Use __wrapped__ attribute

[lucaswiman]

Fixes #5065 where the globalns computation in get_typed_signature misses an edge case handled by typing.get_type_hints. This PR makes the logic similar to get_type_hints.

Background

functools.wraps updates the annotations and type signature to match the wrapped function. However, it copies the __annotations__ dict verbatim, including forward references (strings). get_type_hints handles this by dereferencing the __wrapped__ attribute until it gets to the original function, then uses the __globals__ of that function.

Testing

I added a test case which reproduced the NameError seen in #5065. The test passes after my commit updating the implementation of get_typed_signature:

tests/test_wrapped_method_forward_reference.py:24:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
fastapi/routing.py:617: in decorator
    self.add_api_route(
fastapi/routing.py:556: in add_api_route
    route = route_class(
fastapi/routing.py:425: in __init__
    self.dependant = get_dependant(path=self.path_format, call=self.endpoint)
fastapi/dependencies/utils.py:279: in get_dependant
    endpoint_signature = get_typed_signature(call)
fastapi/dependencies/utils.py:249: in get_typed_signature
    typed_params = [
fastapi/dependencies/utils.py:254: in <listcomp>
    annotation=get_typed_annotation(param, globalns),
fastapi/dependencies/utils.py:266: in get_typed_annotation
    annotation = evaluate_forwardref(annotation, globalns, globalns)
pydantic/typing.py:76: in pydantic.typing.evaluate_forwardref
    ???
../../.pyenv/versions/3.9.1/lib/python3.9/typing.py:533: in _evaluate
    eval(self.__forward_code__, globalns, localns),
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

>   ???
E   NameError: name 'ForwardRef' is not defined

<string>:1: NameError
============================================================== short test summary info ===============================================================
FAILED tests/test_wrapped_method_forward_reference.py::test_wrapped_method_type_inference - NameError: name 'ForwardRef' is not defined
================================================================= 1 failed in 0.59s ==================================================================

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (cf73051) 100.00% compared to head (d293bb3) 100.00%. Report is 1038 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff            @@
##            master     #5077   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          540       541    +1     
  Lines        13969     13930   -39     
=========================================
- Hits         13969     13930   -39     

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[lucaswiman]

@tiangolo This PR has 3 approvals. Could you please merge this PR or comment about what additional steps I should take prior to merge? Thanks!

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[zachkirsch]

+1 I'd love for this to merge in!

[dsinghvi]

@tiangolo what would it take to get this merged in?

[dsinghvi]

@tiangolo following up again -- pr has 3 approvals, what can we do to get this in?

[ashwin153]

@tiangolo Would it be possible to get this merged?

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[zachkirsch]

@tiangolo is there anything is particular that is blocking this PR from merging?

[jochs]

@tiangolo hey! is there any way for me to help prioritize this getting in?

FWIW post 0.89 you also need to update get_typed_return_annotation to look like this:

    def get_typed_return_annotation(call: Callable[..., Any]) -> Any:
        signature = inspect.signature(call)
        annotation = signature.return_annotation

        if annotation is inspect.Signature.empty:
            return None

        nsobj = inspect.unwrap(call)
        globalns = getattr(nsobj, "__globals__", {})
        return get_typed_annotation(annotation, globalns)