Merge pull request #11610 from dotty-staging/fix-#11563

Add regression test

Author: nicolasstucki

tests/run/i11563.scala

@@ -0,0 +1,29 @@
+import scala.compiletime.{constValue, erasedValue, summonInline}
+import scala.deriving.Mirror
+
+trait Printer[T]:
+  def format: String
+
+given Printer[String] with
+  def format: String = "String"
+
+inline given[T](using mirror: Mirror.ProductOf[T]): Printer[T] = Printer.derived[T]
+
+object Printer:
+  inline def apply[T](using printer: Printer[T]): Printer[T] = printer
+
+  inline def derived[T](using mirror: Mirror.ProductOf[T]): Printer[T] =
+    val params = summonPrinters[mirror.MirroredElemTypes]
+    new Printer[T] :
+      def format: String = params.map(p => p.format).mkString(",")
+
+inline def summonPrinters[Types <: Tuple]: Seq[Printer[?]] = inline erasedValue[Types] match
+  case _: EmptyTuple => Seq.empty
+  case _: (v *: vs) => summonInline[Printer[v]] +: summonPrinters[vs]
+
+case class Simple(name: String)
+
+object Test:
+  def main(args: Array[String]): Unit =
+    assert(Printer[String].format == "String")
+    assert(Printer[Simple].format == "String")