Implement RFC#28: Add PartialOrd::partial_cmp

[sfackler]

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

[sfackler]

Test compilation failures:

rustc: x86_64-unknown-linux-gnu/stage2/test/coretest-x86_64-unknown-linux-gnu
/home/sfackler/rust/rust/src/libcore/iter.rs:2222:21: 2222:37 error: mismatched types: expected `core::option::Option<core::cmp::Ordering>` but found `option::Option<<generic #426>>` (expected enum core::option::Option but found enum option::Option)
/home/sfackler/rust/rust/src/libcore/iter.rs:2222                     Some(cmp::Equal) => (),
                                                                      ^~~~~~~~~~~~~~~~
/home/sfackler/rust/rust/src/libcore/iter.rs:2223:38: 2223:44 error: mismatched types: expected `option::Option<core::cmp::Ordering>` but found `core::option::Option<core::cmp::Ordering>` (expected enum option::Option but found enum core::option::Option)
/home/sfackler/rust/rust/src/libcore/iter.rs:2223                     non_eq => return non_eq,
                                                                                       ^~~~~~
/home/sfackler/rust/rust/src/libcore/iter.rs:3036:13: 3038:14 error: method `partial_cmp` has an incompatible type for trait: expected enum core::option::Option but found enum option::Option
/home/sfackler/rust/rust/src/libcore/iter.rs:3036             fn partial_cmp(&self, _: &Foo) -> Option<Ordering> {
/home/sfackler/rust/rust/src/libcore/iter.rs:3037                 None
/home/sfackler/rust/rust/src/libcore/iter.rs:3038             }
/home/sfackler/rust/rust/src/libcore/option.rs:151:30: 151:40 error: mismatched types: expected `core::option::Option<core::cmp::Ordering>` but found `option::Option<core::cmp::Ordering>` (expected enum core::option::Option but found enum option::Option)
/home/sfackler/rust/rust/src/libcore/option.rs:151 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/option.rs:151:1: 152:4 note: expansion site
/home/sfackler/rust/rust/src/libcore/option.rs:151:30: 151:40 error: if and else have incompatible types: expected `option::Option<core::cmp::Ordering>` but found `core::option::Option<core::cmp::Ordering>` (expected enum core::option::Option but found enum option::Option)
/home/sfackler/rust/rust/src/libcore/option.rs:151 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/option.rs:151:1: 152:4 note: expansion site
/home/sfackler/rust/rust/src/libcore/option.rs:151:30: 151:40 error: method `partial_cmp` has an incompatible type for trait: expected enum core::option::Option but found enum option::Option
/home/sfackler/rust/rust/src/libcore/option.rs:151 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/option.rs:151:1: 152:4 note: expansion site
/home/sfackler/rust/rust/src/libcore/result.rs:286:30: 286:40 error: mismatched types: expected `core::option::Option<core::cmp::Ordering>` but found `option::Option<core::cmp::Ordering>` (expected enum core::option::Option but found enum option::Option)
/home/sfackler/rust/rust/src/libcore/result.rs:286 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/result.rs:286:1: 287:2 note: expansion site
/home/sfackler/rust/rust/src/libcore/result.rs:286:30: 286:40 error: if and else have incompatible types: expected `option::Option<core::cmp::Ordering>` but found `core::option::Option<core::cmp::Ordering>` (expected enum core::option::Option but found enum option::Option)
/home/sfackler/rust/rust/src/libcore/result.rs:286 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/result.rs:286:1: 287:2 note: expansion site
/home/sfackler/rust/rust/src/libcore/result.rs:286:30: 286:40 error: mismatched types: expected `core::option::Option<core::cmp::Ordering>` but found `option::Option<core::cmp::Ordering>` (expected enum core::option::Option but found enum option::Option)
/home/sfackler/rust/rust/src/libcore/result.rs:286 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/result.rs:286:1: 287:2 note: expansion site
/home/sfackler/rust/rust/src/libcore/result.rs:286:30: 286:40 error: if and else have incompatible types: expected `option::Option<core::cmp::Ordering>` but found `core::option::Option<core::cmp::Ordering>` (expected enum core::option::Option but found enum option::Option)
/home/sfackler/rust/rust/src/libcore/result.rs:286 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/result.rs:286:1: 287:2 note: expansion site
/home/sfackler/rust/rust/src/libcore/result.rs:286:30: 286:40 error: method `partial_cmp` has an incompatible type for trait: expected enum core::option::Option but found enum option::Option
/home/sfackler/rust/rust/src/libcore/result.rs:286 #[deriving(Clone, PartialEq, PartialOrd, Eq, Ord, Show)]
                                                                                ^~~~~~~~~~
note: in expansion of #[deriving]
/home/sfackler/rust/rust/src/libcore/result.rs:286:1: 287:2 note: expansion site
error: aborting due to 11 previous errors
/home/sfackler/rust/rust/mk/tests.mk:384: recipe for target 'x86_64-unknown-linux-gnu/stage2/test/coretest-x86_64-unknown-linux-gnu' failed
make: *** [x86_64-unknown-linux-gnu/stage2/test/coretest-x86_64-unknown-linux-gnu] Error 101

[thestinger]

JSON objects are unordered key-value maps, and I don't really like that we've extended it with ordering semantics based on key comparisons. I've only ever seen JSON objects mapped to hash tables, not ordered maps (except in C++98, where there was no standard hash table). I wouldn't worry much about trying to get that ordering right, because I don't think it's a good idea to be doing it in the first place.

[alexcrichton]

r=me when coretest is passing, thanks!

[sfackler]

It seems like the right way forward here is to extract libcore's tests to a separate crate. I'm working on that now, and this can go in on top of that.

[huonw]

Hm, why does this need staging?

[sfackler]

The snapshot's deriving won't generate partial_cmp so there needs to be a default impl.

[huonw]

Ah, tricky!

[sfackler]

@huonw updated