Use io-classes instead of unliftio

[jasagredo]

io-classes is a drop-in replacement for IO that allows to run code in IOSim which can simulate most aspects of IO (see).

[stevana]

If this is a drop-in replacement, then why is it a 1.6KLOC change?

[jasagredo]

Stylish-haskell accidentally replaced all LF with CRLF in a couple of long files. I will amend that probably tomorrow. You can see the diff excluding whitespace changes in GitHub in the meantime.

[jasagredo]

Much better now, without \rs 👍

[stevana]

Thanks, but I still don't understand why this change is needed. Can you give an example of what this allows you to do that you couldn't do before?

[jasagredo]

This allows us to run tests where the SUT runs in IOSim. We can now inject artificial file-system failures, exceptions, make time progress at different speed that real time, trace changes in TVars, or finding race conditions via IOSimPOR.

In IOG we are using this to run some tests and we use IOSim extensively, we vendored temporarily a version of Sequential.hs for this purpose.

[stevana]

Think you can provide an example that makes use of any of what you just mentioned? I don't see how finding races with IOSimPOR can work wth Sequentail.hs (nor Parallel.hs).

At the very least the changelog should be updated to mention these possibilities with links to docs.