Give PyCharm some help with @cache_in_self (#15238)

* Give PyCharm some help with `@cache_in_self`

* Changelog

* Fix import for old python versions
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David Robertson 2023-03-09 19:12:09 +00:00 committed by GitHub
parent caf43c3d7c
commit ce54477f6f
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2 changed files with 27 additions and 3 deletions

1
changelog.d/15238.misc Normal file
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@ -0,0 +1 @@
Improve type hints.

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@ -23,6 +23,8 @@ import functools
import logging
from typing import TYPE_CHECKING, Callable, Dict, List, Optional, TypeVar, cast
from typing_extensions import TypeAlias
from twisted.internet.interfaces import IOpenSSLContextFactory
from twisted.internet.tcp import Port
from twisted.web.iweb import IPolicyForHTTPS
@ -142,10 +144,31 @@ if TYPE_CHECKING:
from synapse.handlers.saml import SamlHandler
T = TypeVar("T")
# The annotation for `cache_in_self` used to be
# def (builder: Callable[["HomeServer"],T]) -> Callable[["HomeServer"],T]
# which mypy was happy with.
#
# But PyCharm was confused by this. If `foo` was decorated by `@cache_in_self`, then
# an expression like `hs.foo()`
#
# - would erroneously warn that we hadn't provided a `hs` argument to foo (PyCharm
# confused about boundmethods and unbound methods?), and
# - would be considered to have type `Any`, making for a poor autocomplete and
# cross-referencing experience.
#
# Instead, use a typevar `F` to express that `@cache_in_self` returns exactly the
# same type it receives. This isn't strictly true [*], but it's more than good
# enough to keep PyCharm and mypy happy.
#
# [*]: (e.g. `builder` could be an object with a __call__ attribute rather than a
# types.FunctionType instance, whereas the return value is always a
# types.FunctionType instance.)
T: TypeAlias = object
F = TypeVar("F", bound=Callable[["HomeServer"], T])
def cache_in_self(builder: Callable[["HomeServer"], T]) -> Callable[["HomeServer"], T]:
def cache_in_self(builder: F) -> F:
"""Wraps a function called e.g. `get_foo`, checking if `self.foo` exists and
returning if so. If not, calls the given function and sets `self.foo` to it.
@ -183,7 +206,7 @@ def cache_in_self(builder: Callable[["HomeServer"], T]) -> Callable[["HomeServer
return dep
return _get
return cast(F, _get)
class HomeServer(metaclass=abc.ABCMeta):