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mypy plugin to check @cached return types (#14911)

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Co-authored-by: David Robertson <davidr@element.io>
Co-authored-by: Patrick Cloke <patrickc@matrix.org>
Co-authored-by: Erik Johnston <erik@matrix.org>

Assert that the return type of callables wrapped in @cached
and @cachedList are cachable (aka immutable).
This commit is contained in:
David Robertson 2023-10-02 15:22:36 +01:00 committed by GitHub
parent 5725712d47
commit 1026776380
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8 changed files with 323 additions and 58 deletions
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1
changelog.d/14911.misc Normal file
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@ -0,0 +1 @@
Improve type hints.

287
scripts-dev/mypy_synapse_plugin.py
View file

@ -16,13 +16,24 @@
can crop up, e.g the cache descriptors.
"""
from typing import Callable, Optional, Type
from typing import Callable, Optional, Tuple, Type, Union
import mypy.types
from mypy.erasetype import remove_instance_last_known_values
from mypy.nodes import ARG_NAMED_OPT
from mypy.plugin import MethodSigContext, Plugin
from mypy.errorcodes import ErrorCode
from mypy.nodes import ARG_NAMED_OPT, TempNode, Var
from mypy.plugin import FunctionSigContext, MethodSigContext, Plugin
from mypy.typeops import bind_self
from mypy.types import CallableType, Instance, NoneType, UnionType
from mypy.types import (
AnyType,
CallableType,
Instance,
NoneType,
TupleType,
TypeAliasType,
UninhabitedType,
UnionType,
)
class SynapsePlugin(Plugin):
@ -36,9 +47,37 @@ class SynapsePlugin(Plugin):
)
):
return cached_function_method_signature
if fullname in (
"synapse.util.caches.descriptors._CachedFunctionDescriptor.__call__",
"synapse.util.caches.descriptors._CachedListFunctionDescriptor.__call__",
):
return check_is_cacheable_wrapper
return None
def _get_true_return_type(signature: CallableType) -> mypy.types.Type:
"""
Get the "final" return type of a callable which might return an Awaitable/Deferred.
"""
if isinstance(signature.ret_type, Instance):
# If a coroutine, unwrap the coroutine's return type.
if signature.ret_type.type.fullname == "typing.Coroutine":
return signature.ret_type.args[2]
# If an awaitable, unwrap the awaitable's final value.
elif signature.ret_type.type.fullname == "typing.Awaitable":
return signature.ret_type.args[0]
# If a Deferred, unwrap the Deferred's final value.
elif signature.ret_type.type.fullname == "twisted.internet.defer.Deferred":
return signature.ret_type.args[0]
# Otherwise, return the raw value of the function.
return signature.ret_type
def cached_function_method_signature(ctx: MethodSigContext) -> CallableType:
"""Fixes the `CachedFunction.__call__` signature to be correct.
@ -47,16 +86,17 @@ def cached_function_method_signature(ctx: MethodSigContext) -> CallableType:
1. the `self` argument needs to be marked as "bound";
2. any `cache_context` argument should be removed;
3. an optional keyword argument `on_invalidated` should be added.
4. Wrap the return type to always be a Deferred.
"""
# First we mark this as a bound function signature.
signature = bind_self(ctx.default_signature)
# 1. Mark this as a bound function signature.
signature: CallableType = bind_self(ctx.default_signature)
# Secondly, we remove any "cache_context" args.
# 2. Remove any "cache_context" args.
#
# Note: We should be only doing this if `cache_context=True` is set, but if
# it isn't then the code will raise an exception when its called anyway, so
# its not the end of the world.
# it's not the end of the world.
context_arg_index = None
for idx, name in enumerate(signature.arg_names):
if name == "cache_context":
@ -72,7 +112,7 @@ def cached_function_method_signature(ctx: MethodSigContext) -> CallableType:
arg_names.pop(context_arg_index)
arg_kinds.pop(context_arg_index)
# Third, we add an optional "on_invalidate" argument.
# 3. Add an optional "on_invalidate" argument.
#
# This is a either
# - a callable which accepts no input and returns nothing, or
@ -94,35 +134,16 @@ def cached_function_method_signature(ctx: MethodSigContext) -> CallableType:
arg_names.append("on_invalidate")
arg_kinds.append(ARG_NAMED_OPT) # Arg is an optional kwarg.
# Finally we ensure the return type is a Deferred.
if (
isinstance(signature.ret_type, Instance)
and signature.ret_type.type.fullname == "twisted.internet.defer.Deferred"
):
# If it is already a Deferred, nothing to do.
ret_type = signature.ret_type
else:
ret_arg = None
if isinstance(signature.ret_type, Instance):
# If a coroutine, wrap the coroutine's return type in a Deferred.
if signature.ret_type.type.fullname == "typing.Coroutine":
ret_arg = signature.ret_type.args[2]
# 4. Ensure the return type is a Deferred.
ret_arg = _get_true_return_type(signature)
# If an awaitable, wrap the awaitable's final value in a Deferred.
elif signature.ret_type.type.fullname == "typing.Awaitable":
ret_arg = signature.ret_type.args[0]
# Otherwise, wrap the return value in a Deferred.
if ret_arg is None:
ret_arg = signature.ret_type
# This should be able to use ctx.api.named_generic_type, but that doesn't seem
# to find the correct symbol for anything more than 1 module deep.
#
# modules is not part of CheckerPluginInterface. The following is a combination
# of TypeChecker.named_generic_type and TypeChecker.lookup_typeinfo.
sym = ctx.api.modules["twisted.internet.defer"].names.get("Deferred") # type: ignore[attr-defined]
ret_type = Instance(sym.node, [remove_instance_last_known_values(ret_arg)])
# This should be able to use ctx.api.named_generic_type, but that doesn't seem
# to find the correct symbol for anything more than 1 module deep.
#
# modules is not part of CheckerPluginInterface. The following is a combination
# of TypeChecker.named_generic_type and TypeChecker.lookup_typeinfo.
sym = ctx.api.modules["twisted.internet.defer"].names.get("Deferred") # type: ignore[attr-defined]
ret_type = Instance(sym.node, [remove_instance_last_known_values(ret_arg)])
signature = signature.copy_modified(
arg_types=arg_types,
@ -134,6 +155,198 @@ def cached_function_method_signature(ctx: MethodSigContext) -> CallableType:
return signature
def check_is_cacheable_wrapper(ctx: MethodSigContext) -> CallableType:
"""Asserts that the signature of a method returns a value which can be cached.
Makes no changes to the provided method signature.
"""
# The true signature, this isn't being modified so this is what will be returned.
signature: CallableType = ctx.default_signature
if not isinstance(ctx.args[0][0], TempNode):
ctx.api.note("Cached function is not a TempNode?!", ctx.context) # type: ignore[attr-defined]
return signature
orig_sig = ctx.args[0][0].type
if not isinstance(orig_sig, CallableType):
ctx.api.fail("Cached 'function' is not a callable", ctx.context)
return signature
check_is_cacheable(orig_sig, ctx)
return signature
def check_is_cacheable(
signature: CallableType,
ctx: Union[MethodSigContext, FunctionSigContext],
) -> None:
"""
Check if a callable returns a type which can be cached.
Args:
signature: The callable to check.
ctx: The signature context, used for error reporting.
"""
# Unwrap the true return type from the cached function.
return_type = _get_true_return_type(signature)
verbose = ctx.api.options.verbosity >= 1
# TODO Technically a cachedList only needs immutable values, but forcing them
# to return Mapping instead of Dict is fine.
ok, note = is_cacheable(return_type, signature, verbose)
if ok:
message = f"function {signature.name} is @cached, returning {return_type}"
else:
message = f"function {signature.name} is @cached, but has mutable return value {return_type}"
if note:
message += f" ({note})"
message = message.replace("builtins.", "").replace("typing.", "")
if ok and note:
ctx.api.note(message, ctx.context) # type: ignore[attr-defined]
elif not ok:
ctx.api.fail(message, ctx.context, code=AT_CACHED_MUTABLE_RETURN)
# Immutable simple values.
IMMUTABLE_VALUE_TYPES = {
"builtins.bool",
"builtins.int",
"builtins.float",
"builtins.str",
"builtins.bytes",
}
# Types defined in Synapse which are known to be immutable.
IMMUTABLE_CUSTOM_TYPES = {
"synapse.synapse_rust.acl.ServerAclEvaluator",
"synapse.synapse_rust.push.FilteredPushRules",
# This is technically not immutable, but close enough.
"signedjson.types.VerifyKey",
}
# Immutable containers only if the values are also immutable.
IMMUTABLE_CONTAINER_TYPES_REQUIRING_IMMUTABLE_ELEMENTS = {
"builtins.frozenset",
"builtins.tuple",
"typing.AbstractSet",
"typing.Sequence",
"immutabledict.immutabledict",
}
MUTABLE_CONTAINER_TYPES = {
"builtins.set",
"builtins.list",
"builtins.dict",
}
AT_CACHED_MUTABLE_RETURN = ErrorCode(
"synapse-@cached-mutable",
"@cached() should have an immutable return type",
"General",
)
def is_cacheable(
rt: mypy.types.Type, signature: CallableType, verbose: bool
) -> Tuple[bool, Optional[str]]:
"""
Check if a particular type is cachable.
A type is cachable if it is immutable; for complex types this recurses to
check each type parameter.
Returns: a 2-tuple (cacheable, message).
- cachable: False means the type is definitely not cacheable;
true means anything else.
- Optional message.
"""
# This should probably be done via a TypeVisitor. Apologies to the reader!
if isinstance(rt, AnyType):
return True, ("may be mutable" if verbose else None)
elif isinstance(rt, Instance):
if (
rt.type.fullname in IMMUTABLE_VALUE_TYPES
or rt.type.fullname in IMMUTABLE_CUSTOM_TYPES
):
# "Simple" types are generally immutable.
return True, None
elif rt.type.fullname == "typing.Mapping":
# Generally mapping keys are immutable, but they only *have* to be
# hashable, which doesn't imply immutability. E.g. Mapping[K, V]
# is cachable iff K and V are cachable.
return is_cacheable(rt.args[0], signature, verbose) and is_cacheable(
rt.args[1], signature, verbose
)
elif rt.type.fullname in IMMUTABLE_CONTAINER_TYPES_REQUIRING_IMMUTABLE_ELEMENTS:
# E.g. Collection[T] is cachable iff T is cachable.
return is_cacheable(rt.args[0], signature, verbose)
elif rt.type.fullname in MUTABLE_CONTAINER_TYPES:
# Mutable containers are mutable regardless of their underlying type.
return False, None
elif "attrs" in rt.type.metadata:
# attrs classes are only cachable iff it is frozen (immutable itself)
# and all attributes are cachable.
frozen = rt.type.metadata["attrs"]["frozen"]
if frozen:
for attribute in rt.type.metadata["attrs"]["attributes"]:
attribute_name = attribute["name"]
symbol_node = rt.type.names[attribute_name].node
assert isinstance(symbol_node, Var)
assert symbol_node.type is not None
ok, note = is_cacheable(symbol_node.type, signature, verbose)
if not ok:
return False, f"non-frozen attrs property: {attribute_name}"
# All attributes were frozen.
return True, None
else:
return False, "non-frozen attrs class"
else:
# Ensure we fail for unknown types, these generally means that the
# above code is not complete.
return (
False,
f"Don't know how to handle {rt.type.fullname} return type instance",
)
elif isinstance(rt, NoneType):
# None is cachable.
return True, None
elif isinstance(rt, (TupleType, UnionType)):
# Tuples and unions are cachable iff all their items are cachable.
for item in rt.items:
ok, note = is_cacheable(item, signature, verbose)
if not ok:
return False, note
# This discards notes but that's probably fine
return True, None
elif isinstance(rt, TypeAliasType):
# For a type alias, check if the underlying real type is cachable.
return is_cacheable(mypy.types.get_proper_type(rt), signature, verbose)
elif isinstance(rt, UninhabitedType) and rt.is_noreturn:
# There is no return value, just consider it cachable. This is only used
# in tests.
return True, None
else:
# Ensure we fail for unknown types, these generally means that the
# above code is not complete.
return False, f"Don't know how to handle {type(rt).__qualname__} return type"
def plugin(version: str) -> Type[SynapsePlugin]:
# This is the entry point of the plugin, and lets us deal with the fact
# that the mypy plugin interface is *not* stable by looking at the version

4
synapse/handlers/room_list.py
View file

@ -33,7 +33,7 @@ from synapse.api.errors import (
RequestSendFailed,
SynapseError,
)
from synapse.types import JsonDict, ThirdPartyInstanceID
from synapse.types import JsonDict, JsonMapping, ThirdPartyInstanceID
from synapse.util.caches.descriptors import _CacheContext, cached
from synapse.util.caches.response_cache import ResponseCache
@ -256,7 +256,7 @@ class RoomListHandler:
cache_context: _CacheContext,
with_alias: bool = True,
allow_private: bool = False,
) -> Optional[JsonDict]:
) -> Optional[JsonMapping]:
"""Returns the entry for a room
Args:

7
synapse/storage/databases/main/event_push_actions.py
View file

@ -182,6 +182,7 @@ class UserPushAction(EmailPushAction):
profile_tag: str
# TODO This is used as a cached value and is mutable.
@attr.s(slots=True, auto_attribs=True)
class NotifCounts:
"""
@ -193,7 +194,7 @@ class NotifCounts:
highlight_count: int = 0
@attr.s(slots=True, auto_attribs=True)
@attr.s(slots=True, frozen=True, auto_attribs=True)
class RoomNotifCounts:
"""
The per-user, per-room count of notifications. Used by sync and push.
@ -201,7 +202,7 @@ class RoomNotifCounts:
main_timeline: NotifCounts
# Map of thread ID to the notification counts.
threads: Dict[str, NotifCounts]
threads: Mapping[str, NotifCounts]
@staticmethod
def empty() -> "RoomNotifCounts":
@ -483,7 +484,7 @@ class EventPushActionsWorkerStore(ReceiptsWorkerStore, StreamWorkerStore, SQLBas
return room_to_count
@cached(tree=True, max_entries=5000, iterable=True)
@cached(tree=True, max_entries=5000, iterable=True) # type: ignore[synapse-@cached-mutable]
async def get_unread_event_push_actions_by_room_for_user(
self,
room_id: str,

12
synapse/storage/databases/main/relations.py
View file

@ -458,7 +458,7 @@ class RelationsWorkerStore(SQLBaseStore):
)
return result is not None
@cached()
@cached() # type: ignore[synapse-@cached-mutable]
async def get_references_for_event(self, event_id: str) -> List[JsonDict]:
raise NotImplementedError()
@ -512,11 +512,12 @@ class RelationsWorkerStore(SQLBaseStore):
"_get_references_for_events_txn", _get_references_for_events_txn
)
@cached()
@cached() # type: ignore[synapse-@cached-mutable]
def get_applicable_edit(self, event_id: str) -> Optional[EventBase]:
raise NotImplementedError()
@cachedList(cached_method_name="get_applicable_edit", list_name="event_ids")
# TODO: This returns a mutable object, which is generally bad.
@cachedList(cached_method_name="get_applicable_edit", list_name="event_ids") # type: ignore[synapse-@cached-mutable]
async def get_applicable_edits(
self, event_ids: Collection[str]
) -> Mapping[str, Optional[EventBase]]:
@ -598,11 +599,12 @@ class RelationsWorkerStore(SQLBaseStore):
for original_event_id in event_ids
}
@cached()
@cached() # type: ignore[synapse-@cached-mutable]
def get_thread_summary(self, event_id: str) -> Optional[Tuple[int, EventBase]]:
raise NotImplementedError()
@cachedList(cached_method_name="get_thread_summary", list_name="event_ids")
# TODO: This returns a mutable object, which is generally bad.
@cachedList(cached_method_name="get_thread_summary", list_name="event_ids") # type: ignore[synapse-@cached-mutable]
async def get_thread_summaries(
self, event_ids: Collection[str]
) -> Mapping[str, Optional[Tuple[int, EventBase]]]:

5
synapse/storage/databases/main/roommember.py
View file

@ -275,7 +275,7 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):
_get_users_in_room_with_profiles,
)
@cached(max_entries=100000)
@cached(max_entries=100000) # type: ignore[synapse-@cached-mutable]
async def get_room_summary(self, room_id: str) -> Mapping[str, MemberSummary]:
"""Get the details of a room roughly suitable for use by the room
summary extension to /sync. Useful when lazy loading room members.
@ -1071,7 +1071,8 @@ class RoomMemberWorkerStore(EventsWorkerStore, CacheInvalidationWorkerStore):
)
return {row["event_id"]: row["membership"] for row in rows}
@cached(max_entries=10000)
# TODO This returns a mutable object, which is generally confusing when using a cache.
@cached(max_entries=10000) # type: ignore[synapse-@cached-mutable]
def _get_joined_hosts_cache(self, room_id: str) -> "_JoinedHostsCache":
return _JoinedHostsCache()

1
synapse/storage/roommember.py
View file

@ -45,6 +45,7 @@ class ProfileInfo:
display_name: Optional[str]
# TODO This is used as a cached value and is mutable.
@attr.s(slots=True, frozen=True, weakref_slot=False, auto_attribs=True)
class MemberSummary:
# A truncated list of (user_id, event_id) tuples for users of a given

64
synapse/util/caches/descriptors.py
View file

@ -36,6 +36,8 @@ from typing import (
)
from weakref import WeakValueDictionary
import attr
from twisted.internet import defer
from twisted.python.failure import Failure
@ -466,6 +468,35 @@ class _CacheContext:
)
@attr.s(auto_attribs=True, slots=True, frozen=True)
class _CachedFunctionDescriptor:
"""Helper for `@cached`, we name it so that we can hook into it with mypy
plugin."""
max_entries: int
num_args: Optional[int]
uncached_args: Optional[Collection[str]]
tree: bool
cache_context: bool
iterable: bool
prune_unread_entries: bool
name: Optional[str]
def __call__(self, orig: F) -> CachedFunction[F]:
d = DeferredCacheDescriptor(
orig,
max_entries=self.max_entries,
num_args=self.num_args,
uncached_args=self.uncached_args,
tree=self.tree,
cache_context=self.cache_context,
iterable=self.iterable,
prune_unread_entries=self.prune_unread_entries,
name=self.name,
)
return cast(CachedFunction[F], d)
def cached(
*,
max_entries: int = 1000,
@ -476,9 +507,8 @@ def cached(
iterable: bool = False,
prune_unread_entries: bool = True,
name: Optional[str] = None,
) -> Callable[[F], CachedFunction[F]]:
func = lambda orig: DeferredCacheDescriptor(
orig,
) -> _CachedFunctionDescriptor:
return _CachedFunctionDescriptor(
max_entries=max_entries,
num_args=num_args,
uncached_args=uncached_args,
@ -489,7 +519,26 @@ def cached(
name=name,
)
return cast(Callable[[F], CachedFunction[F]], func)
@attr.s(auto_attribs=True, slots=True, frozen=True)
class _CachedListFunctionDescriptor:
"""Helper for `@cachedList`, we name it so that we can hook into it with mypy
plugin."""
cached_method_name: str
list_name: str
num_args: Optional[int] = None
name: Optional[str] = None
def __call__(self, orig: F) -> CachedFunction[F]:
d = DeferredCacheListDescriptor(
orig,
cached_method_name=self.cached_method_name,
list_name=self.list_name,
num_args=self.num_args,
name=self.name,
)
return cast(CachedFunction[F], d)
def cachedList(
@ -498,7 +547,7 @@ def cachedList(
list_name: str,
num_args: Optional[int] = None,
name: Optional[str] = None,
) -> Callable[[F], CachedFunction[F]]:
) -> _CachedListFunctionDescriptor:
"""Creates a descriptor that wraps a function in a `DeferredCacheListDescriptor`.
Used to do batch lookups for an already created cache. One of the arguments
@ -527,16 +576,13 @@ def cachedList(
def batch_do_something(self, first_arg, second_args):
...
"""
func = lambda orig: DeferredCacheListDescriptor(
orig,
return _CachedListFunctionDescriptor(
cached_method_name=cached_method_name,
list_name=list_name,
num_args=num_args,
name=name,
)
return cast(Callable[[F], CachedFunction[F]], func)
def _get_cache_key_builder(
param_names: Sequence[str],