b.yaml

openapi: 3.0.0
info:
  title: ""
  version: ""
servers:
  - url: /
paths:
  /api/foo:
    get:
      responses:
        200:
          description: ""
          content:
            application/json;charset=utf-8:
              schema:
                $ref: "#/components/schemas/Bad"
components:
  schemas:
    Bad:
      allOf:
        - $ref: "#/components/schemas/Bad"