[REQ] support for "const" keyword

[jorgerod]

Description

OpenAPI's Schema Object for OAS 3.1 to use JSON Schema 2019-09, which includes the const keyword (In this PR: Defining constant value in response the introduction of this keyword was discussed)

Describe the solution you'd like

The OpenAPI Spec would looks like:

components:
  schemas:
    UserBody:
      type: object
      properties:
        kind:  
          type: string
          const: MyConstant
        id:
          type: integer
        firstName:
          type: string
        lastName:
          type: string

Generated source:

public class UserBody {
    public final Static String KIND = "MyConstant"
     //...

}

Describe alternatives you've considered

IMHO, define an enum attribute with a single value in the list is not the same.

Related issues

#1916

[jorgerod]

Hi @jmini @wing328
How do you see it? I could even contribute it myself

[jbezuk]

Hello, maybe this is an okay place to bring up the question of general OAS 3.1 support? Another feature of 3.1 that brought me to this post was making the paths property optional, so that you can use a file to describe only, for example, reusable components. Currently the workaround is to use version 3 and turn off spec validation.
https://github.com/OAI/OpenAPI-Specification/releases/tag/3.1.0-rc0

[jorgerod]

Hi @jmini @wing328
How do you see it? I could even contribute it myself