Add caution on export rule

[komi1230]

Hello,

Thank you for developing such an awesome project.
I'm developing an application with Rust and Axum and I've found this crate is very helpful for documenting API spec.

When I started to use utoipa, I was stuck in how to export handler function since I put the handler function in different file and exported this.
And finally I solved this with exporting a function named with __path_ suffix.

When developing a big project, many people can split modules and cut off handler function in different file.
So I think this message would be very helpful for those people.

Thank you checking !

[juhaku]

Yeah, indeed, the handler with path macro and essentially the __path_ prefixed struct implementing the path for the handler need to be visible to the OpenApi trait to register them. There is planned effort to improve this a bit for bigger projects wherein people tend to split the functionality to separate modules. By allowing users to define multiple OpenApi trait implementing structs and merge them in root level. This way developers only need to export the struct to the root and can leave the implementation private to the module.

There already are people doing so but currently there is no built in support for this. There is an existing discussion related to this might be worth linking here: #208

[juhaku]

This is 👌 Just a minor edit to the text 🙂

[juhaku]

Awesome 👍

[komi1230]

Thank you for quick review !

[juhaku]

Thank you for quick review !

Anytime 🙂