Support for postponed annnotations

[haizaar]

Consider main.py:

from __future__ import annotations
import functions_framework
import flask


class HelloRequest:
    name: str

    def __init__(self, name: str) -> None:
        self.name = name

    @classmethod
    def from_dict(cls, d: dict) -> HellowRequest:
        return cls(**d)

    def to_dict(self) -> dict:
        return self.__dict__


@functions_framework.typed
def hello(hr: HelloRequest) -> flask.typing.ResponseReturnValue:
    return f"Hello, {hr.name}"

Running import main yields:

input_type=HelloRequest, type(input_type)=<class 'str'>
Traceback (most recent call last):
  File "/home/....venv/lib/python3.11/site-packages/functions_framework/_typed_event.py", line 37, in register_typed_event
    _validate_input_type(input_type)
  File "/home/.../.venv/lib/python3.11/site-packages/functions_framework/_typed_event.py", line 103, in _validate_input_type
    raise AttributeError(
AttributeError: The type HelloRequest does not have the required method called  'from_dict'.

The culprit is from __future__ import annotations, which is required to annotate from_dict properly.

The issue is here where inspect.signature will return annotations as strings (by default) if they are postponed.

The suggested solution is to pass eval_str=True when calling inspect.signature.