inline macro summoning valueOf[`h` & T] works if first using summonFrom with valueOf[`h`]

[eejbyfeldt]

Compiler version

Tested on Scala 3.7.3 and 3.8.0-RC1-bin-20251023-9ec1f84-NIGHTLY.

Minimized code

The code below contains two version that summon as singletons in a Tuple

//> using scala 3.7.3

import scala.compiletime.{erasedValue, summonFrom}

object test {
  // This version fails with "cannot reduce summonFrom"
  private inline def singletons[T, Elem <: Tuple]: Seq[T] =
    inline erasedValue[Elem] match {
      case _: EmptyTuple => Seq.empty
      case _: (h *: t) => valueOf[`h` & T] +: singletons[T, t]
    }

  // This version works when wrapped in summonFrom
  private inline def singletons2[T, Elem <: Tuple]: Seq[T] =
    inline erasedValue[Elem] match {
      case _: EmptyTuple => Seq.empty
      case _: (h *: t) =>
        summonFrom {
          case _: ValueOf[`h`] => valueOf[`h` & T] +: singletons2[T, t]
        }
    }

  enum A { case A1, A2, A3 }

  def main(args: Array[String]): Unit =
    println(singletons[A, (A.A1.type, A.A2.type, A.A3.type)]) // Fails
    println(singletons2[A, (A.A1.type, A.A2.type, A.A3.type)]) // Works: List(A1, A2, A3)
}

Output

Compiling project (Scala 3.7.3, JVM (21))
[error] ./bug_test.scala:22:13
[error] cannot reduce summonFrom with
[error]  patterns :  case given ev @ _:ValueOf[(test.A.A1 : test.A) & test.A]
[error]     println(singletons[A, (A.A1.type, A.A2.type, A.A3.type)]) // cannot reduce summonFrom
[error]             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Error compiling project (Scala 3.7.3, JVM (21))
Compilation failed

When the line with singletons is commented out and singletons2 is used instead:

Compiling project (Scala 3.7.3, JVM (21))
Compiled project (Scala 3.7.3, JVM (21))
List(A1, A2, A3)

Expectation

The behavior feels inconsistent. Either both should work or neither.