Do not add mirrors under -Yscala2-stdlib

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/SyntheticMembers.scala

@@ -639,8 +639,9 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
     val clazz = ctx.owner.asClass
     val syntheticMembers = serializableObjectMethod(clazz) ::: serializableEnumValueMethod(clazz) ::: caseAndValueMethods(clazz)
     checkInlining(syntheticMembers)
-    addMirrorSupport(
-      cpy.Template(impl)(body = syntheticMembers ::: impl.body))
+    val impl1 = cpy.Template(impl)(body = syntheticMembers ::: impl.body)
+    if ctx.settings.Yscala2Stdlib.value then impl1
+    else addMirrorSupport(impl1)
   }
 
   private def checkInlining(syntheticMembers: List[Tree])(using Context): Unit =

project/MiMaFilters.scala

@@ -185,10 +185,6 @@ object MiMaFilters {
         // Companion module class: Missing type java.io.Serializable
         ProblemFilters.exclude[MissingTypesProblem]("scala.*$"),
 
-        // Mirrors
-        ProblemFilters.exclude[DirectMissingMethodProblem]("scala.*.ordinal"),
-        ProblemFilters.exclude[DirectMissingMethodProblem]("scala.*.fromProduct"),
-
         // Case class product accessors
         ProblemFilters.exclude[DirectMissingMethodProblem]("scala.*._1"),
         ProblemFilters.exclude[DirectMissingMethodProblem]("scala.*._2"),

stdlib-bootstrapped/test/Main.scala

@@ -1,6 +1,7 @@
 package hello
 
-import scala.util.Right
+import scala.util.*
+import scala.compiletime.testing.typeChecks
 
 enum Color:
   case Red, Green, Blue
@@ -13,6 +14,7 @@ object HelloWorld:
     println(Color.Blue)
 
     testScala2UnapplySignatures()
+    testScala2ObjectParents()
   }
 
   def testScala2UnapplySignatures() = {
@@ -24,3 +26,8 @@ object HelloWorld:
     val _: Option[(Int, Int)] = Tuple2.unapply((1, 2))
     val _: Option[(Int, Int, Int)] = Tuple3.unapply((1, 2, 3))
   }
+
+  def testScala2ObjectParents() = {
+    assert(!typeChecks("Either: scala.deriving.Mirror.Sum"))
+    assert(!typeChecks("Either: scala.deriving.Mirror"))
+  }