[BUG] model not generated when schema only referenced in parameters section

When a schema is referenced only in the parameters section, that referenced model is not generated.

openapi-generator version

7.12.0

I am not sure it is a regression, I've not been following the releases closely.

OpenAPI declaration file content or url

---
openapi: 3.0.0
info:
  title: Pet
  version: v1

paths:
  /cats:
    parameters:
      - name: name
        in: query
        schema:
          type: string
      - name: age
        in: query
        schema:
          $ref: "#/components/schemas/age"
    get:
      description: get found cats
      responses:
        '200':
          description: cats
          content:
            application/json:
              schema:
                type: string

components:
  schemas:
    age:
      enum: [ BABY, YOUNGSTER, OLDY ]

Generation Details

Using the maven plugin to generate the code from the above definition

Steps to reproduce

When using the above yaml,

• it leads to a warning:

[WARNING] #/components/schemas/age is not defined

• the model file is written as an import in the pet.service.ts:

import { Age } from '../model/age';

• but no model file for the enum age is generated

leading to compile time issues pointing to a referenced model that is not present.

The "workaround" is to adjust the definition slightly, ("type: string" to the "$ref: ..."):

    get:
      description: get found cats
      responses:
        '200':
          description: cats
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/age"

Which has the effect that the age enum is referenced now also from beyond the parameters schema, and then:

• no warning is shown
• the import statement is still there
• the model file for age is generated

Then it works. But not in all cases in my definition the schema is referenced from other places then the parameters - so this workaround is not feasible in all cases.

I've seen this happening for generators typescript-angular as well as the jaxrs-spec - I've not tried out others - so I suspect it is not related to the generators themselves.

Related issues/PRs

Both https://github.com/OpenAPITools/openapi-generator/issues/4710 and https://github.com/OpenAPITools/openapi-generator/issues/1123 point to a probable cause where definitions are split over files, but I could also imagine that both of these issues are there because there is only a reference from the parameters, and not from anywhere else.

Reproduce the supplied OpenAPI YAML with the Maven plugin, comparing typescript-angular and jaxrs-spec generation as described. Trace how a schema referenced only from path-level parameters is discovered; done means the warning is gone and the referenced age enum model is generated alongside its existing import.