mirror of
https://github.com/element-hq/synapse.git
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1026776380
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).
357 lines
12 KiB
Python
357 lines
12 KiB
Python
# Copyright 2020 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""This is a mypy plugin for Synpase to deal with some of the funky typing that
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can crop up, e.g the cache descriptors.
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"""
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from typing import Callable, Optional, Tuple, Type, Union
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import mypy.types
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from mypy.erasetype import remove_instance_last_known_values
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from mypy.errorcodes import ErrorCode
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from mypy.nodes import ARG_NAMED_OPT, TempNode, Var
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from mypy.plugin import FunctionSigContext, MethodSigContext, Plugin
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from mypy.typeops import bind_self
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from mypy.types import (
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AnyType,
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CallableType,
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Instance,
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NoneType,
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TupleType,
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TypeAliasType,
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UninhabitedType,
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UnionType,
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)
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class SynapsePlugin(Plugin):
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def get_method_signature_hook(
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self, fullname: str
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) -> Optional[Callable[[MethodSigContext], CallableType]]:
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if fullname.startswith(
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(
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"synapse.util.caches.descriptors.CachedFunction.__call__",
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"synapse.util.caches.descriptors._LruCachedFunction.__call__",
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)
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):
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return cached_function_method_signature
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if fullname in (
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"synapse.util.caches.descriptors._CachedFunctionDescriptor.__call__",
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"synapse.util.caches.descriptors._CachedListFunctionDescriptor.__call__",
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):
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return check_is_cacheable_wrapper
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return None
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def _get_true_return_type(signature: CallableType) -> mypy.types.Type:
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"""
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Get the "final" return type of a callable which might return an Awaitable/Deferred.
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"""
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if isinstance(signature.ret_type, Instance):
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# If a coroutine, unwrap the coroutine's return type.
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if signature.ret_type.type.fullname == "typing.Coroutine":
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return signature.ret_type.args[2]
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# If an awaitable, unwrap the awaitable's final value.
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elif signature.ret_type.type.fullname == "typing.Awaitable":
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return signature.ret_type.args[0]
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# If a Deferred, unwrap the Deferred's final value.
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elif signature.ret_type.type.fullname == "twisted.internet.defer.Deferred":
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return signature.ret_type.args[0]
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# Otherwise, return the raw value of the function.
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return signature.ret_type
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def cached_function_method_signature(ctx: MethodSigContext) -> CallableType:
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"""Fixes the `CachedFunction.__call__` signature to be correct.
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It already has *almost* the correct signature, except:
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1. the `self` argument needs to be marked as "bound";
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2. any `cache_context` argument should be removed;
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3. an optional keyword argument `on_invalidated` should be added.
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4. Wrap the return type to always be a Deferred.
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"""
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# 1. Mark this as a bound function signature.
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signature: CallableType = bind_self(ctx.default_signature)
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# 2. Remove any "cache_context" args.
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#
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# Note: We should be only doing this if `cache_context=True` is set, but if
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# it isn't then the code will raise an exception when its called anyway, so
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# it's not the end of the world.
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context_arg_index = None
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for idx, name in enumerate(signature.arg_names):
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if name == "cache_context":
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context_arg_index = idx
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break
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arg_types = list(signature.arg_types)
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arg_names = list(signature.arg_names)
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arg_kinds = list(signature.arg_kinds)
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if context_arg_index:
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arg_types.pop(context_arg_index)
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arg_names.pop(context_arg_index)
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arg_kinds.pop(context_arg_index)
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# 3. Add an optional "on_invalidate" argument.
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#
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# This is a either
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# - a callable which accepts no input and returns nothing, or
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# - None.
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calltyp = UnionType(
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[
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NoneType(),
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CallableType(
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arg_types=[],
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arg_kinds=[],
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arg_names=[],
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ret_type=NoneType(),
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fallback=ctx.api.named_generic_type("builtins.function", []),
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),
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]
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)
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arg_types.append(calltyp)
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arg_names.append("on_invalidate")
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arg_kinds.append(ARG_NAMED_OPT) # Arg is an optional kwarg.
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# 4. Ensure the return type is a Deferred.
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ret_arg = _get_true_return_type(signature)
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# This should be able to use ctx.api.named_generic_type, but that doesn't seem
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# to find the correct symbol for anything more than 1 module deep.
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#
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# modules is not part of CheckerPluginInterface. The following is a combination
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# of TypeChecker.named_generic_type and TypeChecker.lookup_typeinfo.
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sym = ctx.api.modules["twisted.internet.defer"].names.get("Deferred") # type: ignore[attr-defined]
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ret_type = Instance(sym.node, [remove_instance_last_known_values(ret_arg)])
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signature = signature.copy_modified(
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arg_types=arg_types,
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arg_names=arg_names,
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arg_kinds=arg_kinds,
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ret_type=ret_type,
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)
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return signature
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def check_is_cacheable_wrapper(ctx: MethodSigContext) -> CallableType:
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"""Asserts that the signature of a method returns a value which can be cached.
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Makes no changes to the provided method signature.
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"""
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# The true signature, this isn't being modified so this is what will be returned.
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signature: CallableType = ctx.default_signature
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if not isinstance(ctx.args[0][0], TempNode):
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ctx.api.note("Cached function is not a TempNode?!", ctx.context) # type: ignore[attr-defined]
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return signature
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orig_sig = ctx.args[0][0].type
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if not isinstance(orig_sig, CallableType):
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ctx.api.fail("Cached 'function' is not a callable", ctx.context)
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return signature
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check_is_cacheable(orig_sig, ctx)
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return signature
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def check_is_cacheable(
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signature: CallableType,
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ctx: Union[MethodSigContext, FunctionSigContext],
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) -> None:
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"""
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Check if a callable returns a type which can be cached.
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Args:
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signature: The callable to check.
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ctx: The signature context, used for error reporting.
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"""
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# Unwrap the true return type from the cached function.
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return_type = _get_true_return_type(signature)
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verbose = ctx.api.options.verbosity >= 1
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# TODO Technically a cachedList only needs immutable values, but forcing them
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# to return Mapping instead of Dict is fine.
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ok, note = is_cacheable(return_type, signature, verbose)
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if ok:
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message = f"function {signature.name} is @cached, returning {return_type}"
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else:
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message = f"function {signature.name} is @cached, but has mutable return value {return_type}"
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if note:
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message += f" ({note})"
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message = message.replace("builtins.", "").replace("typing.", "")
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if ok and note:
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ctx.api.note(message, ctx.context) # type: ignore[attr-defined]
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elif not ok:
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ctx.api.fail(message, ctx.context, code=AT_CACHED_MUTABLE_RETURN)
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# Immutable simple values.
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IMMUTABLE_VALUE_TYPES = {
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"builtins.bool",
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"builtins.int",
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"builtins.float",
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"builtins.str",
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"builtins.bytes",
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}
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# Types defined in Synapse which are known to be immutable.
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IMMUTABLE_CUSTOM_TYPES = {
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"synapse.synapse_rust.acl.ServerAclEvaluator",
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"synapse.synapse_rust.push.FilteredPushRules",
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# This is technically not immutable, but close enough.
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"signedjson.types.VerifyKey",
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}
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# Immutable containers only if the values are also immutable.
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IMMUTABLE_CONTAINER_TYPES_REQUIRING_IMMUTABLE_ELEMENTS = {
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"builtins.frozenset",
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"builtins.tuple",
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"typing.AbstractSet",
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"typing.Sequence",
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"immutabledict.immutabledict",
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}
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MUTABLE_CONTAINER_TYPES = {
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"builtins.set",
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"builtins.list",
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"builtins.dict",
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}
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AT_CACHED_MUTABLE_RETURN = ErrorCode(
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"synapse-@cached-mutable",
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"@cached() should have an immutable return type",
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"General",
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)
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def is_cacheable(
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rt: mypy.types.Type, signature: CallableType, verbose: bool
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) -> Tuple[bool, Optional[str]]:
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"""
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Check if a particular type is cachable.
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A type is cachable if it is immutable; for complex types this recurses to
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check each type parameter.
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Returns: a 2-tuple (cacheable, message).
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- cachable: False means the type is definitely not cacheable;
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true means anything else.
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- Optional message.
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"""
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# This should probably be done via a TypeVisitor. Apologies to the reader!
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if isinstance(rt, AnyType):
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return True, ("may be mutable" if verbose else None)
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elif isinstance(rt, Instance):
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if (
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rt.type.fullname in IMMUTABLE_VALUE_TYPES
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or rt.type.fullname in IMMUTABLE_CUSTOM_TYPES
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):
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# "Simple" types are generally immutable.
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return True, None
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elif rt.type.fullname == "typing.Mapping":
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# Generally mapping keys are immutable, but they only *have* to be
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# hashable, which doesn't imply immutability. E.g. Mapping[K, V]
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# is cachable iff K and V are cachable.
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return is_cacheable(rt.args[0], signature, verbose) and is_cacheable(
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rt.args[1], signature, verbose
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)
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elif rt.type.fullname in IMMUTABLE_CONTAINER_TYPES_REQUIRING_IMMUTABLE_ELEMENTS:
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# E.g. Collection[T] is cachable iff T is cachable.
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return is_cacheable(rt.args[0], signature, verbose)
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elif rt.type.fullname in MUTABLE_CONTAINER_TYPES:
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# Mutable containers are mutable regardless of their underlying type.
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return False, None
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elif "attrs" in rt.type.metadata:
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# attrs classes are only cachable iff it is frozen (immutable itself)
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# and all attributes are cachable.
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frozen = rt.type.metadata["attrs"]["frozen"]
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if frozen:
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for attribute in rt.type.metadata["attrs"]["attributes"]:
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attribute_name = attribute["name"]
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symbol_node = rt.type.names[attribute_name].node
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assert isinstance(symbol_node, Var)
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assert symbol_node.type is not None
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ok, note = is_cacheable(symbol_node.type, signature, verbose)
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if not ok:
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return False, f"non-frozen attrs property: {attribute_name}"
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# All attributes were frozen.
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return True, None
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else:
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return False, "non-frozen attrs class"
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else:
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# Ensure we fail for unknown types, these generally means that the
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# above code is not complete.
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return (
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False,
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f"Don't know how to handle {rt.type.fullname} return type instance",
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)
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elif isinstance(rt, NoneType):
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# None is cachable.
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return True, None
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elif isinstance(rt, (TupleType, UnionType)):
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# Tuples and unions are cachable iff all their items are cachable.
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for item in rt.items:
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ok, note = is_cacheable(item, signature, verbose)
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if not ok:
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return False, note
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# This discards notes but that's probably fine
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return True, None
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elif isinstance(rt, TypeAliasType):
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# For a type alias, check if the underlying real type is cachable.
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return is_cacheable(mypy.types.get_proper_type(rt), signature, verbose)
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elif isinstance(rt, UninhabitedType) and rt.is_noreturn:
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# There is no return value, just consider it cachable. This is only used
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# in tests.
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return True, None
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else:
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# Ensure we fail for unknown types, these generally means that the
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# above code is not complete.
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return False, f"Don't know how to handle {type(rt).__qualname__} return type"
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def plugin(version: str) -> Type[SynapsePlugin]:
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# This is the entry point of the plugin, and lets us deal with the fact
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# that the mypy plugin interface is *not* stable by looking at the version
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# string.
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#
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# However, since we pin the version of mypy Synapse uses in CI, we don't
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# really care.
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return SynapsePlugin
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