feature request: JSON schema support via https://github.com/GREsau/schemars

[yazshel]

Hi,

I'm keen to use rust-decimal in my rust/rocket web apps which utilise the rocket-okapi, okapi and schemars to produce OpenAPI/Swagger API specifications. Supporting this basically requires adding impls: impl schemars::JsonSchema for rust_decimal::Decimal but will likely require different impls depending on the selected serde feature (eg. providing a JSON string schema with regex for the serde-str option).

I'm open to doing some work on this but thought I'd check in to see if there were any ideas on how best to implement this in a manner consistent with to existing serde support.

One challenge is that schemars doesn't support #[serde(with = <mod>)]-style macros. However, these could be supported through adding dummy "schema" structs for relevant serde features and explicitly referring to these with #[schemars(with = <struct>)] decorators.

For example:
in rust_decimal::schemars.rs:

pub struct DecimalWithAbitraryPrecision {}

impl JsonSchema for DecimalWithAbitraryPrecision {
  <implement JsonSchema functions specific to abitrary_precision feature>
}

Then in relevant application code:

#[derive(Serialize, Deserialize, JsonSchema)]
pub struct MyApiObject {
    ...
    #[serde(with = rust_decimal::serde::abitrary_precision)] 
    #[schemars(with = rust_decimal::schemars::DecimalWithAbitraryPrecision)]
    my_decimal: rust_decimal::Decimal,
    ...
}

This is a bit clunky but was the best I could come up with. Any better ideas about how to implement such support?

[Tony-Samuels]

We're trying to decide the best way to approach this in general. E.g. #611.