Typer regression in contextual higher kinded types

[WojciechMazur]

Compiler version

3.2.0-RC1-bin-20220429-400427d-NIGHTLY

Works with 3.1.2

First bad commit fe40c59 in #14840

Minimized code

Based on https://github.com/rssh/dotty-cps-async/blob/7563fc15c0de9efffee3d166d01f0e83d1d20433/shared/src/test/scala/cps/gopherlike/SLBase.scala#L136-L148

//> using scala "3.2.0-RC1-bin-20220429-400427d-NIGHTLY"
// //> using scala "3.1.2" // Last stable working version

case class Expr[+T](get: T)
trait Ctx[F[_]]
sealed trait Selector[F[_]]:
  def appended(base: Expr[SelectLoop[F]]): Expr[SelectLoop[F]]
  
 // Without Ctx[F] argument it would compile correctly
class SelectLoop[F[_]](using Ctx[F])
object SelectLoop:
  def loopImpl[F[_]](ctx: Ctx[F])(caseDefs: List[Selector[F]]): Expr[Unit] = 
    // Adding explicit type :Expr[SelectLoop[F]] satifies the compiler
    val s0 = Expr(new SelectLoop[F](using ctx)) 
    val g = caseDefs.foldRight(s0)(_.appended(_))
    Expr(())

Output

[error] ./test.scala:13:47: Found:    (_$6 : Expr[Object])
[error] Required: Expr[SelectLoop[F]]
[error] 
[error] where:    F is a type in method loopImpl with bounds <: [_] =>> Any
[error]     val g = caseDefs.foldRight(s0)(_.appended(_))
[error]                                               ^

Expectation

Should compile like in the 3.1.2, without need for explicit type annotation

[prolativ]

It looks like the problem occurs only if Ctx[F] is a using parameter of class SelectLoop and is passed to the constructor explicitly. So both

class SelectLoop[F[_]](ctx: Ctx[F])

...

    val s0 = Expr(new SelectLoop[F](ctx)) 

and

class SelectLoop[F[_]](using ctx: Ctx[F])

...

    given Ctx[F] = ctx
    val s0 = Expr(new SelectLoop[F]) 

work correctly.

[nicolasstucki]

Started failing in 3.2.0-RC1-bin-20220423-17ec9a7-NIGHTLY

[nicolasstucki]

First bad commit fe40c59 in #14840