Partially fix #1500: Implicit search breaks at a certain depth

The issue fixed here was introduced by 71027f15. The added `csyms.isEmpty` condition on `case nil =>` is always true, which is clearely a bug.

t1500c still fails with covariant (or contravariant) type parameters on `::`, but this seams to be a more complicated issue involving the typer.

1 files changed, 28 insertions, 0 deletions

diff --git a/tests/pos/t1500a.scala b/tests/pos/t1500a.scala
new file mode 100644
index 000000000..adf46329a
--- /dev/null
+++ b/tests/pos/t1500a.scala
@@ -0,0 +1,28 @@
+trait Step0
+trait Step1
+trait Step2
+trait Step3
+trait Step4
+trait Step5
+trait Step6
+
+object Steps {
+  implicit val Step0: Step0 = new Step0 {}
+  implicit def Step1(implicit p: Step0): Step1 = new Step1 {}
+  implicit def Step2(implicit p: Step1): Step2 = new Step2 {}
+  implicit def Step3(implicit p: Step2): Step3 = new Step3 {}
+  implicit def Step4(implicit p: Step3): Step4 = new Step4 {}
+  implicit def Step5(implicit p: Step4): Step5 = new Step5 {}
+  implicit def Step6(implicit p: Step5): Step6 = new Step6 {}
+}
+
+object StepsTest {
+  import Steps._
+
+  implicitly[Step0]
+  implicitly[Step1]
+  implicitly[Step2]
+  implicitly[Step3]
+  implicitly[Step4]
+  implicitly[Step6]
+}