lru_cache preserves signature of wrapped function

[Tomaz-Vieira]

This PR uses ParamSpec to make lru_cache preserve the signature of the wrapped function.

Unfortunately this removes the constraint that *args and **kwargs must be Hashable at least until the meaning of the bound parameter in ParamSpec is decided, but I feel that preserving the function signature is a worthy trade-off.

[Tomaz-Vieira]

So it seems mypy doesn't support ParamSpec yet. Could anyone point me to the correct course of action here? Should I just wait until it does?

[srittau]

You can # type: ignore the affected lines for now.

[srittau]

Thanks!

For future reference: Please don't force push, we squash on merge, but force pushing makes reviewing harder.

[srittau]

I'm not sure why pytype complains. Maybe @rchen152 has some insight.

[srittau]

The new primer warnings are probably due to the missing ParamSpec support in mypy and can be ignored.

[srittau]

@Tomaz-Vieira You could try merging master, where we just updated the pytype version used. Maybe that will help.

[rchen152]

Oh, I think pytype only recognizes paramspecs in Callables right now. So the Generic[_P] is probably what's tripping it up. Let me see if I can fix that.

[rchen152]

I just released a pytype version (2021.11.2) that should fix the pytype_test failure.

[srittau]

@Tomaz-Vieira could you update the pytype version in the requirements file?

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

isort (https://github.com/pycqa/isort.git)
+ isort/place.py:17: error: Returning Any from function declared to return "str"

pydantic (https://github.com/samuelcolvin/pydantic.git)
+ pydantic/tools.py:34: error: unused "type: ignore" comment

pandas (https://github.com/pandas-dev/pandas.git)
+ pandas/core/dtypes/cast.py:498: error: unused "type: ignore" comment

aiohttp (https://github.com/aio-libs/aiohttp.git)
+ aiohttp/multipart.py:516: error: Returning Any from function declared to return "str"  [no-any-return]
+ aiohttp/multipart.py:690: error: Returning Any from function declared to return "str"  [no-any-return]
+ aiohttp/connector.py:918: error: Returning Any from function declared to return "Optional[SSLContext]"  [no-any-return]
+ aiohttp/connector.py:924: error: Returning Any from function declared to return "Optional[SSLContext]"  [no-any-return]
+ aiohttp/connector.py:925: error: Returning Any from function declared to return "Optional[SSLContext]"  [no-any-return]
+ aiohttp/client_reqrep.py:1010: error: Returning Any from function declared to return "str"  [no-any-return]

pytest (https://github.com/pytest-dev/pytest.git)
- src/_pytest/config/__init__.py:1683: error: Argument 1 to "filterwarnings" has incompatible type "*Tuple[str, str, Type[Warning], str, int]"; expected "Union[Literal['default'], Literal['error'], Literal['ignore'], Literal['always'], Literal['module'], Literal['once']]"  [arg-type]
- src/_pytest/config/__init__.py:1686: error: Argument 1 to "filterwarnings" has incompatible type "*Tuple[str, str, Type[Warning], str, int]"; expected "Union[Literal['default'], Literal['error'], Literal['ignore'], Literal['always'], Literal['module'], Literal['once']]"  [arg-type]
+ src/_pytest/python.py:946: error: Unexpected keyword argument "indices" for "CallSpec2"  [call-arg]

edgedb (https://github.com/edgedb/edgedb.git)
+ edb/schema/objects.py:997: error: unused "type: ignore" comment
+ edb/schema/objects.py:1992:9: error: Returning Any from function declared to return "QualName"
+ edb/schema/objects.py:2223: error: unused "type: ignore" comment
+ edb/schema/objects.py:2637:9: error: Returning Any from function declared to return "Name"
+ edb/schema/schema.py:1146:9: error: Returning Any from function declared to return "FrozenSet[Cast]"
+ edb/schema/schema.py:1156:9: error: Returning Any from function declared to return "FrozenSet[Cast]"
+ edb/schema/schema.py:1166:9: error: Returning Any from function declared to return "FrozenSet[so.Object_T]"
+ edb/schema/schema.py:1412:9: error: Returning Any from function declared to return "Optional[Migration]"
+ edb/schema/scalars.py:132:9: error: Returning Any from function declared to return "bool"
+ edb/schema/scalars.py:163:9: error: Returning Any from function declared to return "bool"
+ edb/schema/scalars.py:176:9: error: Returning Any from function declared to return "int"
+ edb/schema/casts.py:91:5: error: Returning Any from function declared to return "bool"
+ edb/schema/casts.py:119:21: error: Returning Any from function declared to return "Optional[Type]"