Implement RFC#28: Add PartialOrd::partial_cmp

I ended up altering the semantics of Json's PartialOrd implementation.
It used to be the case that Null < Null, but I can't think of any reason
for an ordering other than the default one so I just switched it over to
using the derived implementation.

This also fixes broken `PartialOrd` implementations for `Vec` and
`TreeMap`.

RFC: 0028-partial-cmp

1 files changed, 2 insertions, 2 deletions

diff --git a/src/libcoretest/iter.rs b/src/libcoretest/iter.rs
index bc55b17b346..86b5ffece41 100644
--- a/src/libcoretest/iter.rs
+++ b/src/libcoretest/iter.rs
@@ -707,8 +707,8 @@ fn test_range() {
     }
 
     impl PartialOrd for Foo {
-        fn lt(&self, _: &Foo) -> bool {
-            false
+        fn partial_cmp(&self, _: &Foo) -> Option<Ordering> {
+            None
         }
     }