Fix #4470: compiler crash for repeated Enums

Author: Sebastian Nadorp

compiler/src/dotty/tools/dotc/ast/DesugarEnums.scala

@@ -210,7 +210,8 @@ object DesugarEnums {
 
   /** Expand a simple enum case */
   def expandSimpleEnumCase(name: TermName, mods: Modifiers, pos: Position)(implicit ctx: Context): Tree =
-    if (enumClass.typeParams.nonEmpty) {
+    if(!enumClass.exists) EmptyTree
+    else if (enumClass.typeParams.nonEmpty) {
       val parent = interpolatedEnumParent(pos)
       val impl = Template(emptyConstructor, parent :: Nil, EmptyValDef, Nil)
       expandEnumModule(name, impl, mods, pos)

tests/neg/enum-repeated-4470.scala

@@ -0,0 +1,10 @@
+object RepeatedEnum {
+
+  enum Maybe { //error
+    case Foo
+  }
+
+  enum Maybe { //error
+    case Foo
+  }
+}