Fix #1401: Make sure all refs are forwarded

Faced with recursive dependencies through self types, we might have
to apply `normalizeToClassRefs` to a class P with a parent that is not
yet initialized (witnessed by P's parents being Nil). In that case
we should still execute forwardRefs on P, but we have to
wait in a suspension until P is initialized.

This avoids the problem raised in #1401. I am still not quite sure
why forwardRefs is needed, but it seems that asSeenFrom alone is not
enough to track the dependencies in this case.

1 files changed, 25 insertions, 0 deletions

diff --git a/tests/pos/i1401.scala b/tests/pos/i1401.scala
new file mode 100644
index 000000000..140d78e7f
--- /dev/null
+++ b/tests/pos/i1401.scala
@@ -0,0 +1,25 @@
+package i1401
+
+trait Subtractable[A, +Repr <: Subtractable[A, Repr]] {
+  def -(elem: A): Repr
+}
+
+trait BufferLike[BA, +This <: BufferLike[BA, This] with Buffer[BA]]
+                extends Subtractable[BA, This]
+{ self : This =>
+
+  /* Without fix-#1401:
+   *
+     error: overriding method - in trait Subtractable of type (elem: A)This & i1401.Buffer[A];
+     method - of type (elem: BA)This has incompatible type
+     def -(elem: BA): This
+         ^
+     one error found
+  */
+  def -(elem: BA): This
+}
+
+trait Buffer[A] extends BufferLike[A, Buffer[A]]
+
+
+