Fixes to checkNonCyclic

Simplified logic and now check prefixes of TypeRefs.
Without the simplified logic we would get false cyclic errors for ski.scala.

Test case: flowops.scala

Fixes #1185.

1 files changed, 31 insertions, 0 deletions

diff --git a/tests/pos/flowops.scala b/tests/pos/flowops.scala
new file mode 100644
index 000000000..6aead26be
--- /dev/null
+++ b/tests/pos/flowops.scala
@@ -0,0 +1,31 @@
+object Test {
+  import language.higherKinds
+
+  class NotUsed
+
+  trait FO[+Out, +Mat] { self =>
+    type Repr[+O] <: FO[O, Mat] {
+      type Repr[+OO] = self.Repr[OO]
+    }
+    def map[T](f: Out => T): Repr[T] = ???
+  }
+
+  class Source[+O, +M] extends FO[O, M] {
+    type Repr[+OO] <: Source[OO, M]
+  }
+
+  class Flow[-I, +O, +M] extends FO[O, M] {
+    type Repr[+OO] <: Flow[I, OO, M]
+  }
+
+  implicit class x[O, M, F[o, m] <: FO[o, m]](val f: F[O, M]) extends AnyVal {
+    def xx(i: Int): f.Repr[O] = f.map(identity)
+  }
+
+  type IntFlow[O, M] = Flow[Int, O, M]
+
+  val s1 = new Source[Int, NotUsed].xx(12)
+  val s2: Source[Int, NotUsed] = s1
+  val f1 = x[Int, NotUsed, IntFlow](new Flow[Int, Int, NotUsed]).xx(12)
+  val f2: Flow[Int, Int, NotUsed] = f1
+}