lint: add "promise-function-async" rule

[tjconcept]

The rule promise-function-async seems like something I would want to enable.

[marvinhagemeister]

This rule requires type information which the current linter has no access to. We've recently landed support for JS plugins for our linter and aren't too far off from wiring up tsc into that. Once that's done it should be doable to run typescript-eslint rules with Deno's linter.

[tjconcept]

Aha. That sounds slow and expensive? Why wouldn't it get the type information from its own AST?

[marvinhagemeister]

To get type information you need to invoke tsc and look at more than the current file. The AST alone is not enough to get the type, except for very few obvious cases.

[tjconcept]

I see. I'm just curious.

Would this be possible to do in a performant way? I assume my IDE (Zed) is communicating with a long-running instance of the Deno LSP, but is it then rerunning the entire process of parsing the code, building an AST, passing to tsc, which builds its own AST, etc. on "every key stroke"?

[marvinhagemeister]

There is a bunch of code in place to avoid doing unnecessary work, although at some point you'll need to reparse the current file. I'm not too familiar with the LSP side of things, but I don't think it happens on every key stroke.