Fail to load openapi.json when mounting API as sub application

[beenje]

I'd like to mount my versioned API under /api.

from typing import List
from fastapi import FastAPI, APIRouter
from pydantic import BaseModel

from fastapi_versionizer.versionizer import Versionizer, api_version


class User(BaseModel):
    id: int
    name: str


class UserV2(BaseModel):
    id: int
    name: str
    age: int


db = {
    'users': {}
}
app = FastAPI(
    title='test',
    redoc_url=None
)

users_router = APIRouter(
    prefix='/users',
    tags=['Users']
)


@app.get('/status', tags=['Status'])
def get_status() -> str:
    return 'Ok'


@api_version(1)
@users_router.get('', deprecated=True)
def get_users() -> List[User]:
    return list(user for user in db['users'].values() if isinstance(user, User))


@api_version(1)
@users_router.post('', deprecated=True)
def create_user(user: User) -> User:
    db['users'][user.id] = user
    return user


@api_version(2)
@users_router.get('')
def get_users_v2() -> List[UserV2]:
    return list(user for user in db['users'].values() if isinstance(user, UserV2))


@api_version(2)
@users_router.post('')
def create_user_v2(user: UserV2) -> UserV2:
    db['users'][user.id] = user
    return user

# Sub application for the API
original_api = FastAPI()
original_api.include_router(users_router)
app.mount("/api", original_api)

versions = Versionizer(
    app=original_api,
    prefix_format='/v{major}',
    semantic_version_format='{major}',
    latest_prefix='/latest',
    sort_routes=True
).versionize()

With this example:

• /docs works and shows GET /status as expected.
• /api/docs works and shows both v1 and v2 endpoints
• /api/v2/docs returns Failed to load API definition. It's trying to load /v2/openapi.json instead of /api/v2/openapi.json.