Make Scala2x a commonFlag and set to all symbols from from Scala 2

In particular fix Scala2x flag

Author: nicolasstucki

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

@@ -339,13 +339,6 @@ object Flags {
   /** A super accessor */
   final val Scala2SuperAccessor: FlagSet = termFlag(26, "<superaccessor>")
 
-  /** An unpickled Scala 2.x class */
-  final val Scala2x: FlagSet = typeFlag(26, "<scala-2.x>")
-
-  final val Scala2xTrait: FlagSet = Scala2x | Trait
-
-  final val SuperAccessorOrScala2x: FlagSet = Scala2x.toCommonFlags
-
   /** A method that has default params */
   final val DefaultParameterized: FlagSet = termFlag(27, "<defaultparam>")
 
@@ -394,6 +387,11 @@ object Flags {
   /** Symbol is an enum class or enum case (if used with case) */
   final val Enum: FlagSet = commonFlag(40, "<enum>")
 
+  /** An unpickled Scala 2.x symbol */
+  final val Scala2x: FlagSet = commonFlag(41, "<scala-2.x>")
+
+  final val Scala2xTrait: FlagSet = Scala2x | Trait
+
   /** Labeled with `erased` modifier (erased value)  */
   final val Erased: FlagSet = termFlag(42, "erased")
 
@@ -485,7 +483,7 @@ object Flags {
     Scala2ExistentialCommon | MutableOrOpaque | Touched | JavaStatic |
     CovariantOrOuter | ContravariantOrLabel | CaseAccessor.toCommonFlags |
     Extension.toCommonFlags | NonMember | Implicit | Implied | Permanent | Synthetic |
-    SuperAccessorOrScala2x | Inline
+    Scala2x | Inline
 
   /** Flags that are not (re)set when completing the denotation, or, if symbol is
    *  a top-level class or object, when completing the denotation once the class

compiler/src/dotty/tools/dotc/core/unpickleScala2/Scala2Unpickler.scala

@@ -472,9 +472,7 @@ class Scala2Unpickler(bytes: Array[Byte], classRoot: ClassDenotation, moduleClas
     }
 
     def finishSym(sym: Symbol): Symbol = {
-      if (sym.isClass) {
-        sym.setFlag(Scala2x)
-      }
+      sym.setFlag(Scala2x)
       if (!(isRefinementClass(sym) || isUnpickleRoot(sym) || (sym is Scala2Existential))) {
         val owner = sym.owner
         if (owner.isClass)

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -2655,7 +2655,7 @@ class Typer extends Namer
         tree.tpe <:< wildApprox(pt)
         readaptSimplified(Inliner.inlineCall(tree, pt))
       }
-      else if (tree.symbol.is(Macro, butNot = Inline)) {
+      else if (tree.symbol.is(Scala2Macro)) {
         if (ctx.settings.XignoreScala2Macros.value) {
           ctx.warning("Scala 2 macro cannot be used in Dotty. See http://dotty.epfl.ch/docs/reference/dropped-features/macros.html", tree.sourcePos)
           tree

tests/neg/override-scala2-macro.check

@@ -0,0 +1,3 @@
+<56..56> in override-scala2-macro.scala
+error overriding method f in class StringContext of type [A >: Any](args: Seq[A]): String;
+  method f of type [A >: Any](args: Seq[A]): String cannot be used here - only Scala-2 macros can override Scala-2 macros

tests/neg/override-scala2-macro.scala

@@ -0,0 +1,3 @@
+class Foo extends StringContext {
+  override inline def f[A >: Any](args: A*): String = ??? // error
+}