add test to check override of defaultArgument (when and only when needed)

Author: EugeneFlesselle

tests/run/mirror-defaultArgument/MirrorOps.scala

@@ -0,0 +1,25 @@
+import scala.deriving._
+import scala.annotation.experimental
+import scala.quoted._
+
+object MirrorOps:
+
+  inline def overridesDefaultArgument[T]: Boolean = ${ overridesDefaultArgumentImpl[T] }
+
+  def overridesDefaultArgumentImpl[T](using Quotes, Type[T]): Expr[Boolean] =
+    import quotes.reflect.*
+    val cls = TypeRepr.of[T].classSymbol.get
+    val companion = cls.companionModule.moduleClass
+    val methods = companion.declaredMethods
+
+    val experAnnotType = Symbol.requiredClass("scala.annotation.experimental").typeRef
+
+    Expr {
+      methods.exists { m =>
+        m.name == "defaultArgument" &&
+        m.flags.is(Flags.Synthetic) &&
+        m.annotations.exists(_.tpe <:< experAnnotType)
+      }
+    }
+
+end MirrorOps

tests/run/mirror-defaultArgument/test.scala

@@ -0,0 +1,23 @@
+import scala.deriving._
+import scala.annotation.experimental
+import scala.quoted._
+
+import MirrorOps.*
+
+object Test extends App:
+
+  case class WithoutDefault(x: Int)
+  assert(!overridesDefaultArgument[WithoutDefault])
+
+
+  case class WithDefault(x: Int, y: Int = 1)
+  assert(overridesDefaultArgument[WithDefault])
+
+  val m = summon[Mirror.Of[WithDefault]]
+  assert(m.defaultArgument(1) == 1)
+
+  try
+    m.defaultArgument(0)
+    throw IllegalStateException("There should be no default argument")
+  catch
+    case ex: NoSuchElementException => assert(ex.getMessage == "0") // Ok