Proposal: infer obvious parameters and return types #10149
Description
Feature
Similar to #4409, but also broader, allow for mypy to infer the parameter and return types for a function that's a passthrough to other typed functions.
Pitch
Consider the case in keyring, where the get_password function is a convenience accessor to (a) resolve the backend and (b) invoke the method of the same name on that backend with the same parameters:
The get_keyring() is annotated and always returns a KeyringBackend. KeyringBackend is annotated and its get_password always demands str parameters and declares its return type.
As a result, it's unambiguous what the required parameters and return type for core.get_password must be.
In pypa/twine#733, we learned that if a downstream consumer of the library enables disallow_untyped_calls, it will fail on core.get_password unless that function is redundantly decorated with the same parameters and return types of KeyringBackend.get_password.
It would be nice if mypy could infer the types from these unambiguous cases like passthrough functions, possibly gated by a feature flag or a decorator on the function (e.g. @typing.passthrough), and avoid the somewhat messy redundancy that results from hand-copying the types.