diff options
| -rw-r--r-- | changelog.d/15238.misc | 1 | ||||
| -rw-r--r-- | synapse/server.py | 29 |
2 files changed, 27 insertions, 3 deletions
diff --git a/changelog.d/15238.misc b/changelog.d/15238.misc new file mode 100644 index 0000000000..93ceaeafc9 --- /dev/null +++ b/changelog.d/15238.misc @@ -0,0 +1 @@ +Improve type hints. diff --git a/synapse/server.py b/synapse/server.py index df80fc1beb..8078463530 100644 --- a/synapse/server.py +++ b/synapse/server.py @@ -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): |