JSON serialization of HashMaps with Enum keys is broken

[japaric]

STR

extern crate serialize;

use serialize::json;
use std::collections::HashMap;

#[derive(Encodable, Eq, Hash, PartialEq)]
enum Enum {
    Foo,
    Bar,
}

fn main() {
    let mut map = HashMap::new();
    map.insert(0, 0);
    println!("{}", json::encode(&map));

    let mut map = HashMap::new();
    map.insert(Enum::Foo, 0);
    println!("{}", json::encode(&map));
    println!("^ what?!");
}

Output

{"0":0}
{
^ what?!

Version

rustc 1.0.0-nightly (29bd9a06e 2015-01-20 23:03:09 +0000)

The second hashmap was properly being serialized as {"Foo":0} with a two days old nightly (rustc 1.0.0-nightly (dcaeb6aa2 2015-01-18 11:28:53 +0000)).

cc @aturon @alexcrichton @gankro

[alexcrichton]

cc @oli-obk

[bluss]

I think it is that json::encode ignores encoder errors and the error case is new -- not a valid map key.

[bluss]

Related PR #19490 Since encoding errors there now, the obvious bug would be that the error is suppressed silently.