Fixed signature of views decorated with signed_data_view

[spookylukey]

This fixes a nuisance when using django-debug-toolbar with django-urlconfchecks which type checks URLconfs, and possibly other tools. Otherwise it has little effect.

Basically, the @functools.wraps() call within the signed_data_view decorator makes views like sql_explain appear to have an external signature of sql_explain(request, verified_data) to tools like inspect.signature. If this was really the case, then the function would fail when used from the urlconf, because the verified_data parameter is not passed.

So, django-urlconfchecks raises an error for these views.

In reality signed_data_view is providing that argument, and so changing the effective signature of the function.

With the patch, the signature is changed to sql_explain(request, *args, **kwargs), which is not as accurate as it could be, but at least django-urlconfchecks now just issues a warning (about *args / **kwargs preventing signature checking), and not an error.

An alternative fix is to remove the @functools.wraps call entirely in the implementation of signed_data_view, but that would potentially produce more problems.

A test is added for this.

[matthiask]

Thank you! Looks good to me. I checked the functools.update_wrapper implementation and I think this makes sense. I don't know much about typechecking though so I'll wait for a moment before merging.

[tim-schilling]

I'm less sure about this. We're removing the attribute that's used to fetch the wrapped function. I can imagine that this will cause weirder issues than django-urlconfchecks down the line having a problem with this decorator pattern.

I'd prefer to see the debug toolbars url patterns excluded from evaluation or for us to rework this decorator so that it doesn't pass the verified data as an argument. Or pass it as a part of kwargs and hide it as an explicit keyword argument.

[tim-schilling]

@spookylukey can you confirm that #1658 resolves the issue with django-urlconfchecks please?

[spookylukey]

I did some research and found a package makefun to help create decorators that produce 100% correct signatures. With it, you would write something like:

@makefun.wraps(view, remove_args="verified_data") 

instead of @functools.wraps

https://smarie.github.io/python-makefun/#easier-edits

However, this adds a dependency and seems like overkill, unless django-debug-toolbar were itself adopting django-urlconfchecks for its own usage.

[tim-schilling]

Ah, that's pretty neat but I'd prefer to avoid adding additional dependencies to the project.

[spookylukey]

@spookylukey can you confirm that #1658 resolves the issue with django-urlconfchecks please?

Yes, I've checked and that works.

[tim-schilling]

Closing in favor of #1658