Eliminate tpd.Modifiers.

Backend does not need them after all, can just use nulls there.
So the functionality is only used for printing, and it makes
sense to move everything there.

Author: odersky

src/dotty/tools/backend/jvm/DottyBackendInterface.scala

@@ -70,7 +70,7 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
   type Bind            = tpd.Bind
   type New             = tpd.New
   type Super           = tpd.Super
-  type Modifiers       = tpd.Modifiers
+  type Modifiers       = Null
   type Annotation      = Annotations.Annotation
   type ArrayValue      = tpd.JavaSeqLiteral
   type ApplyDynamic    = Null
@@ -944,7 +944,7 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
   }
 
   object ValDef extends ValDefDeconstructor {
-    def _1: Modifiers = tpd.Modifiers(field.symbol)
+    def _1: Modifiers = null
     def _2: Name = field.name
     def _3: Tree = field.tpt
     def _4: Tree = field.rhs
@@ -1055,7 +1055,7 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
   }
 
   object DefDef extends DefDefDeconstructor {
-    def _1: Modifiers = tpd.Modifiers(field.symbol)
+    def _1: Modifiers = null
     def _2: Name = field.name
     def _3: List[TypeDef] = field.tparams
     def _4: List[List[ValDef]] = field.vparamss
@@ -1081,7 +1081,7 @@ class DottyBackendInterface(outputDirectory: AbstractFile, val superCallsMap: Ma
   }
 
   object ClassDef extends ClassDefDeconstructor {
-    def _1: Modifiers = tpd.Modifiers(field.symbol)
+    def _1: Modifiers = null
     def _2: Name = field.name
     def _4: Template = field.rhs.asInstanceOf[Template]
     def _3: List[TypeDef] = Nil

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

@@ -19,11 +19,6 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
 
   private def ta(implicit ctx: Context) = ctx.typeAssigner
 
-  def Modifiers(sym: Symbol)(implicit ctx: Context): Modifiers = Modifiers(
-    sym.flags & (if (sym.isType) ModifierFlags | VarianceFlags else ModifierFlags),
-    if (sym.privateWithin.exists) sym.privateWithin.asType.name else tpnme.EMPTY,
-    sym.annotations map (_.tree))
-
   def Ident(tp: NamedType)(implicit ctx: Context): Ident =
     ta.assignType(untpd.Ident(tp.name), tp)
 

src/dotty/tools/dotc/printing/RefinedPrinter.scala

@@ -163,9 +163,14 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
     /** Print modifiers from symbols if tree has type, overriding the untpd behavior. */
     implicit def modsDeco(mdef: untpd.MemberDef)(implicit ctx: Context): untpd.ModsDecorator =
       new untpd.ModsDecorator {
-        def mods = if (mdef.hasType) tpd.Modifiers(mdef.symbol) else mdef.rawMods
+        def mods = if (mdef.hasType) Modifiers(mdef.symbol) else mdef.rawMods
       }
 
+    def Modifiers(sym: Symbol)(implicit ctx: Context): Modifiers = untpd.Modifiers(
+      sym.flags & (if (sym.isType) ModifierFlags | VarianceFlags else ModifierFlags),
+      if (sym.privateWithin.exists) sym.privateWithin.asType.name else tpnme.EMPTY,
+      sym.annotations map (_.tree))
+
     def isLocalThis(tree: Tree) = tree.typeOpt match {
       case tp: ThisType => tp.cls == ctx.owner.enclosingClass
       case _ => false