Avoid using the pollster crate

[umbrageodotus]

Is your request related to a problem? Please describe.
As tokio is already being used in jj, pollster is somewhat unneeded and can cause deadlock-type issues.

Describe the solution you'd like
I'd like the uses of pollster to be replaced with using tokio::task::block_in_place, followed by Handle::current (or Handle::try_current on Result types where panicking would be unideal) for retrieving a handle to the tokio runtime, and finishing off with block_on to actually do the blocking. This boilerplate could be handled by a macro or another crate, I don't know.

Describe alternatives you've considered
Modifying anything that actually needs to run async code (for example, traits) to actually return a result and in implementations which don't need async, use std::future::ready.
Note: ideally, as to not wait for the complexity needed for this rewrite, this bandaid fix would be implemented immediately, followed by the future::ready idea asap.

Additional context
Testing would need to be modified. 2 obvious solutions:

1. Create a tokio runtime for the tests - would also make it more stable as traits provided by tokio are being used INSIDE of what is being tested
2. Allow for pollster by using Handle::try_current instead of Handle::current and falling back to pollster, although that seems like a bandaid fix

[benbrittain]

Currently tokio is an extremely minimal dependency of jj-lib. It's only purpose at the moment is to provide async trait interfaces, I would like to prefer avoiding propagating runtime expectations into jj-lib.

Most places that block_on is currently being used right now are places that I think are generally accepted that we'd like to have async interfaces in those spaces instead.

[umbrageodotus]

That was the second approach.

[umbrageodotus]

May I PR? Also, does jj-cli use tokio? It seems to only use pollster...

[martinvonz]

Yes, generally feel free to bubble up async-ness IMO. You may want to start with a small PR to make sure you're on the right track (according to what the rest of us are looking for).

[umbrageodotus]

Oh, wait, I can't. My system's fucked.

[benbrittain]

#7775

I put together a slew of changes that nearly remove pollster from jj-lib as a starting point