cape VS eglot

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!

Recently I stumbled upon this issue:

https://github.com/joaotavora/eglot/discussions/1127

I don't know enough about emacs and LSP to see the full picture, but it seems that both eglot's and corfu's maintainers, assumably very competent programmers, can't find a solution for this.

I only skimmed the thread. My understanding is that LSP dumps a long list of completion candidates at once and they can't decide a cache strategy that works well with existing code...?

It could be. There are unfixed issues with eglot and corfu, and sadly not a lot of willingness to investigate.

Eglot errors when I add new Python code blocks. The error disappears when I reconnect the language server, but the same happens again when I add a new code block. My "workaround" now is that before I start working on the .qmd file, I just add a bunch of Python code blocks (for which I also have a function) and then reconnect the language server again. This way I can start working for a while until I need to add more code blocks again.

This discussion has helped with some performance issues: https://github.com/joaotavora/eglot/discussions/993.

I guess eglot doesn't support it yet: https://github.com/joaotavora/eglot/pull/839

This is not by pure chance, João is the developer of the Eglot LSP client and the breadcrumbs from LSP-mode had been requested as a feature, but as far as I remember João thought rightfully that this could be an independent package, see https://github.com/joaotavora/eglot/discussions/988

A substantial section of the community is using corfu instead of company, but I wouldn't say company is out of date by any means. In emacs 29 eglot will be a built in, which might act as a replacement for lsp-mode depending on what functionality you need.

I am currently running emacs 29 (built from emacs-29 branch) which – according to https://github.com/joaotavora/eglot – should contain the latest eglot.

Yep. You can use flymake or flycheck for that in combination with eglot or lsp-mode.

See https://github.com/joaotavora/eglot#diagnostics

(I have reported this (that is, ElDoc missing docs for callable things at point, when Eglot is enabled) as an issue recently: First on GitHub-discussions https://github.com/joaotavora/eglot/discussions/1200, then on Debbugs https://debbugs.gnu.org/cgi/bugreport.cgi?bug=62687. But the threads are very long, so I don't recommend reading them.)