JSON Schema const on direct schema properties is silently ignored

[aranw]

When a schema property uses the JSON Schema const keyword directly, the codegen silently drops the constraint and generates a plain field with no indication of the fixed value.

const is a JSON Schema keyword (draft-06+) that OpenAPI adopted when 3.1 aligned its Schema Object with JSON Schema draft 2020-12. The codegen only recognises const inside the oneOf-of-consts enum idiom — it never reads schema.Const from a direct property schema.

This affects any OpenAPI 3.1+ spec. The reproducing example below uses 3.2 but the behaviour is identical with openapi: "3.1.0".

Reproducing Spec

openapi: "3.2.0"
components:
  schemas:
    ResourceNotFound:
      type: object
      required: [type, title, status]
      properties:
        type:
          type: string
          const: https://example.com/errors/resource-not-found
        title:
          type: string
          const: Resource Not Found
        status:
          type: integer
          const: 404

What is currently generated

type ResourceNotFound struct {
    Type   string `json:"type"`
    Title  string `json:"title"`
    Status int    `json:"status"`
}

The const values are silently dropped. Nothing in the generated code enforces or reflects the fixed values.

What should be generated

At minimum, the constant values should be preserved as named Go constants and the fields should be initialised via something like ApplyDefaults()?. Ideally the struct gets a constructor that pre-populates them:

const (
    ResourceNotFoundType   = "https://example.com/errors/resource-not-found"
    ResourceNotFoundTitle  = "Resource Not Found"
    ResourceNotFoundStatus = 404
)

type ResourceNotFound struct {
    Type   string `json:"type"`
    Title  string `json:"title"`
    Status int    `json:"status"`
}

func (s *ResourceNotFound) ApplyDefaults() {
    s.Type   = ResourceNotFoundType
    s.Title  = ResourceNotFoundTitle
    s.Status = ResourceNotFoundStatus
}

I have a rough idea about a fix for this and up for attempting if you are accepting contributions?