Fix erasure of trait info

After erasure, traits always extend object, and no other class.

The change flushed out three more problems, one in the handling of
Super trees in erasure, another in bridge method generation. and a
third that class RepeatedParam had Seq, which is a trait, as first parent.

1 files changed, 12 insertions, 7 deletions

diff --git a/src/dotty/tools/dotc/TypeErasure.scala b/src/dotty/tools/dotc/TypeErasure.scala
index 7920667e7..3f9149214 100644
--- a/src/dotty/tools/dotc/TypeErasure.scala
+++ b/src/dotty/tools/dotc/TypeErasure.scala
@@ -317,9 +317,19 @@ class TypeErasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wild
       if (cls is Package) tp
       else {
         def eraseTypeRef(p: TypeRef) = this(p).asInstanceOf[TypeRef]
-        val parents: List[TypeRef] =
+        val parents: List[TypeRef] = {
           if ((cls eq defn.ObjectClass) || cls.isPrimitiveValueClass) Nil
-          else removeLaterObjects(classParents.mapConserve(eraseTypeRef))
+          else {
+            def normalize(trs: List[TypeRef])(implicit ctx: Context): List[TypeRef] = trs match {
+              case tr :: trs1 =>
+                assert(!tr.classSymbol.is(Trait), cls)
+                val tr1 = if (cls is Trait) defn.ObjectClass.typeRef else tr
+                tr1 :: trs1.filterNot(_ isRef defn.ObjectClass)
+              case nil => nil
+            }
+            normalize(classParents.mapConserve(eraseTypeRef))
+          }
+        }
         val erasedDecls = decls.filteredScope(d => !d.isType || d.isClass)
         tp.derivedClassInfo(NoPrefix, parents, erasedDecls, erasedRef(tp.selfType))
           // can't replace selftype by NoType because this would lose the sourceModule link
@@ -376,11 +386,6 @@ class TypeErasure(isJava: Boolean, isSemi: Boolean, isConstructor: Boolean, wild
     cls
   }
 
-  private def removeLaterObjects(trs: List[TypeRef])(implicit ctx: Context): List[TypeRef] = trs match {
-    case tr :: trs1 => tr :: trs1.filterNot(_ isRef defn.ObjectClass)
-    case nil => nil
-  }
-
   /** The name of the type as it is used in `Signature`s.
    *  Need to ensure correspondence with erasure!
    */