scala/scala — pull request #86 by odersky (2012-01-04 06:06:31+00:00)
Title: Fix for implicits problem SI 5354

The reason why the test case compiled without error is pretty devious: When checking the `Foo.x' implicit, a CyclicReference error occurs which causes the alternative to be discarded. Why a CylicReference? Because the inferencer tries to decide whether the owner of `z` is a subclass of the owner od `x`. To do this, it computed the info of the owner of `z1`, which is not complete because no result type for `f1` was given. Hence a CyclicReference error.

The fix is twofold: (1) We make isNonBottomSubClass smarter so that it always returns false if the symbol in question is not a type; hence the info need not be computed. (2) It's dubious to swallow CyclicReference errors anywhere, but I deemed it too risky to propagate them. But at least the CyclicReference is now logged if -Ylog-implicit is true. This hopefully spares future maintainers the same detective work I had to go through when digging this out.