Add runsAfterGroupOf constraint to ExtensionMethods

Author: odersky

src/dotty/tools/dotc/transform/ExtensionMethods.scala

@@ -30,6 +30,8 @@ class ExtensionMethods extends MiniPhaseTransform with DenotTransformer with Ful
   override def phaseName: String = "extmethods"
 
   override def runsAfter: Set[Class[_ <: Phase]] = Set(classOf[ElimRepeated])
+  
+  override def runsAfterGroupsOf = Set(classOf[FirstTransform]) // need companion objects to exist
 
   override def transform(ref: SingleDenotation)(implicit ctx: Context): SingleDenotation = ref match {
     case ref: ClassDenotation if ref is ModuleClass =>