SI-6895 Test cases to explain the limitations in tcpoly inference

I've determined that the failure in this bug report boils down
to SI-2712. Submitting my working as neg tests for posterity.

The type error disabmiguator develops a serious stutter with this
example. I'll fix that in the following commit.

1 files changed, 9 insertions, 0 deletions

diff --git a/test/files/neg/t6895b.check b/test/files/neg/t6895b.check
new file mode 100644
index 0000000000..3ebdb69309
--- /dev/null
+++ b/test/files/neg/t6895b.check
@@ -0,0 +1,9 @@
+t6895b.scala:20: error: could not find implicit value for parameter e: Foo[[X]Bar[[X]Or[String,X],X]]
+  implicitly[Foo[({type L[X] = Bar[StringOr, X]})#L]]
+            ^
+t6895b.scala:23: error: polymorphic expression cannot be instantiated to expected type;
+ found   : [F[_]]Foo[[X(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)]Bar[F,X(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)]]
+ required: Foo[[X(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)]Bar[[X]Or[String,X],X(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)(in type L)]]
+  barFoo(null) : Foo[({type L[X] = Bar[StringOr, X]})#L]
+        ^
+two errors found