Don't copy function flags to the parameters

Author: natsukagami

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

@@ -1911,15 +1911,12 @@ object desugar {
   /** Make erased function definitions use only ValDefs */
   def makeErasedFunctionValDefs(tree: Function, pt: Type)(using Context): Function = {
     val Function(args, result) = tree
-    val flags = tree match
-      case tree: FunctionWithMods => tree.mods.flags
-      case _ => EmptyFlags
     args match {
       case (_ : ValDef) :: _ => tree // ValDef case can be easily handled
       case _ if !ctx.mode.is(Mode.Type) => tree
       case _ =>
         val applyVParams = args.zipWithIndex.map {
-          case (p, n) => makeSyntheticParameter(n + 1, p).withAddedFlags(flags)
+          case (p, n) => makeSyntheticParameter(n + 1, p)
         }
         tree match
           case tree: FunctionWithMods =>