auto merge of #15030 : sfackler/rust/partial-cmp, r=huonw

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`.

# Note
This isn't ready to merge yet since libcore tests are broken as you end up with 2 versions of `Option`. The rest should be reviewable though.

RFC: 0028-partial-cmp

1 files changed, 5 insertions, 0 deletions

diff --git a/src/libstd/gc.rs b/src/libstd/gc.rs
index 44988a23070..80f1cbe6cb2 100644
--- a/src/libstd/gc.rs
+++ b/src/libstd/gc.rs
@@ -24,6 +24,7 @@ use default::Default;
 use fmt;
 use hash;
 use kinds::marker;
+use option::Option;
 use ops::Deref;
 use raw;
 
@@ -59,6 +60,10 @@ impl<T: PartialEq + 'static> PartialEq for Gc<T> {
 }
 impl<T: PartialOrd + 'static> PartialOrd for Gc<T> {
     #[inline]
+    fn partial_cmp(&self, other: &Gc<T>) -> Option<Ordering> {
+        (**self).partial_cmp(&**other)
+    }
+    #[inline]
     fn lt(&self, other: &Gc<T>) -> bool { *(*self) < *(*other) }
     #[inline]
     fn le(&self, other: &Gc<T>) -> bool { *(*self) <= *(*other) }