3.0.0-RC2 Regression issue: type derivation of typed class not working well

[daenenk]

Compiler version

This issue popped up on scala "3.0.0-RC2" while I didn't saw it on 3.0.0-RC1

Minimized code

case class Box[A](a:A):
  def map[B](f: A => B): Box[B] = Box(f(a))

object T:
  box(1).map(_ + 1)

Output

[error] 41 |  box(1).map(_ + 1)
[error]    |             ^^^^^
[error]    |             Found:    Int => Int
[error]    |             Required: Boxed[Int]#A => Int

Expectation

Boxed[Int]#A should be recognized as being equivalent to Int in this case.

[daenenk]

PS: while moving from 3.0.0-RC1 to 3.0.0-RC2 I also switched to sbt 1.5.0 i.s.o. using the dotty-plugin as recommended on https://www.scala-lang.org/blog/2021/04/08/scala-3-in-sbt.html

[bishabosha]

Thank you for opening the issue, please may you update your example so it does not produce missing reference errors, for example box does not exist, and if i change it to Box then the code compiles

5 |  box(1).map(_ + 1)
  |  ^^^
  |  Not found: box

[daenenk]

Sorry, the minimized code is incomplete. And I had this on Scala 3.0.0-RC1 as well (I first though it was new). I posted the full issue already as a comment on #11729,
because I thought it may be strongly related.