Referenced nullable object types are not generated as possibly null

[raphael-verdier]

Describe the bug

Referenced nullable objects are not correctly generated as either an object or null.

Considering those two schemas that should result in the same typing:

NullableObject:
  type: object
  nullable: true
  description: An object that can be null.
  properties:
    testProperty:
      type: string

CoreObjectBug:
  type: object
  properties:
    referenceA:
      $ref: '#/NullableObject'


CoreObjectWorkaround:
  type: object
  properties:
    referenceA:
      type: object
      nullable: true
      description: An object that can be null.
      properties:
        testProperty:
          type: string

The generated type for NullableObject is the following, which is wrong:

export type NullableObject = {
    testProperty?: string;
};

The generated type for CoreObjectWorkaround is the following, which is correct:

export type CoreObjectWorkaround = {
    /**
     * An object that can be null.
     */
    referenceA?: {
        testProperty?: string;
    } | null;
};

This bug is isolated to referenced object types as I use referenced atomic nullable types that don't have this bug.

[mrlubos]

@raphael-verdier if you're able to submit a failing test case to our fork, I might have a look at this for you

[raphael-verdier]

@mrlubos If I have some time I will try to do it but I never looked at the source code

[mrlubos]

@raphael-verdier can you try generating your client with our fork? It's possible it may even work, I haven't tested this scenario myself.

For failing test case, here's an example. I'd need a schema in test/spec/v3.json (like you have in the issue description), and then the expected types in the snapshot. If the generator produces incorrect code, that snapshot should fail during tests, you can leave that as a draft pull request, and I'd take it from there

[mrlubos]

@raphael-verdier this is fixed in @nicolas-chaulet/openapi-typescript-codegen, give it a try!