Print given clauses.

These were printed as old-style implicit parameters before.

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`.

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

@@ -705,7 +705,10 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
     val (leading, paramss) =
       if (isExtension && vparamss.nonEmpty) (paramsText(vparamss.head) ~ " " ~ txt, vparamss.tail)
       else (txt, vparamss)
-    (txt /: paramss)((txt, params) => txt ~ paramsText(params))
+    (txt /: paramss)((txt, params) =>
+      txt ~
+      (Str(" given ") provided params.nonEmpty && params.head.mods.is(Given)) ~
+      paramsText(params))
   }
   protected def valDefToText[T >: Untyped](tree: ValDef[T]): Text = {
     import untpd.{modsDeco => _}
@@ -797,7 +800,9 @@ class RefinedPrinter(_ctx: Context) extends PlainPrinter(_ctx) {
       else if (suppressKw) PrintableFlags(isType) &~ Private
       else PrintableFlags(isType)
     if (homogenizedView && mods.flags.isTypeFlags) flagMask &~= ImplicitOrImplied // drop implicit/implied from classes
-    val flags = (if (sym.exists) sym.flags else (mods.flags)) & flagMask
+    val rawFlags = if (sym.exists) sym.flags else mods.flags
+    if (rawFlags.is(Param)) flagMask = flagMask &~ Given
+    val flags = rawFlags & flagMask
     val flagsText = if (flags.isEmpty) "" else keywordStr(flags.toString)
     val annotations =
       if (sym.exists) sym.annotations.filterNot(ann => dropAnnotForModText(ann.symbol)).map(_.tree)