[BUG] openapi-yaml generator produces invalid output with nested references

Description

When using the structure described below as input to the openapi-yaml generator, the output is incorrect. The generation does not fail per se, but the output is malformed. There are multiple error messages

Failed to get the schema name

and

Error obtaining the datatype from ref

in the log, pointing to the cause of the problem.

openapi-generator version

Tested using the openapi-generator-cli Docker v7.24.0.
This does not appear to constitute a regression.

Expected vs. Actual

The difference is on the schemata for ArrayOfComplexTypes and NullableComplexType.

Actual:

openapi: 3.0.4
info:
  title: Open API Ref Test
  version: "1.0"
servers:
- url: /
paths:
  /simple:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/SimpleType"
          description: Simple return
  /arr:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/ArrayOfComplexTypes"
          description: description
  /null:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/NullableComplexType"
          description: description
components:
  schemas:
    ComplexType:
      properties:
        prop1:
          $ref: "#/components/schemas/SimpleType"
        prop2:
          items:
            $ref: "#/components/schemas/SimpleType"
          type: array
        prop3:
          allOf:
          - $ref: "#/components/schemas/SimpleType"
          nullable: true
      type: object
    SimpleType:
      example:
        value: value
      properties:
        value:
          type: string
      type: object
    ArrayOfComplexTypes:
      example:
        complexArray:
        - "{}"
        - "{}"
      properties:
        complexArray:
          items:
            $ref: ./swagger.yml#/components/schemas/ComplexType
          type: array
      type: object
    NullableComplexType:
      example:
        complexOrNull: ""
      properties:
        complexOrNull:
          allOf:
          - $ref: ./swagger.yml#/components/schemas/ComplexType
          nullable: true
      type: object

Expected:

openapi: 3.0.4
info:
  title: Open API Ref Test
  version: "1.0"
servers:
- url: /
paths:
  /simple:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/SimpleType"
          description: Simple return
  /arr:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/ArrayOfComplexTypes"
          description: description
  /null:
    get:
      responses:
        "200":
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/NullableComplexType"
          description: description
components:
  schemas:
    ComplexType:
      properties:
        prop1:
          $ref: "#/components/schemas/SimpleType"
        prop2:
          items:
            $ref: "#/components/schemas/SimpleType"
          type: array
        prop3:
          allOf:
          - $ref: "#/components/schemas/SimpleType"
          nullable: true
      type: object
    SimpleType:
      example:
        value: value
      properties:
        value:
          type: string
      type: object
    ArrayOfComplexTypes:
      example:
        complexArray:
        - "{}"
        - "{}"
      properties:
        complexArray:
          items:
            $ref: "#/components/schemas/ComplexType"
          type: array
      type: object
    NullableComplexType:
      example:
        complexOrNull: ""
      properties:
        complexOrNull:
          allOf:
          - $ref: "#/components/schemas/ComplexType"
          nullable: true
      type: object

OpenAPI declaration file content or url

DIrectory structure:

swagger.yml:

openapi: 3.0.4
info:
  version: "1.0"
  title: Open API Ref Test
paths:
  '/simple':
    get:
      responses:
        '200':
          description: Simple return
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/SimpleType'
  '/arr':
    get:
      responses:
        '200':
          description: description
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ArrayOfComplexTypes'
  '/null':
    get:
      responses:
        '200':
          description: description
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/NullableComplexType'

components:
  schemas:
    ComplexType:
      $ref: "./schemas/ComplexType.yml"
    SimpleType:
      $ref: "./schemas/SimpleType.yml"
    ArrayOfComplexTypes:
      $ref: "./schemas/ArrayOfComplexTypes.yml"
    NullableComplexType:
      $ref: "./schemas/NullableComplexType.yml"

schemas/SimpleType.yml

type: object
properties:
  value:
    type: string

schemas/ComplexType.yml:

type: object
properties:
  prop1:
    $ref: '../swagger.yml#/components/schemas/SimpleType'
  prop2:
    type: array
    items:
      $ref: '../swagger.yml#/components/schemas/SimpleType'
  prop3:
    nullable: true
    anyOf:
      - $ref: '../swagger.yml#/components/schemas/SimpleType'

ArrayOfComplexTypes.yml:

type: object
properties:
  complexArray:
    type: array
    items:
      $ref: '../swagger.yml#/components/schemas/ComplexType'

NullableComplexType.yml:

type: object
properties:
  complexOrNull:
    nullable: true
    anyOf:
      - $ref: '../swagger.yml#/components/schemas/ComplexType'

Generation Details

Steps to reproduce

Using the input described above, execute
docker run --rm -it --user $(id -u):$(id -g) --volume "${PWD}:/local" openapitools/openapi-generator-cli:v7.24.0 generate -g openapi-yaml -i local/swagger.yml -o local/out

Start by running the provided Docker command with swagger.yml and the four files under schemas/ to reproduce the malformed openapi-yaml output and logged errors. Compare the generated schemas for ArrayOfComplexTypes and NullableComplexType with the expected YAML; done means their external references resolve to the local #/components/schemas/ComplexType reference without errors.