a.yaml

components:
  schemas:
    A:
      type: object
      properties:
        bar:
          $ref: "#/components/schemas/B"
    B:
      anyOf:
        - $ref: "#/components/schemas/B"
      type: object
openapi: 3.0.0
info:
  version: ""
  title: ""
paths:
  /foo:
    get:
      responses:
        "200":
          content:
            application/json;charset=utf-8:
              schema:
                $ref: "#/components/schemas/A"
          description: ""