[BUG] [Swift5] support for oneOf, anyOf, allOf, and discriminator directives

Created by: lightman73

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output? The generated code should support the oneOf, anyOf, allOf directives

Description

If one has a response type defined as :

responses:
    '200':
        content:
            application/json:
                schema:
                    oneOf:
                        - $ref: '#/schemas/someObject1'
                        - $ref: '#/schemas/someObject2'

the generated Swift client has this requestBuilder definition:

let requestBuilder: RequestBuilder<OneOfsomeObject1someObject2>.Type = YourAPI.requestBuilderFactory.getBuilder()

but there is no trace of the OneOfsomeObject1someObject2 type definition in the generated code, thus making it not working.

Is there any way to get a working client for an openApi definition that uses oneOf (or anyOf, allOf) ?

openapi-generator version

5.0.0-SNAPSHOT, compiled from git.

Generation Details

openapi-generator generate -I defs.yaml -g swift5 ./output_dir

Related issues/PRs

https://github.com/OpenAPITools/openapi-generator/issues/2588#issue-429102544 (really old one, possibly relating to the old Swift 4 generator, gives a little suggestion, but not much)

@jgavris @ehyche @Edubits @jaz-ah @4brunu could one you look into the issue and see if there is any way to solve it ? Even a simple idea to point me in the right direction to implement the missing feature would be great...