SI-7872 Plug a variance exploit in refinement types

Refinement types are collapsed to a TypeTree with an original
during type checking; this was enough to evade variance validation
in refchecks.

This commit:

  - validates the original of `TypeTree`s in refchecks
  - changes VarianceValidator to recurse into:
    - the originals of `TypeTree`s
    - `TypTree` (to cover, e.g. `CompoundTypeTree` / `SelectFromTypeTree`)

It also finds an unreported variance violation in an existing
test case, variances.scala. This looks to be legitimate.

1 files changed, 4 insertions, 1 deletions

diff --git a/test/files/neg/variances.check b/test/files/neg/variances.check
index 7d965e94dc..cb1a60a632 100644
--- a/test/files/neg/variances.check
+++ b/test/files/neg/variances.check
@@ -1,6 +1,9 @@
 variances.scala:4: error: covariant type A occurs in contravariant position in type test.Vector[A] of value x
   def append(x: Vector[A]): Vector[A]
              ^
+variances.scala:75: error: covariant type A occurs in contravariant position in type => A => A of value m
+      val m: A => A
+          ^
 variances.scala:18: error: covariant type A occurs in contravariant position in type A of value a
     private def setA3(a : A) = this.a = a
                       ^
@@ -19,4 +22,4 @@ variances.scala:89: error: covariant type T occurs in invariant position in type
 variances.scala:90: error: covariant type T occurs in contravariant position in type => test.TestAlias.B[C.this.A] of method foo
     def foo: B[A]
         ^
-7 errors found
+8 errors found