Enhance validation error feedback for endpoint requests about poem HOT 3 OPEN

FastAPI returns a Json body that looks like this:

{
    "detail": [
        {
            "loc": [
                "path",
                "item_id"
            ],
            "msg": "value is not a valid integer",
            "type": "type_error.integer"
        }
    ]
}

I find this super handy because the response tells you all your validation errors in the request, not just the first one it hit.
It would be good if the bad_request_handler got a vec of validation errors rather than a single error. This would then allow one to produce a similar response.

from poem.

You can define a bad_request_handler to create a response for the error, refer to this example to implement it. 🙂

When the request parsing fails, it may be of these types.

from poem.

I'd love to have the ability to list all validation errors in a formalized manner. This is a future I widely use in other frameworks to tell the client exactly why the request is bad. Comes in handy in frontend - to paint invalid form fields red and add hints to them.

Maybe add a validation_errors_handler, similiar to bad_request_handler, that would accept a vec of validation errors and return a #[derive(Object)] struct?

Should I issue a separate feature request for this?

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