enable additional compiler checks by default + fix [re-evaluate end of 2022]

[tomholub]

When trying to find fix for this issue I came across 2 useful flags for Swift concurrency - -Xfrontend -warn-concurrency -Xfrontend -enable-actor-data-race-checks (https://twitter.com/olebegemann/status/1421144304127463427)
These flags add additional code checks, which are not enabled by default, and they found 55 errors in our current code.

Originally posted by @sosnovsky in #1022 (comment)

After fixing, could we set these as errors instead of warnings? Also in CI.

[sosnovsky]

Xcode automatically shows differernt error types as error or warning, but current warnings will be errors in Swift 6 - Warnings in Swift 5.5 identify unsafe constructs, will become errors in Swift 6.

[tomholub]

Until then, could enable this:

[ivan-ushakov]

@tomholub
Can I start with this one or you have something with higher priority?

[tomholub]

You can start with this one. We don't have to treat warnings as errors yet, but should look into addressing as many warnings as possible.

You may want to do several smaller PRs so we don't run into merge conflicts.

Also: -Xfrontend -warn-concurrency -Xfrontend -enable-actor-data-race-checks - can this be enabled in the IDE for everyone? So that we all see the warnings.

[ivan-ushakov]

I found that enabling -Xfrontend -warn-concurrency produces a lot of warning about non sendable types. Not sure if we can fix them now because this requires a lot of changes in code.

I will try to fix errors produced by -Xfrontend -warn-concurrency.

[tomholub]

Not necessarily all at once. @sosnovsky are these sensible warnings to address?

[sosnovsky]

One of Swift language developers suggests not to use -warn-concurrency flag for now, as some warnings will be automatically fixed in the next Swift version (https://twitter.com/dgregor79/status/1470940523259056129).

So maybe for now we can fix only -enable-actor-data-race-checks warnings

[tomholub]

sounds good