Refine lub calculation.

When a reasonable lub cannot be arrived at by direct means, use the
bounds of the lub inputs to derive bounds for the lub rather than giving
up. Closes SI-4938, review by moors.

1 files changed, 4 insertions, 0 deletions

diff --git a/test/files/pos/t4938.scala b/test/files/pos/t4938.scala
new file mode 100644
index 0000000000..6e41312851
--- /dev/null
+++ b/test/files/pos/t4938.scala
@@ -0,0 +1,4 @@
+class A {
+  import scala.collection.mutable._
+  val xs = List(Set(), Seq())
+}