restore accidentally removed code

Author: liufengyun

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -409,6 +409,18 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
       Empty
   }
 
+  /* Erase a type binding according to erasure semantics in pattern matching */
+  def erase(tp: Type): Type = tp match {
+    case tp@AppliedType(tycon, args) => erase(tp.superType)
+      if (tycon.isRef(defn.ArrayClass)) tp.derivedAppliedType(tycon, args.map(erase))
+      else tp.derivedAppliedType(tycon, args.map(t => WildcardType(TypeBounds.empty)))
+    case OrType(tp1, tp2) =>
+      OrType(erase(tp1), erase(tp2))
+    case AndType(tp1, tp2) =>
+      AndType(erase(tp1), erase(tp2))
+    case _ => tp
+  }
+
   /** Space of the pattern: unapplySeq(a, b, c: _*)
    */
   def projectSeq(pats: List[Tree]): Space = {
@@ -555,7 +567,9 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
     // precondition: `tp1` should have the shape `path.Child`, thus `ThisType` is always covariant
     val thisTypeMap = new TypeMap {
       def apply(t: Type): Type = t match {
-        case t @ ThisType(tref) if !tref.symbol.isStaticOwner && !tref.symbol.is(Module)  =>
+        case tp @ ThisType(tref) if !tref.symbol.isStaticOwner && !tref.symbol.is(Module)  =>
+          // TODO: stackoverflow here
+          // newTypeVar(TypeBounds.upper(mapOver(tp.underlying)))
           newTypeVar(TypeBounds.upper(mapOver(tref & tref.classSymbol.asClass.givenSelfType)))
         case _ =>
           mapOver(t)