Drop rustc-serialize support

[dtolnay]

According to Rust release milestone predictions, rustc-serialize is scheduled to be deprecated in next month's beta release of Rust.

This would be a good time to let us know if there is any functionality you require from Serde before that happens.

[tomassedovic]

Thanks for the heads-up! I think we're good feature-wise, but there is something I'm not sure how to do properly:

This is a library, so I want to provide Serde to people that want it, but not force it on anyone. So the trait implementations are behind a feature flag.

I have to end up implementing the Serialize and Deserialize traits manually decause I can't put just the derive section behind cfg(serde). Is there a way to still use the codegen features but in a module separate from the struct definition?

[tomassedovic]

Hm, I've just realised I could duplicate the new struct inside the optional module, derive the serde traits on it and then just convert it to the original struct I actually want. This seems to work fine, so unless there's a more elegant way to do it, I'm happy with this.

#![cfg(feature = "serde")]

use super::Color as UpstreamColor;
use serde::ser::{Serialize, Serializer};
use serde::de::{Deserialize, Deserializer};

#[derive(Serialize, Deserialize)]
struct Color {
    r: u8,
    g: u8,
    b: u8,
}

impl Serialize for UpstreamColor {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error> where S: Serializer {
        let color = Color {r: self.r, g: self.g, b: self.b};
        color.serialize(serializer)
    }
}

impl Deserialize for UpstreamColor {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where D: Deserializer
    {
        let color = Color::deserialize(deserializer)?;
        Ok(UpstreamColor {r: color.r, g: color.g, b: color.b})
    }
}

[dtolnay]

#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
struct Color { /* ... */ }

[tomassedovic]

Wow, I completely forgot about cfg_attr. Thanks!