Deriving Serialize for a struct from external crate which uses generics

[AntoineBalaine]

Hello,
I'm trying to implement Serialize for nom_locate's LocatedSpan. It's a struct that encapsulates a token with some location information. can't figure out how to implement Serialize for it.

I created a WrappedSpan to build the bridge with LocatedSpan, but the derive macro doesn't chew up the passed-in generic. Is there a way around this?

#[derive(Serialize, Deserialize)]
#[serde(remote = "LocatedSpan<T>")] // <= This <T> produces an un-parseable token
struct WrappedSpan<T: AsBytes>{
    #[serde(getter = "LocatedSpan::location_offset")]
    offset: usize,
    #[serde(getter = "LocatedSpan::location_line")]
    line: u32,
    #[serde(getter = "LocatedSpan::fragment")]
    fragment: T,
};

// Provide a conversion to construct the remote type.
impl <T: AsBytes>From<WrappedSpan<T>> for LocatedSpan<T> {
    fn from(def: WrappedSpan<T>) -> LocatedSpan<T> {
        LocatedSpan{
            offset: def.offset,
            line: def.line,
            fragment: def.fragment,
            extra: (),
        }
    }
}

[AntoineBalaine]

Thank you for this update!

[dtolnay]

Fixed in serde_derive 1.0.148. You need to use serde(remote = "LocatedSpan").

[AntoineBalaine]

Could you be a bit more specific ? I can't seem to figure it out with the update:

#[derive(Serialize, Deserialize, PartialEq, Eq)]
#[serde(remote = "LocatedSpan")]
struct WrappedSpan<T: AsBytes> {
    #[serde(getter = "LocatedSpan::location_offset")]
    offset: usize,
    #[serde(getter = "LocatedSpan::location_line")]
    line: u32,
    #[serde(getter = "LocatedSpan::fragment")]
    fragment: T,
}

impl<T: AsBytes> From<WrappedSpan<T>> for LocatedSpan<T> {
    fn from(def: WrappedSpan<T>) -> LocatedSpan<T> {
        LocatedSpan::new(def.fragment)
    }
}

#[test]
fn serialize_located_span() {
    let input = LocatedSpan::new("");
    let serialized = serde_json::to_string(&input).unwrap(); //<= the trait bound `LocatedSpan<&str>: Serialize` is not satisfied
    let converted = "{\"offset\":0,\"line\":1,\"fragment\":\"\",\"column\":1}";
    assert_eq!(serialized, converted)
}