[FEATURE] Support customizing the generated OpenAPI JSON schema

[birgander]

After a discussion on softwaremill.community (https://softwaremill.community/t/differentiating-between-undefined-and-null/154/8), @adamw suggested opening an issue.

In short, this is a feature request for some way to customize what the generated OpenAPI JSON schema will be for a type.

In my particular use case, I needed the option to set "nullable" to true for a specific type, not for all optional types (that is already supported).

It is possible to manually, eg. with quicklens, modify the OpenAPI returned from OpenAPIDocsInterpreter(). toOpenAPI(...), but it's not very elegant.

Adam's suggestion from the discussion:

As for a more user-friendly fix, I think we should have an option to customise the final, generated JSON Schema (which is part of the OpenAPI object). We could set an attribute on the tapir-schema, with a function which would be called by the OpenAPI interpreter.

[jumale]

hi, I think I have a similar issue, I'll check the suggested workaround, but I also would like to mention my case here, to add it to the context: I have a Scala type List[Option[T]] let's say it's List[Option[Int]], which in JSON becomes [1, 2, null, 4] At the moment when deriving Schema[List[Option[Int]]] - it gets compiled into OpenAPI just as array<integer>, which then gets incorrectly interpreted by clients and results into runtime errors.

T.b.h. I'm not even 100% sure what's the right way to express it in the OpenAPI schema, but I think it's probably something like this:

UPDATE: I've achieved the expected result by injecting a key-word into the Schema[List[Option[T]]] (I used title for it) and then capturing this key-word in the generated OpenAPI and updating the schema with schema.items.nullable = true:

UPDATE 2: I've found out that there is OpenAPIDocsOptions.markOptionsAsNullable which already does the right job when switched to true.