Fix erasure of Thistypes.

Thistypes erased to the underlying class. This is wrong. When seen as part of some other type,
a ThisType has to erase to the erasure of the underlying type (i.e. the erasure if the selftype
of the class). unittest-collections.scala failed with a MethodNotFound error because the erasure
was computed incorrectly.

On the other hand, a tree with a ThisType type, should keep the type, analogous to a
tree with a TermRef type.

1 files changed, 1 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/core/TypeErasure.scala b/src/dotty/tools/dotc/core/TypeErasure.scala
index abe5418d4..8abab9155 100644
--- a/src/dotty/tools/dotc/core/TypeErasure.scala
+++ b/src/dotty/tools/dotc/core/TypeErasure.scala
@@ -315,12 +315,8 @@ class TypeErasure(isJava: Boolean, semiEraseVCs: Boolean, isConstructor: Boolean
       val parent = tp.parent
       if (parent isRef defn.ArrayClass) eraseArray(tp)
       else this(parent)
-    case tp: TermRef =>
+    case _: TermRef | _: ThisType =>
       this(tp.widen)
-    case tp: ThisType =>
-      def thisTypeErasure(tpToErase: Type) =
-        erasureFn(isJava, semiEraseVCs = false, isConstructor, wildcardOK)(tpToErase)
-      thisTypeErasure(tp.cls.typeRef)
     case SuperType(thistpe, supertpe) =>
       SuperType(this(thistpe), this(supertpe))
     case ExprType(rt) =>