Support for the bounds serde attribute.

[abizjak]

It is sometimes necessary to have either phantom types or special bounds for types for the structs. serde supports supplying custom bounds on these types so that the derived instance has useful bounds, instead of requiring all type parameters to have the Serialize/Deserialize bounds.

It does not appear that schemars honors these.

Concretely, I would like this to work

#[derive(Serialize, Deserialize)]
#[derive(JsonSchema)] 
#[serde(bound = "A: Sized")]
struct S<A> {
    x: u64,
    #[serde(skip)]
    a: PhantomData<A>
}

struct Dummy;

fn f() {
    let schema = schema_for!(S<Dummy>);
}

[GREsau]

This is already supported via the #[schemars(bound = "...")] attribute - see https://graham.cool/schemars/deriving/attributes/#bound

As the docs say:

Schemars does not use trait bounds from #[serde(bound)] attributes.

This is because in many cases, the bounds needed for De/Serialize would be different to the bounds needed for JsonSchema.

So in your case, you would need to add #[schemars(bound = "A: Sized")]

However, a nice enhancement would be to improve the automatically-generated bounds to be smarter, e.g. ignore PhantomData fields. This wouldn't be easy, but is certainly possible - and fortunately can mostly be done by copying what serde does 😄

[GREsau]

I just noticed that I'd already created an issue for improving automatic trait bounds (#168) so I'll close this in favour of that