Include exceptions in API documentation

They have to be declared here:

@app.get("/",responses={418: {"detail": "I'm a teapot"}, 413: {"Too large": "...The Payload"}})
def read_root(gimme_coffee: bool = False):
    if gimme_coffee:
        raise HTTPException(status_code=418, detail="I'm a teapot.")
    return {"Hello": "World"}

A hacky way from https://github.com/tiangolo/fastapi/issues/1999#issuecomment-735970673

A slight variation could work, if parameters were accepted, with string formatting.

from fastapi import status, HTTPException

class APIException(HTTPException):
    """Light wrapper around HTTPException that allows specifying defaults via class property"""

    status_code = status.HTTP_400_BAD_REQUEST
    detail = None
    headers = None

    def __init__(self, *args, **kwargs):
        if "status_code" not in kwargs:
            kwargs["status_code"] = self.status_code
        if "detail" not in kwargs:
            kwargs["detail"] = self.detail
        if "headers" not in kwargs:
            kwargs["headers"] = self.headers
        super().__init__(*args, **kwargs)

class TeapotException(APIException):
    status_code = 418
    detail = "I'm a teapot."

@app.get("/")
def read_root(gimme_coffee: bool = False, response_exceptions=[TeapotException]):
    if gimme_coffee:
        raise TeapotException()
    return {"Hello": "World"}

Start by examining the FastAPI route declaration using responses and the HTTPException examples in the issue. Determine how declared or class-based exceptions could be represented in the generated API documentation. Done means endpoint exceptions appear in the API documentation without relying on the proposed hack.