Dependent types + Match types type resolution issue

[0lejk4]

Compiler version

3.4.0-RC4

Minimized code

object Repro {
  trait Responsive {
    type Response
  }

  object Responsive {
    type Aux[R] = Responsive {type Response = R}
    type Response[R] = R match {case Aux[r] => r}
  }

  case class StringRequest(name: String) extends Responsive {
    type Response = String
  }

  def withImplicit[R <: Responsive](request: R)(implicit ct: scala.reflect.ClassTag[Responsive.Response[R]]): Responsive.Response[R] = ???

  def withFunction[R <: Responsive](request: R)(call: R => Responsive.Response[R]): Responsive.Response[R] = ???

  def stringWithFunction(req: StringRequest): String = withFunction(req)(_.getClass.getSimpleName)

  def stringWithImplicit(req: StringRequest): String = withImplicit(req)

  def main(args: Array[String]): Unit = {}
}

Output

[error] -- [E007] Type Mismatch Error: /Projects/Scala3/src/main/scala/Main.scala:105:73 
[error] 105 |  def stringWithFunction(req: StringRequest): String = withFunction(req)(_.getClass.getSimpleName)
[error]     |                                                                         ^^^^^^^^^^^^^^^^^^^^^^^^
[error]     |             Found:    Repro.StringRequest => String
[error]     |             Required: Repro.StringRequest =>
[error]     |               Repro.Responsive.Response[
[error]     |                 Repro.StringRequest]
[error]     |
[error]     | longer explanation available when compiling with `-explain`
[error] -- [E172] Type Error: /Projects/Scala3/src/main/scala/Main.scala:107:72 
[error] 107 |  def stringWithImplicit(req: StringRequest): String = withImplicit(req)
[error]     |                                                                        ^
[error]     |No ClassTag available for Repro.Responsive.Response[
[error]     |  Repro.StringRequest]
[error] two errors found
[error] (Compile / compileIncremental) Compilation failed

Expectation

Hello, decided to try out Scala 3.4.0-RC4 inside my project and found some strange behavior, this works on 3.3.1 and on 3.3.2-RC3.
If I explicitly fill the generic parameter error goes away.
Is this something that is already covered by existing issues or is this something new?

[soronpo]

Paging @sjrd

[Gedochao]

output from current main with -explain

-- [E007] Type Mismatch Error: repro.scala:19:73 -------------------------------
19 |  def stringWithFunction(req: StringRequest): String = withFunction(req)(_.getClass.getSimpleName)
   |                                                                         ^^^^^^^^^^^^^^^^^^^^^^^^
   |Found:    Repro.StringRequest => String
   |Required: Repro.StringRequest => Repro.Responsive.Response[Repro.StringRequest]
   |----------------------------------------------------------------------------
   | Explanation (enabled by `-explain`)
   |- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
   |
   | Tree: {
   |   def $anonfun(_$1: Repro.StringRequest):
   |     Repro.Responsive.Response[Repro.StringRequest] =
   |     _$1.getClass[Repro.StringRequest]().getSimpleName()
   |   closure($anonfun)
   | }
   | I tried to show that
   |   Repro.StringRequest => String
   | conforms to
   |   Repro.StringRequest => Repro.Responsive.Response[Repro.StringRequest]
   | but none of the attempts shown below succeeded:
   |
   |
   | The tests were made under a constraint with:
   |  uninstantiated variables:
   |  constrained types:
   |   [R <: Repro.Responsive]
   |     (request: R)
   |       (call: R => Repro.Responsive.Response[R]): Repro.Responsive.Response[R]
   |  bounds:
   |      R := Repro.StringRequest
   |  ordering:
   |  co-deps:
   |  contra-deps:
    ----------------------------------------------------------------------------
-- [E172] Type Error: repro.scala:21:72 ----------------------------------------
21 |  def stringWithImplicit(req: StringRequest): String = withImplicit(req)
   |                                                                        ^
   |No ClassTag available for Repro.Responsive.Response[Repro.StringRequest]
2 errors found

[sjrd]

Probably a missing .normalized around class tag synthesizing.

[WojciechMazur]

Bisect points to: 97725d7
Last good release: 3.4.0-RC1-bin-20231214-423cd6c-NIGHTLY
First bad release: 3.4.0-RC1-bin-20231218-ec2b8bc-NIGHTLY