Support custom `format` types.

[abemedia]

Description

I'd like to propose adding support for custom format types. These could come from the configuration. Maybe something like the following example:

generator:
  formats:
    decimal: github.com/shopspring/decimal.Decimal

This would result in a field with format: decimal to be of the type decimal.Decimal from the package github.com/shopspring/decimal.

Alternatively, we could implement this as an extension e.g.

type: string
x-ogen-type: github.com/shopspring/decimal.Decimal

We can implement some checks to ensure the package is importable, as well as checking that the type implements one of the following interfaces:

interface {
  Encode(e *jx.Encoder)
  Decode(d *jx.Decoder) error
}

interface {
  json.Marshaler
  json.Unmarshaler
}

interface {
  encoding.TextMarshaler
  encoding.TextUnmarshaler
}

Based on which of the interfaces it implements we can use a different template for encoding and decoding the value.

I'm happy to implement this feature, just wanted to first check if such a feature would be accepted and get alignment on the way it's configured.

[tdakkota]

I'm happy to implement this feature, just wanted to first check if such a feature would be accepted and get alignment on the way it's configured.

It would be nice. This feature was requested before.

I think it is better to configure it via extension x-go-type, since it also used by oapi-codegen and go-swagger.

[abemedia]

Thanks for getting back to me on this @tdakkota!

Both oapi-codegen and go-swagger use different formats though:

oapi-codegen

x-go-type: googleuuid.UUID
x-go-type-import:
  path: github.com/google/uuid
  name: googleuuid

go-swagger

x-go-type:
  import:
    package: github.com/google/uuid
    alias: googleuuid
  type: UUID

I personally still prefer the idea of writing a single field e.g.

x-go-type: github.com/google/uuid.UUID

We could also automatically alias it if there's a clash between package names.

What's your preference?

[tdakkota]

I personally still prefer the idea of writing a single field e.g.

x-go-type: github.com/google/uuid.UUID

Me too. I didn't notice that oapi-codegen requires a x-go-type-import. In that case, let's keep it x-ogen-type.