Feature Request: support Open API's `discriminator` for discriminated union types

[mbylstra]

Open API supports discriminated union types (like oneOf, but the types narrow depending on the discriminator, which is usually a set of strings or an enum)

This is really helpful for generating type safe polymorphic APIs.

more info: https://apidog.com/blog/openapi-discriminator-guide/

[raphael]

That makes sense and the OpenAPI generation is pretty simple to do. The marshalling/unmarshalling code is a bit trickier to generate. I imagine there would have to be a DSL function to identify the discriminator field and then a way to represent the various possible variations: either a superset of all fields or embedded structs or... We may want to give the option to the user in the DSL. The generated code would then have to consult the field and initialize the right fields. I'd love to see a full-fledged proposal (similar to #3696).