Feature: Add support for Pyre for Python linting

[iheanyi]

With Facebook recently releasing Pyre, it would be good to have Pyre support for type checking within Syntastic.

[lcd047]

I looked at Pyre, and I'm not optimistic about being able to write a working syntastic checker for it.

First, it's isn't clear to me how this is supposed to be used. Monkeying the example in the demo, a small Python file with a type error produces an error message, but subsequently editing the file and moving the error around doesn't change the message from pyre (restarting the pyre server does though). The fact that editor integration is completely undocumented doesn't help.

Assuming this is addressed somehow, next roadblock is that pyre wants to be run from the project's root. Guessing project's root in Vim would be awkward at best.

Then there's the careless use of stderr. The other linter from Facebook, flow, used to have the same problem, and getting it fixed took more than an year (even though the fix itself was trivial). To this day the flow checker is still a trainwreck for many reasons, and it's one of the few checkers I regret adding to syntastic. I have very few reasons to believe a pyre checker would fare any better. shrug

[iheanyi]

I appreciate the detailed response @lcd047, all of your points are valid and I appreciate you taking the time to explain (especially given your previous experiences). Who knows, somebody else may make a PR adding support for pyre into Syntastic but after your explanation, I understand where the lack of optimism is coming from.