Turn global vars into vals

Some globally accessible vars were never updated; should be vals.

Author: odersky

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

@@ -136,7 +136,7 @@ object Flags {
   private final val FirstNotPickledFlag = 48
   private final val MaxFlag = 63
 
-  private var flagName = Array.fill(64, 2)("")
+  private val flagName = Array.fill(64, 2)("")
 
   private def isDefinedAsFlag(idx: Int) = flagName(idx) exists (_.nonEmpty)
 

src/dotty/tools/dotc/typer/Mode.scala

@@ -18,7 +18,7 @@ case class Mode(val bits: Int) extends AnyVal {
 object Mode {
   val None = Mode(0)
 
-  private var modeName = new Array[String](32)
+  private val modeName = new Array[String](32)
 
   def newMode(bit: Int, name: String): Mode = {
     modeName(bit) = name

test/dotty/partest/DPDirectCompiler.scala

@@ -13,7 +13,7 @@ class DPDirectCompiler(runner: DPTestRunner) extends nest.DirectCompiler(runner)
     val clogWriter = new PrintWriter(clogFWriter, true)
     clogWriter.println("\ncompiling " + sources.mkString(" ") + "\noptions: " + opts0.mkString(" "))
 
-    implicit var ctx: dotty.tools.dotc.core.Contexts.Context = {
+    implicit val ctx: dotty.tools.dotc.core.Contexts.Context = {
       val base = new dotty.tools.dotc.core.Contexts.ContextBase
       import base.settings._
       val ctx = base.initialCtx.fresh.setSetting(printtypes, true)