Using class-based views with Flask 2.2 causes TypeError: view() takes 0 positional arguments but 1 was given

[NimaQu]

Error when using class-based views for compliance documentation

from flask.views import MethodView
from apiflask import APIFlask

app = APIFlask(__name__)


@app.route('/pets/<int:pet_id>', endpoint='pet')
class Pet(MethodView):

    def get(self, pet_id):
        return {'message': 'OK'}

    def delete(self, pet_id):
        return '', 204

app.run(debug=True)

Environment:

• Python version: 3.10
• Flask version: 2.2.2
• APIFlask version: 1.1.2

[hjlarry]

I compare the source code of dispatch_request() in flask and apiflask.
It seems this example class based routes only accepts keyword arguments.
The flask always return view_function(**req.view_args).
But for apiflask, I don't know why it return view_function(*req.view_args.values()) for most situation

[greyli]

The change in pallets/flask#4624 (Flask 2.2) caused this issue. Before 2.2, the view function created by view classes accepts both positional arguments and keyword arguments. 2.2 changed to accept keyword-only arguments, while APIFlask always passes request.view_args as positional arguments to make sure the arguments passed to the view function are in natural order (docs).

Pin Flask to 2.1 will fix this temporarily:

pip install flask==2.1

[greyli]

I just released 1.1.3 to pin Flask < 2.2 as a temporal workaround for this issue. For the real fix to this issue, these are the possible solutions:

0. Revert this change upstream (Re-add *args to the view function in View classes pallets/flask#4776).
1. Patch the view function in our add_url_rule method. Not sure how to do this. Maybe the Python signature can do the trick.
2. Copy the whole flask.view module and modify it. This will be a breaking change (for class-based view users) since the user has to change the import statement from from flask.views import MethodView to from apiflask.views import MethodView. And we have to mirror future changes for this module from Flask.
3. Turn all the arguments passed to the view function into keyword arguments (proposed by davidism). This seems a clean solution since we can remove the patched APIFlask.dispatch_request. This is also a breaking change that will affect all users. We have to set a default keyword for input data from different locations (data for JSON or json for JSON?). Users have to pass an argument to the app.input decorator to use a different argument name.

I prefer solution 1 now, while solution 3 seems a better option for the long term.

[hjlarry]

It seems solution 1 can compat with current user project, 2 and 3 are both broken change.
I think we can try whether solution 1 worked first, 2 and 3 we can concern for the next big version.
But I don't know how to patch a function.