Address review comments

Author: mpilquist

library/src/scala/deriving/Mirror.scala

@@ -53,7 +53,7 @@ object Mirror {
   extension [T](p: ProductOf[T])
     /** Create a new instance of type `T` with elements taken from product `a`. */
     @annotation.experimental
-    def fromProductTyped[A <: scala.Product](a: A)(using m: ProductOf[A], ev: p.MirroredElemTypes =:= m.MirroredElemTypes): T =
+    def fromProductTyped[A <: scala.Product, Elems <: p.MirroredElemTypes](a: A)(using m: ProductOf[A] { type MirroredElemTypes = Elems }): T =
       p.fromProduct(a)
 
     /** Create a new instance of type `T` with elements taken from tuple `t`. */

tests/neg/deriving.scala

@@ -1,6 +1,6 @@
-import deriving.MirrorOf
+import reflect.Generic
 
-sealed trait A
+sealed trait A derives Generic // error: cannot take shape, it has anonymous or inaccessible subclasses
 
 object A {
   def f() = {
@@ -9,28 +9,17 @@ object A {
   }
 }
 
-def aMirror = summon[Mirror.Of[A]] // error: cannot take shape, it has anonymous or inaccessible subclasses
-
-sealed trait B
+sealed trait B derives Generic // error: cannot take shape, its subclass class D is not a case class
 
 class D(x: Int, y: String) extends B
 
-def bMirror = summon[Mirror.Of[B]] // error: cannot take shape, its subclass class D is not a case class
-
-class E
-def eMirror = summon[Mirror.Of[E]] // error: cannot take shape, it is neither sealed nor a case class
+class E derives Generic // error: cannot take shape, it is neither sealed nor a case class
 
-sealed trait F
-def fMirror = summon[Mirror.Of[F]] // error: cannot take shape, it has anonymous or inaccessible subclasses
+sealed trait F derives Generic // error: cannot take shape, it has anonymous or inaccessible subclasses
 
 object G {
   def f() = {
     case class H() extends F
   }
 }
 
-case class I(x: Int, y: String)
-object I:
-  def f = summon[deriving.Mirror.ProductOf[I]].fromProductTyped((1, 2)) // error
-  def g = summon[deriving.Mirror.ProductOf[I]].fromTuple((1, 2)) // error
-