Consider representing multiple types in 3.0 using anyOf or oneOf

[Youssef1313]

See dotnet/aspnetcore#66304 for context.

[baywet]

Hi Youssef Fahmy (@Youssef1313)
Thank you for using the SDK and for reaching out.

An issue like this one that only links into a downstream issue has limited helpfulness. It requires building a lot of additional context, some of which is not relevant to the current repository.

What would be more helpful would be to share a reproduction, using this repository's code only. From reading the downstream issue, it's not clear why should such normalization be in in this library? One could argue it's application specific.

Let me know if you have any additional comments or questions.

[Youssef1313]

Basically:

            var schema = new OpenApiSchema();
            schema.Type = JsonSchemaType.String | JsonSchemaType.Integer;
            var s = await schema.SerializeAsJsonAsync(OpenApiSpecVersion.OpenApi3_0);

Because OpenAPI 3.0 doesn't support multiple types, but it supports oneOf, the user is requesting to re-write this using oneOf or anyOf which are supported by 3.0.

The above serializes as empty schema today, which matches everything.

Note that the request here isn't limited to when only Type is specified. If there are other properties that are specified they should be emitted as well.

The open question here is what to do in case the user already have specified both anyOf and oneOf, in which case there is not easy place for us to emit the types without doing more crazy re-writing. But we could decide to keep the current behavior in this specific case.

I don't know how you would feel about writing multiple types as oneOf/anyOf though. It's a small rewriting that I think should always produce an equivalent schema, so probably worth doing.