TypeVar tracing.

  % scala -Dscalac.debug.tvar

  scala> class Foo[CC[X] <: Traversable[X]] { def bar[T](xs: CC[T]) = xs.head }
  defined class Foo

  scala> new Foo bar List(1,2,3)
  [    create] ?CC                      ( In Foo[CC[X] <: Traversable[X]] )
  [    create] ?CC                      ( In Foo[CC[X] <: Traversable[X]] )
  [   setInst] Nothing                  ( In Foo[CC[X] <: Traversable[X]], CC=Nothing )
  [    create] ?CC                      ( In Foo[CC[X] <: Traversable[X]] )
  [    create] ?T                       ( In Foo[CC[X] <: Traversable[X]]#bar[T] )
  [    create] ?A                       ( In List#apply[A] )
  [    create] ?A                       ( In List#apply[A] )
  [   setInst] Int                      ( In List#apply[A], A=Int )
  [    create] ?CC                      ( In Foo[CC[X] <: Traversable[X]] )
  [    create] ?T                       ( In Foo[CC[X] <: Traversable[X]]#bar[T] )
  [    create] ?CC                      ( In Foo[CC[X] <: Traversable[X]] )
  [ applyArgs] ?CC                      ( In Foo[CC[X] <: Traversable[X]], apply args ?T to CC )
  [   setInst] List                     ( In Foo[CC[X] <: Traversable[X]], CC=List )
  [   setInst] Int                      ( In Foo[CC[X] <: Traversable[X]]#bar[T], T=Int )
  res0: Int = 1

Also, I gave TypeVar some polymorphism.  Review by @moors.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/files/neg/names-defaults-neg.check b/test/files/neg/names-defaults-neg.check
index 01ef54e0ea..01bbe2de4e 100644
--- a/test/files/neg/names-defaults-neg.check
+++ b/test/files/neg/names-defaults-neg.check
@@ -83,7 +83,7 @@ names-defaults-neg.scala:76: error: no type parameters for method test4: (x: T[T
  --- because ---
 argument expression's type is not compatible with formal parameter type;
  found   : List[Int]
- required: ?T[?T[List[?T[X forSome { type X }]]]]
+ required: ?T
 Error occurred in an application involving default arguments.
   test4()
   ^