Bad performance involving cats Resource and apply

[oyvindberg]

Compiler version

3.1.0, 3.1.1

Minimized code

I minimized it from production code, but didn't inline the needed parts from cats and cats effect.

import cats.effect.{IO, Resource}
import cats.implicits.catsSyntaxApply

val faster: Resource[IO, Int] = {
  val foo = Resource.liftK(IO(println(s"flaff")))
  foo *> Resource.pure(1)
}

val slower: Resource[IO, Int] =
  Resource.liftK(IO(println(s"flaff"))) *> Resource.pure(1)

Scastie doesn't show how long it takes to compile, but you can see the difference. Here is the link anyway https://scastie.scala-lang.org/nQC63vOCTG6GuodVwwWKOg

Output

The two expressions faster and slower are equivalent, but one has the definition broken up in two. note that no futher types are ascribed.
On my machine compiling slower takes about 10 seconds, while faster is nearly instant.

Expectation

[oyvindberg]

Asymptomatic wasn't the word I was looking for :D anyways, you get my point :)

[smarter]

Fixed literally yesterday: #14333 :) Try scalaVersion := "3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY".

[dwijnand]

Indeed. Before:

$ scala-cli clean i14366.fast.scala
$ time scala-cli compile -d org.typelevel::cats-effect:3.3.4 i14366.fast.scala
Compiling project (Scala 3.0.2, JVM)
Compiled project (Scala 3.0.2, JVM)
scala-cli compile -d org.typelevel::cats-effect:3.3.4 i14366.fast.scala  1.14s user 0.26s system 78% cpu 1.766 total

$ scala-cli clean i14366.slow.scala
$ time scala-cli compile -d org.typelevel::cats-effect:3.3.4 i14366.slow.scala
Compiling project (Scala 3.0.2, JVM)
Compiled project (Scala 3.0.2, JVM)
scala-cli compile -d org.typelevel::cats-effect:3.3.4 i14366.slow.scala  1.13s user 0.26s system 22% cpu 6.101 total

After:

$ scala-cli clean i14366.fast.scala
$ time scala-cli compile -S 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY -d org.typelevel::cats-effect:3.3.4 i14366.fast.scala
Compiling project (Scala 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY, JVM)
Compiled project (Scala 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY, JVM)
scala-cli compile -S 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY -d    1.09s user 0.26s system 78% cpu 1.717 total

$ scala-cli clean i14366.slow.scala
$ time scala-cli compile -S 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY -d org.typelevel::cats-effect:3.3.4 i14366.slow.scala
Compiling project (Scala 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY, JVM)
Compiled project (Scala 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY, JVM)
scala-cli compile -S 3.1.3-RC1-bin-20220126-8ae2962-NIGHTLY -d    1.09s user 0.24s system 72% cpu 1.833 total

[oyvindberg]

Awesome, thanks!