allOf should accept Referenced Schema

[mossprescott]

According to the spec, a reference is allowed anywhere a Schema Object can appear, but _schemaAllOf :: Maybe [Schema] means that only an inline schema is accepted for the allOf property.

As far as I can tell, all other Schema properties are typed as Referenced Schema.

The motivating case is a schema which has several UTCTime properties, each with a different description, example, min, etc. our workaround for the time being is to inline the UTCTime schema each time it is used, but I believe allOf is a better way of representing this situation, and experimenting with hand-written swagger.json suggests that SwaggerUI handles it.

Note: I’d be happy to submit a PR changing the type, but it will break any code that uses allOf. Is there any guidance about how to introduce a change like this without too much disruption?

[fizruk]

Interestring, I did not think allOf could actually be useful!

Can you share more about the workflow you have (or would like to have) with allOf?

I know about the problem with different descriptions for different fields, but I do not have any good solutions. Except making newtypes with adjusted ToSchema instances (which is unfortunate if you only need to change the description). I think the problem is actually that Swagger does not allow descriptions for fields (not schemas), but that does not make our lives easier :)

I'm happy to accept a PR. I don't think many people use allOf, but it's not a huge change anyway.
People would just have to wrap their schemas in Inline for things to work as before.

[mossprescott]

Nice, thanks, @fizruk and @rodrigosetti!