Make Given a modifier flag

This is in preparation for merging it with `Implied`. We already compensate for
it when printing modifiers by eliding it when it appear with `Param`.

Also, drop `hasFlag` again, since it is subsumed by the way we compute `_.mods`.

Author: odersky

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

@@ -462,7 +462,7 @@ object Flags {
 
   /** Flags representing source modifiers */
   private val CommonSourceModifierFlags: FlagSet =
-    commonFlags(Private, Protected, Final, Case, Implicit, Implied, Override, JavaStatic)
+    commonFlags(Private, Protected, Final, Case, Implicit, Implied, Given, Override, JavaStatic)
 
   final val TypeSourceModifierFlags: FlagSet =
     CommonSourceModifierFlags.toTypeFlags | Abstract | Sealed | Opaque

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

@@ -71,7 +71,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
 
   protected def PrintableFlags(isType: Boolean): FlagSet = {
     if (isType) TypeSourceModifierFlags | Module | Local
-    else TermSourceModifierFlags | Module | Local | Given
+    else TermSourceModifierFlags | Module | Local
   }.toCommonFlags
 
   override def nameString(name: Name): String =
@@ -707,7 +707,7 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       else (txt, vparamss)
     (txt /: paramss)((txt, params) =>
       txt ~
-      (Str(" given ") provided params.nonEmpty && hasFlag(params.head, Given)) ~
+      (Str(" given ") provided params.nonEmpty && params.head.mods.is(Given)) ~
       paramsText(params))
   }
   protected def valDefToText[T >: Untyped](tree: ValDef[T]): Text = {
@@ -810,9 +810,6 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
     Text(annotations.map(annotText), " ") ~~ flagsText ~~ (Str(kw) provided !suppressKw)
   }
 
-  private def hasFlag(tree: untpd.MemberDef, flag: FlagSet): Boolean =
-    tree.mods.is(flag) || tree.symbol.is(flag)
-
   def optText(name: Name)(encl: Text => Text): Text =
     if (name.isEmpty) "" else encl(toText(name))