cape VS lsp-mode

Wow, interesting that my response is getting down voted. It seems not enough that I give away my work for free. Nevertheless I appreciate support from the community, as other Emacs package developers. The support is actually helpful. To clarify, publishing my configuration would translate into quite a bit of work, requiring separation of private and public bits.

At least for Elisp source block one can use font locking to create a custom Capf. Add cape-elisp-block from my Cape package to completion-at-point-functions. Even if you don't want to use Cape you could just copy it to your config. It is a short function.

You can use cape-history from my Cape package. This is similar to consult-history only utilizing completion-in-region instead of completing-read.

Haven't tried configuring it accordingly, but here's the docs: https://github.com/minad/cape

corfu is blazingly fast. Orderless is as well. What is not always blazingly fast is your completion providing backend. You didn't mention where your slow completions are coming from. An LSP server? Dabbrev? Maybe a remote machine? Have you combined results from various backends (e.g. using cape?). Some completions backends are unavoidably slow, others are just not well optimized.

The most straight forward solution is probably the package company-math. (that's what I use but with corfu and cape)

Some time I'll add a mixin for Cape which would make the completion stuff really nice.

If you're set on using the completion system (M-TAB) for this, you could install Cape and use the cape-abbrev command to complete your abbrevs.

Oh, of course your efforts are valuable. I didn't mean to sound discouraging in any way. The point made by /u/xenodium is good - if you have a special candidate source with special behavior, it makes sense to provide a separate lightweight Capf. In contrast, using Tempel for this purpose doesn't make much use of the actual template functionality. Tempel is only a good fit for Org blocks if you use it already anyway, as I do. There is also value in having reference Capfs around, which will be helpful when developers create their own new completion functions. This was also the intention when I created my Cape package, which comes with many simple Capfs. It is always interesting to see what other Emacs users come up with. I am thankful for such efforts - it is inspiring!

I also tried to the solutions suggested  and , but nothing worked. I moved the (setq lsp-keymap-...) line outside (and before) use-package. I also used :config (define-key lsp-load-map...) in my use-package block. But none of them worked.

Not sure how much this might help, but lsp-mode has lsp-yaml-select-buffer-schema and lsp-yaml-set-buffer-schema commands to pick schema from a list or set from a URI. Checking the source of them might give some hints about how the same could be implemented in eglot?

Beyond that you might as well embrace the suck and install autex with a language server: https://emacs-lsp.github.io/lsp-mode/

Smart completion these days is done primarily through LSP. eglot is fairly minimal but built-in as of 29, also available via GNU Elpa. lsp-mode is another option with more integrations and a bit more fleshed out.

lsp-mode: https://github.com/emacs-lsp/lsp-mode/issues/2080

Are you running emacs-29? It has numerous speed-ups compared to emacs-28 and older versions, many of them coded by Mattias Engdegård, e.g. commit def6fa4246. I have a fresh build of emacs-29 running on Linux and a new mac with an M1 CPU, and it's stupid fast. I don't use the native-comp feature. I rarely notice any hesitation or slowness. I don't use Elpy. I do use lsp mode.

Since you are doing code development, the first things to go for would be setting up your emacs packaging (installing use-package and melpa (use-package's documentation covers this) so you have more packages to choose from (do be careful to not just pick things willy nilly but research them a bit first)) and then setting up lsp-mode. lsp-mode lets you use LSP servers for the specific programming languages you work with in a somewhat unified fashion. You then need to install and setup the LSP servers for the languages you use, and possibly install language specific Emacs packages as support (note, Emacs has builtin functionality for many).

And first of all, I'm trying to understand, how is it connected to https://github.com/emacs-lsp/lsp-mode? I'm sure, that existed lsp implementations already parse source code. Why TreeSitter?