Add autocompletion support for custom languages

[mdboom]

We should have a hook so that languages other than Javascript can perform autocompletion.

[louisabraham]

I think it would be awesome to implement an interface for https://langserver.org/, at least for code completion and jump to def.

This is a standard to implement custom language features for editors.
It is currently supported by the major editors and languages.
Thus, one would just have to compile the language server to JS / WASM to have a full-featured editor in the browser.

And some langservers are already coded in javascript, like https://github.com/freebroccolo/ocaml-language-server

[bcolloran]

this is the first i've heard of langserver, and i think it sounds like a really interesting idea.

@louisabraham would you be interested in looking into this a bit as you explore ocaml integration? We'll put this on the roadmap, but we probably won't get to if for a bit, so if it's an itch you're excited to scratch we'd love to help you work through a PR! Thanks!

[mdboom]

I agree that using langserver as a base means we don't have to reinvent that API or any of the language backends -- just a little glue to handle the events in iodide. I agree it might be a while until we get to this, but it sounds like a good plan. Keep us posted on progress on this, @louisabraham, and I'll do the same when I find the time to do the Python autocompletion -- it would be great, as you suggest, to do all of that in a language-agnostic way.

[louisabraham]

Disclaimer: I discovered langservers a month ago. But I like it when I'm the first one to have the idea of connecting two cool open source projects.

I have to admit I am not an an expert of neither OCaml nor JS, but I'll definitely work on something usable for OCaml. If you wonder where my obsession with OCaml comes from, it is because I once dreamt of a usable OCaml-in-browser experiment, mostly to help fellow students getting started with OCaml.
The best would be a real toplevel compiled with js_of_ocaml, but an alternative would be to use BuckleScript. End of the OCaml off-topic :)

I don't think one should mix the difficulties and try to implement autocompletion for Python or OCaml first.

For Python it will probably require including a lot of dependencies, and the resulting experiment might not be very performant / responsive. A good idea would be to execute those with a faster python-in-browser interpreter like http://pypyjs.org/ or to transpile them with https://github.com/flexxui/pscript (currently the most performant transpiler IMHO).
So it might get very complicated, and become a big standalone project like the compilation of numpy&co for pyodide.

To begin, there is a cool Javascript-Typescript langserver that could be integrated by either plugging the JSON-RPC layer or, preferably, wiring the TypeScript interfaces.

Thanks to the standard, adding new langservers will be free if they are already written in JS/TS (like ocaml)
Else, if will require:

• compiling / transpiling the langserver (see above for the case of Python)
• wiring the API calls

[bcolloran]

related to #2141