Discriminator enum property breaks enum value

[alex-eri]

openapi-typescript version

7.13.0

Node.js version

v24.13.0

OS + version

Debian GNU/Linux 13 (trixie)

Description

If the schema declares a oneOf property with discriminator the generated Types will have their name as discriminator value and their value at same time. So generated type is always never.

Reproduction

Schema: https://yookassa.ru/developers/api/yookassa-openapi-specification.yaml

Generated type is never

        ConfirmationDataExternal: Omit<components["schemas"]["ConfirmationData"], "type"> & Record<string, never> & {
            /**
             * @description discriminator enum property added by openapi-typescript
             * @enum {string}
             */
            type: "ConfirmationDataExternal";
        } & {
            /**
             * @description discriminator enum property added by openapi-typescript
             * @enum {string}
             */
            type: "external";
        };

Expected result

        ConfirmationDataExternal: Omit<components["schemas"]["ConfirmationData"], "type"> & Record<string, never> & {
            /**
             * @description discriminator enum property added by openapi-typescript
             * @enum {string}
             */
            type: "external";
        };

Schema has issues, but not here.

    ConfirmationData:
      description: "Information required to initiate the selected payment confirmation scenario by the user. More about confirmation scenarios: https://yookassa.ru/developers/payment-acceptance/getting-started/payment-process#user-confirmation"
      type: "object"
      properties:
        type:
          $ref: "#/components/schemas/ConfirmationDataType"
        locale:
          $ref: "#/components/schemas/Locale"
      discriminator:
        propertyName: "type"
        mapping:
          redirect: "#/components/schemas/ConfirmationDataRedirect"
          external: "#/components/schemas/ConfirmationDataExternal"
          qr: "#/components/schemas/ConfirmationDataQr"
          embedded: "#/components/schemas/ConfirmationDataEmbedded"
          mobile_application: "#/components/schemas/ConfirmationDataMobileApplication"
      required:
      - "type"

....

    ConfirmationDataType:
      description: "Type of payment confirmation scenario by the user. Possible values: redirect - redirecting the user to a ready-made YooMoney page or a partner's page; external - waiting for the user to confirm the payment independently; qr - generating a QR and displaying it on the payment page so that the user can confirm the payment; embedded - displaying the YooMoney payment widget; mobile_application - redirecting the user to the partner's payment app."
      type: "string"
      enum:
      - "redirect"
      - "external"
      - "qr"
      - "embedded"
      - "mobile_application"

....

    ConfirmationDataExternal:
      type: "object"
      allOf:
      - $ref: "#/components/schemas/ConfirmationData"
      - type: "object"

Required

• My OpenAPI schema is valid and passes the Redocly validator (npx @redocly/cli@latest lint)

Extra

• I’m willing to open a PR (see CONTRIBUTING.md)