Properly add erased flags for generated parameters in the parser

Author: natsukagami

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1587,11 +1587,14 @@ object Parsers {
         else infixType()
 
       in.token match
-        case ARROW | CTXARROW => functionRest(t :: Nil)
+        case ARROW | CTXARROW =>
+          erasedArgs.addOne(false)
+          functionRest(t :: Nil)
         case MATCH => matchType(t)
         case FORSOME => syntaxError(ExistentialTypesNoLongerSupported()); t
         case _ =>
           if isPureArrow then
+            erasedArgs.addOne(false)
             functionRest(t :: Nil)
           else
             if (erasedArgs.exists(_ == true) && !t.isInstanceOf[FunctionWithMods])