an idea, but somehow I never see this caching

[Konfekt]

I suppose the initial idea of &foldexpr was something like computing indent levels for each line individually, not the more intricate computations of syntax tree depths

[lervag]

Oh, yes, I think you are right. This is definitely something to consider! I'm a little behind on following up issues lately, so I'll likely not put this at top priority right now, but I'll get around to it unless you (or someone else) beats me to it. 😊

[Konfekt]

Thank you then for the kind consideration ;) This was just for inspiration rather than imposing deadlines; it might be as simple a change as adding the changedtick check around here

vimtex/autoload/vimtex/fold.vim

Line 114 in 44a2f12

let l:value = l:type.level(l:line, a:lnum)

[lervag]

Yes, I think you are right that this may be quite simple. :)

[lervag]

I've pushed a branch and opened a PR, see #3054. Let's continue the discussion there.