feat: add support for discriminator

[marikaner]

This provides an initial implementation for the discriminating properties of OpenAPI specs: https://swagger.io/docs/specification/data-models/inheritance-and-polymorphism/

According to the documentation this can only happen on oneOf and anyOf schemas and there can either be an explicit mapping or it is implicitly derived from the referenced schema names.

Of course, the Azure OpenAPI spec does not use oneOf but type: object.
Also, the Azure OpenAPI spec has a circular reference like:

- SchemaA:
  discriminator:
    propertyName: discriminatorProp
    mapping:
      value1: => SchemaB
      value2: => SchemaC
- SchemaB:
  allOf:
    - SchemaA // this references back to the original type
    - ...

This would result in something like this:

type SchemaA = { discriminatorProp: 'value1'} & SchemaB;
type SchemaB = SchemaA & ... // <-- ERROR

To solve this I added a post parsing sanitization step that checks explicitly for oneOf schemas with discriminator mapping and child schemas with allof mapping for circular refs.

TODO:

• Add test cases to test services
• Add docs

[MatKuhr]

I might not fully understand this test, but I think it should be:

Suggested change

	SchemaA: { properties: { c: { type: 'string' } } },
	SchemaB: { properties: { c: { type: 'integer' } } }
	SchemaA: { properties: { discriminatingProperty: { type: 'string' }, c: { type: 'string' } } },
	SchemaB: { properties: { discriminatingProperty: { type: 'string' }, c: { type: 'integer' } } }

The discriminator has to be a property of all schemas.

It is important that all the models mentioned below anyOf or oneOf contain the property that the discriminator specifies.

Don't ask me why this redundancy is necessary, IDK 😄
I guess it would also be possible for it to have different types, e.g. a string in SchemaA and a number in SchemaB.

Unfortunately, after checking again, the Azure spec seems to simply use this discriminator incorrectly. If you look at it in the swagger editor you can see that it is simply ignored and the type of the messages array is incorrect 😬

[MatKuhr]

Actually, they fixed this in the preview 2024-08-01, ... but stopped using the discriminator 🙃

[marikaner]

Oh damn, good catch. I read this multiple times yesterday, but still ignored it ;)
Unfortunately that makes things quite a bit more complicated, but let's see.

[marikaner]

ok, it doesn't make it more complicated. types should still work as expected.

[jjtang1985]

5 cases with discriminator: detected from the new spec, where 2 of them are not relevant (onYourData...)

Would it be ok to:

1. merge Deeksha's PR first.
2. use the Cloud SDK generator on a branch for fixing the AI SDK

With that:

• we dont even need a release from Cloud SDK
• we see smaller PR only related to discriminator

I would expect the version 2024-08-01 should have been released or soon in the future, by checking the name.