duplicate-oneof-discriminator

Finds a discriminator value reused by multiple branches of the same oneOf.

Attribute	Value
Category	Schema
Maturity	Platinum
OpenAPI	Swagger 2.0; OpenAPI 3.0, 3.1, 3.2
Starter	Off
Lenient	Warning
Recommended–Complete	Error

Intent

A discriminator must identify one branch. Reused values make branch selection ambiguous.

Flags

A schema with discriminator.propertyName and at least two oneOf branches when the named property has the same const or enum value in more than one branch. Inline and referenced branches are inspected.

Does not flag

Unique values, schemas without both a discriminator and oneOf, or branches that do not constrain the discriminator with const or enum.

See it fail

Actor:
  discriminator:
    propertyName: kind
  oneOf:
    - type: object
      properties:
        kind:
          const: person
    - type: object
      properties:
        kind:
          const: person

Both branches claim person.

Fix it

Assign a distinct value to each branch:

Actor:
  discriminator:
    propertyName: kind
  oneOf:
    - type: object
      properties:
        kind:
          const: person
    - type: object
      properties:
        kind:
          const: company

For OpenAPI 3.0, express the single values as one-item enum arrays.

Configure

profiles:
  default:
    rules:
      extends: [recommended]
      override:
        duplicate-oneof-discriminator: warn

Nearby: spec-discriminator-defaultMapping, allof-contradictory-constraints.