Support 128bit integers

[KodrAus]

serde 1.0.62 1.0.60 was recently released with optional support for 128bit numbers. It would be good if we could wire them up to bincode. There's a convenient serde_if_integer128! macro that serde exposes we could use to automatically detect newer compilers, but that might not line up so well with byteorder's explicit i128 feature. Maybe we could do something like this:

In Cargo.toml:

[features]
i128 = ["byteorder/i128"]

In ser.rs or de.rs:

impl Serializer {
    serde_if_integer128! {
        #[cfg(feature = "i128")]
        fn serialize_i128(self, v: i128) -> Result<Self::Ok, Self::Error> {
            // use `byteorder` to serialize our value
        }

        #[cfg(not(feature = "i128"))]
        fn serialize_i128(self, v: i128) -> Result<Self::Ok, Self::Error> {
            let _ = v;
            Err(Error::custom("i128 is not supported. Enable the `i128` feature of `bincode`"))
        }

        ...
    }
}

so that vanilla bincode keeps working on older compilers, but has a more helpful error message if you accidentally use 128bit numbers without enabling the feature?

Or maybe we could work around it using some build.rs wizardry?

[KodrAus]

Hmm actually, if we wanted to do something with an explicit i128 feature on bincode maybe it would be better if it looked like:

impl Serializer {
    #[cfg(feature = "i128")]
    fn serialize_i128(self, v: i128) -> Result<Self::Ok, Self::Error> {
        // use `byteorder` to serialize our value
    }

    serde_if_integer128! {
        #[cfg(not(feature = "i128"))]
        fn serialize_i128(self, v: i128) -> Result<Self::Ok, Self::Error> {
            let _ = v;
            Err(Error::custom("i128 is not supported. Enable the `i128` feature of `bincode`"))
        }

        ...
    }
}

So that enabling it always tried to implement the method, but if it's available and not implemented then we suggest the feature.

[TyOverby]

This looks like a good plan!

Would you feel comfortable implementing it? If not, I can get to it later this week.

[KodrAus]

@TyOverby Sure! I'm happy to submit a PR for this.

[KodrAus]

Hi @TyOverby! Are you happy to push out a 1.0.1 patch with the 128bit number support?

[TyOverby]

Published!