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/libgraphviz/maybe_owned_vec.rs b/src/libgraphviz/maybe_owned_vec.rs
index 026db9d96f6..bd19f19cec6 100644
--- a/src/libgraphviz/maybe_owned_vec.rs
+++ b/src/libgraphviz/maybe_owned_vec.rs
@@ -73,8 +73,8 @@ impl<'a, T: PartialEq> PartialEq for MaybeOwnedVector<'a, T> {
 impl<'a, T: Eq> Eq for MaybeOwnedVector<'a, T> {}
 
 impl<'a, T: PartialOrd> PartialOrd for MaybeOwnedVector<'a, T> {
-    fn lt(&self, other: &MaybeOwnedVector<T>) -> bool {
-        self.as_slice().lt(&other.as_slice())
+    fn partial_cmp(&self, other: &MaybeOwnedVector<T>) -> Option<Ordering> {
+        self.as_slice().partial_cmp(&other.as_slice())
     }
 }