Regression in apache/pekko-connectors for derivation

[WojciechMazur]

Based on OpenCB failure for apache/pekko-connectors - build logs

Compiler version

Since 3.4.0
Last good release: 3.4.0-RC1-bin-20231212-97e4401-NIGHTLY
First bad release: 3.4.0-RC1-bin-20231213-9dce045-NIGHTLY
Bisect points to d6c7e18

Minimized code

import scala.deriving.Mirror

type FieldType[K, +V] = (K, V)
type ZipWith[T1 <: Tuple, T2 <: Tuple, F[_, _]] <: Tuple = (T1, T2) match
  case (h1 *: t1, h2 *: t2) => F[h1, h2] *: ZipWith[t1, t2, F]
  case (EmptyTuple, ?)      => EmptyTuple
  case (?, EmptyTuple)      => EmptyTuple
  case _                    => Tuple

trait LabelledGeneric[A]:
  type Repr <: Tuple

object LabelledGeneric:
  type Aux[A, R] = LabelledGeneric[A] { type Repr = R }
  inline given productInst[A <: Product](using m: Mirror.ProductOf[A]): LabelledGeneric.Aux[A, ZipWith[m.MirroredElemLabels, m.MirroredElemTypes, FieldType]] =
    new LabelledGeneric[A]:
      type Repr = ZipWith[m.MirroredElemLabels, m.MirroredElemTypes, FieldType]

trait PdxEncoder[A]
object PdxEncoder:
  given objectEncoder[A, Repr <: Tuple](using LabelledGeneric.Aux[A, Repr]): PdxEncoder[A] = ???

case class Person(id: Int, name: String)

@main def Test =
  val fails: PdxEncoder[Person] = PdxEncoder.objectEncoder // error

Output

-- [E172] Type Error: /Users/wmazur/projects/scala3/bisect/test.scala:27:58 ----
27 |  val fails: PdxEncoder[Person] = PdxEncoder.objectEncoder
   |                                                          ^
   |No given instance of type LabelledGeneric.Aux[Person, Repr] was found for parameter x$1 of given instance objectEncoder in object PdxEncoder.
   |I found:
   |
   |    LabelledGeneric.productInst[Person](
   |      Person.$asInstanceOf[
   |        
   |          scala.deriving.Mirror.Product{
   |            type MirroredMonoType = Person; type MirroredType = Person;
   |              type MirroredLabel = ("Person" : String);
   |              type MirroredElemTypes = (Int, String);
   |              type MirroredElemLabels = (("id" : String), ("name" : String))
   |          }
   |        
   |      ]
   |    )
   |
   |But given instance productInst in object LabelledGeneric does not match type LabelledGeneric.Aux[Person, Repr]
   |
   |where:    Repr is a type variable with constraint <: Tuple
   |.

Expectation

Should probably compile

Workaround

Defining LabelledGeneric.productInst as transparent inline fixes the problem

[WojciechMazur]

Closing as it works as expected, the commit mentioned in bisect describes that it's expected