Add CaseAccessor flag for case accessors

Was missing before.

Author: odersky

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

@@ -388,8 +388,9 @@ object desugar {
       val tparamAccessors = derivedTparams map { tdef =>
         cpy.TypeDef(tdef, originalTparams.next.mods, tdef.name, tdef.rhs, tdef.tparams)
       }
+      val caseAccessor = if (mods is Case) CaseAccessor else EmptyFlags
       val vparamAccessors = derivedVparamss.flatten map { vdef =>
-        cpy.ValDef(vdef, originalVparams.next.mods, vdef.name, vdef.tpt, vdef.rhs)
+        cpy.ValDef(vdef, originalVparams.next.mods | caseAccessor, vdef.name, vdef.tpt, vdef.rhs)
       }
       cpy.TypeDef(cdef, mods, name,
         cpy.Template(impl, constr, parents1, self1,

src/dotty/tools/dotc/core/Flags.scala

@@ -304,7 +304,7 @@ object Flags {
   /** Info can be refined during GADT pattern match */
   final val GADTFlexType = typeFlag(25, "<gadt-flex-type>")
 
-  /** A case parameter (or its accessor, or a GADT skolem) */
+  /** A case parameter accessor */
   final val CaseAccessor = termFlag(26, "<caseaccessor>")
 
   /** An type parameter which is an alias for some other (non-visible) type parameter */