Made "mode" into a value class.

This is an obvious place to apply value class goodness and
collect some safety/sanity in typing modes. It does show off
a challenge in introducing value classes without disruption:
there's no way to deprecate the old signature of 'typed',
'adapt', etc. because they erase the same.

  class Bippy(val x: Int) extends AnyVal
  class A {
    @deprecated("Use a bippy") def f(x: Int): Int = 5
    def f(x: Bippy): Int = x.x
  }

  ./a.scala:5: error: double definition:
  method f:(x: Bippy)Int and
  method f:(x: Int)Int at line 4
  have same type after erasure: (x: Int)Int

An Int => Mode implicit handles most uses, but nothing can
be done to avoid breaking anything which e.g. extends Typer
and overrides typed.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/files/pos/CustomGlobal.scala b/test/files/pos/CustomGlobal.scala
index 30bf227950..a5668bd7c0 100644
--- a/test/files/pos/CustomGlobal.scala
+++ b/test/files/pos/CustomGlobal.scala
@@ -22,7 +22,7 @@ class CustomGlobal(currentSettings: Settings, reporter: Reporter) extends Global
     override def newTyper(context: Context): Typer = new CustomTyper(context)
 
     class CustomTyper(context : Context) extends Typer(context) {
-      override def typed(tree: Tree, mode: Int, pt: Type): Tree = {
+      override def typed(tree: Tree, mode: Mode, pt: Type): Tree = {
         if (tree.summaryString contains "Bippy")
           println("I'm typing a Bippy! It's a " + tree.shortClass + ".")