fix defaultArgument body synthesis: assign type Any to all cases, so match tree does not try to find the lub

Author: EugeneFlesselle

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

@@ -562,9 +562,10 @@ class SyntheticMembers(thisPhase: DenotTransformer) {
       val getterDenot = companionTree.tpe.member(getterName)
       companionTree.select(TermRef(companionTree.tpe, getterName, getterDenot))
 
-    val withDefaultCases =
-      for (acc, idx) <- caseClass.caseAccessors.zipWithIndex if acc.is(HasDefault)
-      yield CaseDef(Literal(Constant(idx)), EmptyTree, defaultArgumentGetter(idx))
+    val withDefaultCases = for
+      (acc, idx) <- caseClass.caseAccessors.zipWithIndex if acc.is(HasDefault)
+      body = Typed(defaultArgumentGetter(idx), TypeTree(defn.AnyType)) // so match tree does try to find union of case types
+    yield CaseDef(Literal(Constant(idx)), EmptyTree, body)
 
     val withoutDefaultCase =
       val stringIndex = Apply(Select(index, nme.toString_), Nil)

tests/run/mirror-defaultArgument.scala

@@ -45,3 +45,8 @@ object Test extends App:
   val m5 = summon[Mirror.Of[outer.Inner]]
   assert(m5.defaultArgument(1) == 3 + 1)
   outer.localTest(9d)
+
+
+  // new defaultArgument match tree should be able to unify different default value types
+  case class Foo[T](x: Int = 0, y: String = "hi")
+