OpenAPI: Support for `const` values in string parameter types

[appleton]

What are the steps to reproduce this issue?

Given a schema like this:

     responses:
        "200":
          content:
            text/event-stream:
              schema:
                description: Each oneOf object in the array represents one possible Server Sent Events (SSE) message, serialized as UTF-8 text according to the SSE specification.
                items:
                  oneOf:
                    - properties:
                        data:
                          $ref: "#/components/schemas/ResponseError"
                        event:
                          const: error
                          description: The event name.
                          type: string
                        id:
                          description: The event ID.
                          type: integer
                        retry:
                          description: The retry time in milliseconds.
                          type: integer
                      required:
                        - data
                        - event
                      title: Event error
                      type: object
                    - properties:
                        data:
                          $ref: "#/components/schemas/ResponseData"
                        event:
                          const: data
                          description: The event name.
                          type: string
                        id:
                          description: The event ID.
                          type: integer
                        retry:
                          description: The retry time in milliseconds.
                          type: integer
                      required:
                        - data
                        - event
                      title: Event data
                      type: object

What happens?

My schema types actually look like this:

export type Response200ItemOneOf = {
  data: ResponseError;
  /** The event name. */
  event: string;
  /** The event ID. */
  id?: number;
  /** The retry time in milliseconds. */
  retry?: number;
};

export type Response200ItemOneOfTwo = {
  data: ResponseData;
  /** The event name. */
  event: string;
  /** The event ID. */
  id?: number;
  /** The retry time in milliseconds. */
  retry?: number;
};

What were you expecting to happen?

For my schema types to look like this. Note that the event property is restricted to only the const value (error or data).

export type Response200ItemOneOf = {
  data: ResponseError;
  /** The event name. */
  event: "error";
  /** The event ID. */
  id?: number;
  /** The retry time in milliseconds. */
  retry?: number;
};

export type Response200ItemOneOfTwo = {
  data: ResponseData;
  /** The event name. */
  event: "data";
  /** The event ID. */
  id?: number;
  /** The retry time in milliseconds. */
  retry?: number;
};

Any other comments?

I guess that either const isn't supported or maybe I'm just doing something wrong?

What versions are you using?

Operating System: MacOS 14.4.1 Package Version: 6.27.1 Browser Version: N/A

[melloware]

But isn't that what const means? What were you expecting in the output?

[appleton]

Specifically I'm expecting my event fields to look like this:

  event: "data";
// and
  event: "error";

but they actually look like this:

  event: string;
// and
  event: string;

[mortezakarimi]

@appleton I think you should define event as enum to get expected result

https://swagger.io/docs/specification/data-models/enums/

      responses:
        "200":
          content:
            text/event-stream:
              schema:
                description: Each oneOf object in the array represents one possible Server Sent Events (SSE) message, serialized as UTF-8 text according to the SSE specification.
                items:
                  oneOf:
                    - properties:
                        data:
                          $ref: "#/components/schemas/ResponseError"
                        event:
                          enum:
                            - error
                            - data
                          description: The event name.
                          type: string
                          default: 'error'
                        id:
                          description: The event ID.
                          type: integer
                        retry:
                          description: The retry time in milliseconds.
                          type: integer
                      required:
                        - data
                        - event
                      title: Event error
                      type: object
                    - properties:
                        data:
                          $ref: "#/components/schemas/ResponseData"
                        event:
                          enum:
                            - error
                            - data
                          description: The event name.
                          type: string
                          default: 'data'
                        id:
                          description: The event ID.
                          type: integer
                        retry:
                          description: The retry time in milliseconds.
                          type: integer
                      required:
                        - data
                        - event
                      title: Event data
                      type: object

[appleton]

Hi @mortezakarimi thanks for the suggestion. It's better but it doesn't quite give me the result I'm after:

export const PromptModel200ItemOneOfThreeEvent = {
  error: 'error',
  data: 'data',
} as const;

export type Response200ItemOneOf = {
  data: ResponseError;
  /** The event name. */
  event: PromptModel200ItemOneOfThreeEvent;
  /** The event ID. */
  id?: number;
  /** The retry time in milliseconds. */
  retry?: number;
};

export type Response200ItemOneOfTwo = {
  data: ResponseData;
  /** The event name. */
  event: PromptModel200ItemOneOfThreeEvent;
  /** The event ID. */
  id?: number;
  /** The retry time in milliseconds. */
  retry?: number;
};

What I want to be able to do in my application code is have a succinct way to type switch on the objects and one way to do that (if I had the output I was expecting from the const declaration) would be:

// response is a Response200ItemOneOf | Response200ItemOneOfTwo
switch(response.event) {
  case "error":
    // response is now a Response200ItemOneOf
  break;
  case "data":
    // response is now a Response200ItemOneOfTwo
  break;
}

[RinseV]

I ran into this as well and tried to fix it in #1376 but it seems that the const keyword is supported, as long as you don't combine it with a type. Having a property defined as:

constant:
  type: string
  const: something

is generated as

constant: string;

while a property defined as:

constant:
  const: something

is generated as

constant: "something";

I'm not sure if this is a valid specification, it might be that type should always be specified, but it does solve the problem for me.