Checking responders signatures

[jkmnt]

I propose adding check if responder arguments match the template fields. Now it's easy to introduce error by renaming
arguments while refactoring.

Since this feature is likely to use the heavy inspect module, it may be implemented in inspect_app, which
imports it anyway. Then inspect_app will additionally emit warnings if arguments mismatch.
Also for type-annotated arguments it may be useful to check if type matches the field converter type.

fields = get_route_fields()
responder = get_route_responder()

req, resp, *args  = inspect.signature(responder).values()

for field, arg in zip(fields, args):
    check_arg(field, arg)
    check_anno(field, arg.annotation)

[CaselIT]

Hi,

I think this feature makes sense.
I think it may be done while adding the routes by the router (or the app), since that's is an "offline" phase where it's likely fine to execute a few more operations to check that everything works correctly.

This could probably be a configuration in the router config (or the app config?) where we have something like off | warn | error (maybe log too??). The default would likely be warn

[vytas7]

For the annotations part, see also #2408 that I've just filed.