Implement lexigraphic ordering for PubKey

src/key.rs

@@ -64,7 +64,7 @@ pub const ONE_KEY: SecretKey = SecretKey([0, 0, 0, 0, 0, 0, 0, 0,
                                           0, 0, 0, 0, 0, 0, 0, 1]);
 
 /// A Secp256k1 public key, used for verification of signatures
-#[derive(Copy, Clone, PartialEq, Eq, Debug, PartialOrd, Ord, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
 pub struct PublicKey(ffi::PublicKey);
 
 impl fmt::LowerHex for PublicKey {
@@ -470,6 +470,18 @@ impl<'de> ::serde::Deserialize<'de> for PublicKey {
     }
 }
 
+impl PartialOrd for PublicKey {
+    fn partial_cmp(&self, other: &PublicKey) -> Option<::core::cmp::Ordering> {
+        self.serialize().partial_cmp(&other.serialize())
+    }
+}
+
+impl Ord for PublicKey {
+    fn cmp(&self, other: &PublicKey) -> ::core::cmp::Ordering {
+        self.serialize().cmp(&other.serialize())
+    }
+}
+
 #[cfg(test)]
 mod test {
     use Secp256k1;
@@ -512,6 +524,16 @@ mod test {
         assert!(compressed.is_ok());
     }
 
+    #[test]
+    fn pubkey_ordering() {
+        let pk1 = PublicKey::from_str("03cc0add20974ae5c73dcb1db8c157921403487943ecdc96f1f06bc5b189695590").unwrap();
+        let pk2 = PublicKey::from_str("0237869a55636998319161ae342085feeacc72397948b77a936c9c23c161645db6").unwrap();
+        let mut v = vec![pk1, pk2];
+        v.sort();
+        let expected = vec![pk2, pk1];
+        assert_eq!(v, expected);
+    }
+
     #[test]
     fn keypair_slice_round_trip() {
         let s = Secp256k1::new();