Cats Effect 1.0.0-RC

[alexandru]

Updates Monix to Cats-Effect 1.0.0-RC.

I managed to produce another gigantic PR, not sure how I do it 🙂 but many changes are superficial...

1. introduced Platform.composeErrors for those cases in which, given multiple exceptions, we need to combine and signal multiple errors somehow — the logic is platform independent, as on top of the JVM we're using Throwable#addSuppressed, but on top of JavaScript we're simply returning a CompositeException
2. modified StackFrame to no longer take an UncaughtExceptionHandler on error; this is a change to the internals of both Task and Coeval, as instead of reporting the error using a provided logger, we're now composing errors using Platform.composeErrors
3. implemented bracket and bracketCase for Coeval, Task and Iterant
4. Task now also implements the new Async#never; this posed difficulty in testing the new law, due to having to test for non-termination, which doesn't work well when we are testing Task#unsafeRunSync, so for those particular tests we're disabling the laws that test for non-termination
5. for Coeval I added parens to .runTry() and .run() to signal side effects, which is a generally agreed upon convention in Scala; this doesn't have an impact on binary or source compatibility, other than warnings; many of the files enumerated as changed are due to this
6. added redeem and redeemWith for Task and Coeval, as optimizations for attempt.map and attempt.flatMap respectively; see related issues: Add error-handling methods to EitherT typelevel/cats#2237 and Add IO#redeem and IO#redeemWith typelevel/cats-effect#191
7. in Iterant deprecated the old Iterant.bracket, replacing it with Iterant.resource
8. Iterant.resource relying on flatMap for use highlighted problems in Iterant#flatMap that were fixed
9. Iterant#bracket and Iterant.resource are now implemented in terms of a new doOnExitCase operator; and the now deprecated Iterant.bracket is implemented in terms of Iterant.resource and flatMap
10. Iterant.empty now returns the same reference, optimizing memory usage
11. Iterant#dump was made more useful by printing the type of the node at each step ... this happened due to me debugging Iterant.resource(acquire)(release).flatMap(use), which was pretty hard
12. the implementation for Iterant#doOnFinish is now gone, now being derived from doOnExitCase

So the new doOnExitCase for Iterant looks like this:

final def doOnExitCase(f: ExitCase[Throwable] => F[Unit])(implicit F: Sync[F]): Iterant[F, A] =
  IterantExitCallback.doOnExitCase(this, f) 

And then we can describe Iterant.resource:

  def resource[F[_], A](acquire: F[A])
    (release: A => F[Unit])
    (implicit F: Sync[F]): Iterant[F, A] = {

    suspendS(
      F.map(acquire) { a =>
        nextS[F, A](a, F.pure(Iterant.empty), F.unit)
          .doOnExitCase(_ => release(a))
      },
      F.unit)
  }

The deprecated Iterant.bracket:

  @deprecated("Use Iterant.resource", since="3.0.0-RC2")
  def bracket[F[_], A, B](acquire: F[A])
    (use: A => Iterant[F, B], release: A => F[Unit])
    (implicit F: Sync[F]): Iterant[F, B] =
    resource(acquire)(release).flatMap(use)

And the new Bracket implementation:

  final def bracketCase[B](use: A => Iterant[F, B])(release: (A, ExitCase[Throwable]) => Iterant[F, Unit])
    (implicit F: Sync[F]): Iterant[F, B] = {

    self.flatMap { a =>
      use(a).doOnExitCase(release(a, _).completeL)
    }
  }

Things left to do, but not addressed in this PR:

1. Observable#doOnExitCase
2. Observable.resource
3. Iterant#cancelable as a way to address cancelation in F[_], see Cancelation laws presuppose no interruption typelevel/cats-effect#192 (comment)
4. Task violates the Concurrent and ConcurrentEffect laws when it is executed with the auto-cancelable run loop active and that's a big problem
5. Task#bracket is broken in the presence of auto-cancelable run loops

[codecov]

Codecov Report

Merging #659 into master will decrease coverage by 0.16%.
The diff coverage is 84.68%.

@@            Coverage Diff             @@
##           master     #659      +/-   ##
==========================================
- Coverage   91.03%   90.87%   -0.17%     
==========================================
  Files         377      377              
  Lines       10032    10089      +57     
  Branches     1887     1900      +13     
==========================================
+ Hits         9133     9168      +35     
- Misses        899      921      +22