Bringing the tree and icode checkers back to life.

  build/pack/bin/scalac -d /tmp -Ycheck-debug -Ycheck:all \
  src/compiler/scala/tools/nsc/Global.scala

That blows up in constructors as most files do, so also try it with
-Ycheck:icode to see the pretty icode output (for a little while anyway,
after which it will again blow up.)

Our work has only just begun! See test/checker-tests/fail*.scala for
11 examples of places where the checker cries foul. Many of them are
telling us about real issues and we should listen, but I will need help
to figure out which are legitimate and which should be eliminated by
altering the checkers.

This patch also hacks on some territory the checkers drew me into,
especially TypeKinds, where I figured anything which had been commented
out since 2005 was fair game.

(Optional) review by dragos. (The one place I know I could use a look is
in Checkers.scala, because I had to relax some checks and add at least
one newer opcode.)

1 files changed, 61 insertions, 0 deletions

diff --git a/test/checker-tests/fail6.scala b/test/checker-tests/fail6.scala
new file mode 100644
index 0000000000..c59be55c4e
--- /dev/null
+++ b/test/checker-tests/fail6.scala
@@ -0,0 +1,61 @@
+// BoxedUnit/Unit confusion involving while.
+//
+// Apply( // sym=method while$1, tpe=Unit, tpe.sym=class Unit, tpe.sym.owner=package scala
+//   Ident("while$1"), // sym=method while$1, sym.owner=method f, sym.tpe=()Unit, tpe=()Unit, tpe.sym=<none>,
+class Erasure {
+  def f(b: Boolean) = {
+    if (b) "abc"
+    else while (b) ()
+  }
+}
+
+// % work/check all -Xprint:erasure work/fail6.scala
+// TypeStack init: REFERENCE(type AnyRef)
+// [Not checkable: parser]
+// [Not checkable: namer]
+// [Not checkable: packageobjects]
+// [Now checking: typer]
+// [Now checking: superaccessors]
+// [Now checking: pickler]
+// [Now checking: refchecks]
+// [Now checking: selectiveanf]
+// [Now checking: liftcode]
+// [Now checking: selectivecps]
+// [Now checking: uncurry]
+// [Now checking: tailcalls]
+// [Not checkable: specialize]
+// [Not checkable: explicitouter]
+// [[syntax trees at end of erasure]]// Scala source: fail6.scala
+// package <empty> {
+//   class Erasure extends java.lang.Object with ScalaObject {
+//     def this(): Erasure = {
+//       Erasure.super.this();
+//       ()
+//     };
+//     def f(b: Boolean): java.lang.Object = if (b)
+//       "abc"
+//     else
+//       while$1(){
+//         if (b)
+//           {
+//             ();
+//             while$1()
+//           }
+//         else
+//           ();
+//         scala.runtime.BoxedUnit.UNIT
+//       }
+//   }
+// }
+//
+// [Now checking: erasure]
+// work/fail6.scala:4: error:
+// **** ERROR DURING INTERNAL CHECKING ****
+// type mismatch;
+//  found   : scala.runtime.BoxedUnit
+//  required: Unit
+//     else while (b) ()
+//          ^
+// one error found
+//
+//