Additional type hints for config module. (#11465)

This adds some misc. type hints to helper methods used
in the `synapse.config` module.

15 files changed, 129 insertions, 99 deletions

diff --git a/changelog.d/11465.misc b/changelog.d/11465.misc
new file mode 100644
index 0000000000..aadc938b2b
--- /dev/null
+++ b/changelog.d/11465.misc
@@ -0,0 +1 @@
+Add missing type hints to `synapse.config` module.
diff --git a/synapse/app/_base.py b/synapse/app/_base.py
index 807ee3d46e..5fc59c1be1 100644
--- a/synapse/app/_base.py
+++ b/synapse/app/_base.py
@@ -32,6 +32,7 @@ from typing import (
     Iterable,
     List,
     NoReturn,
+    Optional,
     Tuple,
     cast,
 )
@@ -129,7 +130,7 @@ def start_worker_reactor(
 def start_reactor(
     appname: str,
     soft_file_limit: int,
-    gc_thresholds: Tuple[int, int, int],
+    gc_thresholds: Optional[Tuple[int, int, int]],
     pid_file: str,
     daemonize: bool,
     print_pidfile: bool,
diff --git a/synapse/config/__main__.py b/synapse/config/__main__.py
index c555f5f914..b2a7a89a35 100644
--- a/synapse/config/__main__.py
+++ b/synapse/config/__main__.py
@@ -13,12 +13,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import sys
+from typing import List
 
 from synapse.config._base import ConfigError
 from synapse.config.homeserver import HomeServerConfig
 
 
-def main(args):
+def main(args: List[str]) -> None:
     action = args[1] if len(args) > 1 and args[1] == "read" else None
     # If we're reading a key in the config file, then `args[1]` will be `read`  and `args[2]`
     # will be the key to read.
diff --git a/synapse/config/appservice.py b/synapse/config/appservice.py
index 1ebea88db2..e4bb7224a4 100644
--- a/synapse/config/appservice.py
+++ b/synapse/config/appservice.py
@@ -1,4 +1,5 @@
 # Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -13,14 +14,14 @@
 # limitations under the License.
 
 import logging
-from typing import Dict
+from typing import Dict, List
 from urllib import parse as urlparse
 
 import yaml
 from netaddr import IPSet
 
 from synapse.appservice import ApplicationService
-from synapse.types import UserID
+from synapse.types import JsonDict, UserID
 
 from ._base import Config, ConfigError
 
@@ -30,12 +31,12 @@ logger = logging.getLogger(__name__)
 class AppServiceConfig(Config):
     section = "appservice"
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         self.app_service_config_files = config.get("app_service_config_files", [])
         self.notify_appservices = config.get("notify_appservices", True)
         self.track_appservice_user_ips = config.get("track_appservice_user_ips", False)
 
-    def generate_config_section(cls, **kwargs):
+    def generate_config_section(cls, **kwargs) -> str:
         return """\
         # A list of application service config files to use
         #
@@ -50,7 +51,9 @@ class AppServiceConfig(Config):
         """
 
 
-def load_appservices(hostname, config_files):
+def load_appservices(
+    hostname: str, config_files: List[str]
+) -> List[ApplicationService]:
     """Returns a list of Application Services from the config files."""
     if not isinstance(config_files, list):
         logger.warning("Expected %s to be a list of AS config files.", config_files)
@@ -93,7 +96,9 @@ def load_appservices(hostname, config_files):
     return appservices
 
 
-def _load_appservice(hostname, as_info, config_filename):
+def _load_appservice(
+    hostname: str, as_info: JsonDict, config_filename: str
+) -> ApplicationService:
     required_string_fields = ["id", "as_token", "hs_token", "sender_localpart"]
     for field in required_string_fields:
         if not isinstance(as_info.get(field), str):
@@ -115,9 +120,9 @@ def _load_appservice(hostname, as_info, config_filename):
     user_id = user.to_string()
 
     # Rate limiting for users of this AS is on by default (excludes sender)
-    rate_limited = True
-    if isinstance(as_info.get("rate_limited"), bool):
-        rate_limited = as_info.get("rate_limited")
+    rate_limited = as_info.get("rate_limited")
+    if not isinstance(rate_limited, bool):
+        rate_limited = True
 
     # namespace checks
     if not isinstance(as_info.get("namespaces"), dict):
diff --git a/synapse/config/cache.py b/synapse/config/cache.py
index f054455534..d9d85f98e1 100644
--- a/synapse/config/cache.py
+++ b/synapse/config/cache.py
@@ -1,4 +1,4 @@
-# Copyright 2019 Matrix.org Foundation C.I.C.
+# Copyright 2019-2021 Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -17,6 +17,8 @@ import re
 import threading
 from typing import Callable, Dict, Optional
 
+import attr
+
 from synapse.python_dependencies import DependencyException, check_requirements
 
 from ._base import Config, ConfigError
@@ -34,13 +36,13 @@ _DEFAULT_FACTOR_SIZE = 0.5
 _DEFAULT_EVENT_CACHE_SIZE = "10K"
 
 
+@attr.s(slots=True, auto_attribs=True)
 class CacheProperties:
-    def __init__(self):
-        # The default factor size for all caches
-        self.default_factor_size = float(
-            os.environ.get(_CACHE_PREFIX, _DEFAULT_FACTOR_SIZE)
-        )
-        self.resize_all_caches_func = None
+    # The default factor size for all caches
+    default_factor_size: float = float(
+        os.environ.get(_CACHE_PREFIX, _DEFAULT_FACTOR_SIZE)
+    )
+    resize_all_caches_func: Optional[Callable[[], None]] = None
 
 
 properties = CacheProperties()
@@ -62,7 +64,7 @@ def _canonicalise_cache_name(cache_name: str) -> str:
 
 def add_resizable_cache(
     cache_name: str, cache_resize_callback: Callable[[float], None]
-):
+) -> None:
     """Register a cache that's size can dynamically change
 
     Args:
@@ -91,7 +93,7 @@ class CacheConfig(Config):
     _environ = os.environ
 
     @staticmethod
-    def reset():
+    def reset() -> None:
         """Resets the caches to their defaults. Used for tests."""
         properties.default_factor_size = float(
             os.environ.get(_CACHE_PREFIX, _DEFAULT_FACTOR_SIZE)
@@ -100,7 +102,7 @@ class CacheConfig(Config):
         with _CACHES_LOCK:
             _CACHES.clear()
 
-    def generate_config_section(self, **kwargs):
+    def generate_config_section(self, **kwargs) -> str:
         return """\
         ## Caching ##
 
@@ -162,7 +164,7 @@ class CacheConfig(Config):
           #sync_response_cache_duration: 2m
         """
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         self.event_cache_size = self.parse_size(
             config.get("event_cache_size", _DEFAULT_EVENT_CACHE_SIZE)
         )
@@ -232,7 +234,7 @@ class CacheConfig(Config):
         # needing an instance of Config
         properties.resize_all_caches_func = self.resize_all_caches
 
-    def resize_all_caches(self):
+    def resize_all_caches(self) -> None:
         """Ensure all cache sizes are up to date
 
         For each cache, run the mapped callback function with either
diff --git a/synapse/config/cas.py b/synapse/config/cas.py
index 3f81814043..6f2754092e 100644
--- a/synapse/config/cas.py
+++ b/synapse/config/cas.py
@@ -1,4 +1,5 @@
 # Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -28,7 +29,7 @@ class CasConfig(Config):
 
     section = "cas"
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         cas_config = config.get("cas_config", None)
         self.cas_enabled = cas_config and cas_config.get("enabled", True)
 
@@ -51,7 +52,7 @@ class CasConfig(Config):
             self.cas_displayname_attribute = None
             self.cas_required_attributes = []
 
-    def generate_config_section(self, config_dir_path, server_name, **kwargs):
+    def generate_config_section(self, config_dir_path, server_name, **kwargs) -> str:
         return """\
         # Enable Central Authentication Service (CAS) for registration and login.
         #
diff --git a/synapse/config/database.py b/synapse/config/database.py
index 651e31b576..06ccf15cd9 100644
--- a/synapse/config/database.py
+++ b/synapse/config/database.py
@@ -1,5 +1,5 @@
 # Copyright 2014-2016 OpenMarket Ltd
-# Copyright 2020 The Matrix.org Foundation C.I.C.
+# Copyright 2020-2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -12,6 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import argparse
 import logging
 import os
 
@@ -119,7 +120,7 @@ class DatabaseConfig(Config):
 
         self.databases = []
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         # We *experimentally* support specifying multiple databases via the
         # `databases` key. This is a map from a label to database config in the
         # same format as the `database` config option, plus an extra
@@ -163,12 +164,12 @@ class DatabaseConfig(Config):
             self.databases = [DatabaseConnectionConfig("master", database_config)]
             self.set_databasepath(database_path)
 
-    def generate_config_section(self, data_dir_path, **kwargs):
+    def generate_config_section(self, data_dir_path, **kwargs) -> str:
         return DEFAULT_CONFIG % {
             "database_path": os.path.join(data_dir_path, "homeserver.db")
         }
 
-    def read_arguments(self, args):
+    def read_arguments(self, args: argparse.Namespace) -> None:
         """
         Cases for the cli input:
           - If no databases are configured and no database_path is set, raise.
@@ -194,7 +195,7 @@ class DatabaseConfig(Config):
         else:
             logger.warning(NON_SQLITE_DATABASE_PATH_WARNING)
 
-    def set_databasepath(self, database_path):
+    def set_databasepath(self, database_path: str) -> None:
 
         if database_path != ":memory:":
             database_path = self.abspath(database_path)
@@ -202,7 +203,7 @@ class DatabaseConfig(Config):
         self.databases[0].config["args"]["database"] = database_path
 
     @staticmethod
-    def add_arguments(parser):
+    def add_arguments(parser: argparse.ArgumentParser) -> None:
         db_group = parser.add_argument_group("database")
         db_group.add_argument(
             "-d",
diff --git a/synapse/config/logger.py b/synapse/config/logger.py
index 63aab0babe..ea69b9bd9b 100644
--- a/synapse/config/logger.py
+++ b/synapse/config/logger.py
@@ -1,4 +1,5 @@
 # Copyright 2014-2016 OpenMarket Ltd
+# Copyright 2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -18,7 +19,7 @@ import os
 import sys
 import threading
 from string import Template
-from typing import TYPE_CHECKING, Any, Dict
+from typing import TYPE_CHECKING, Any, Dict, Optional
 
 import yaml
 from zope.interface import implementer
@@ -40,6 +41,7 @@ from synapse.util.versionstring import get_version_string
 from ._base import Config, ConfigError
 
 if TYPE_CHECKING:
+    from synapse.config.homeserver import HomeServerConfig
     from synapse.server import HomeServer
 
 DEFAULT_LOG_CONFIG = Template(
@@ -141,13 +143,13 @@ removed in Synapse 1.3.0. You should instead set up a separate log configuration
 class LoggingConfig(Config):
     section = "logging"
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         if config.get("log_file"):
             raise ConfigError(LOG_FILE_ERROR)
         self.log_config = self.abspath(config.get("log_config"))
         self.no_redirect_stdio = config.get("no_redirect_stdio", False)
 
-    def generate_config_section(self, config_dir_path, server_name, **kwargs):
+    def generate_config_section(self, config_dir_path, server_name, **kwargs) -> str:
         log_config = os.path.join(config_dir_path, server_name + ".log.config")
         return (
             """\
@@ -161,14 +163,14 @@ class LoggingConfig(Config):
             % locals()
         )
 
-    def read_arguments(self, args):
+    def read_arguments(self, args: argparse.Namespace) -> None:
         if args.no_redirect_stdio is not None:
             self.no_redirect_stdio = args.no_redirect_stdio
         if args.log_file is not None:
             raise ConfigError(LOG_FILE_ERROR)
 
     @staticmethod
-    def add_arguments(parser):
+    def add_arguments(parser: argparse.ArgumentParser) -> None:
         logging_group = parser.add_argument_group("logging")
         logging_group.add_argument(
             "-n",
@@ -197,7 +199,9 @@ class LoggingConfig(Config):
                 log_config_file.write(DEFAULT_LOG_CONFIG.substitute(log_file=log_file))
 
 
-def _setup_stdlib_logging(config, log_config_path, logBeginner: LogBeginner) -> None:
+def _setup_stdlib_logging(
+    config: "HomeServerConfig", log_config_path: Optional[str], logBeginner: LogBeginner
+) -> None:
     """
     Set up Python standard library logging.
     """
@@ -230,7 +234,7 @@ def _setup_stdlib_logging(config, log_config_path, logBeginner: LogBeginner) ->
     log_metadata_filter = MetadataFilter({"server_name": config.server.server_name})
     old_factory = logging.getLogRecordFactory()
 
-    def factory(*args, **kwargs):
+    def factory(*args: Any, **kwargs: Any) -> logging.LogRecord:
         record = old_factory(*args, **kwargs)
         log_context_filter.filter(record)
         log_metadata_filter.filter(record)
@@ -297,7 +301,7 @@ def _load_logging_config(log_config_path: str) -> None:
     logging.config.dictConfig(log_config)
 
 
-def _reload_logging_config(log_config_path):
+def _reload_logging_config(log_config_path: Optional[str]) -> None:
     """
     Reload the log configuration from the file and apply it.
     """
@@ -311,8 +315,8 @@ def _reload_logging_config(log_config_path):
 
 def setup_logging(
     hs: "HomeServer",
-    config,
-    use_worker_options=False,
+    config: "HomeServerConfig",
+    use_worker_options: bool = False,
     logBeginner: LogBeginner = globalLogBeginner,
 ) -> None:
     """
diff --git a/synapse/config/oidc.py b/synapse/config/oidc.py
index 42f113cd24..79c400fe30 100644
--- a/synapse/config/oidc.py
+++ b/synapse/config/oidc.py
@@ -14,7 +14,7 @@
 # limitations under the License.
 
 from collections import Counter
-from typing import Collection, Iterable, List, Mapping, Optional, Tuple, Type
+from typing import Any, Collection, Iterable, List, Mapping, Optional, Tuple, Type
 
 import attr
 
@@ -36,7 +36,7 @@ LEGACY_USER_MAPPING_PROVIDER = "synapse.handlers.oidc_handler.JinjaOidcMappingPr
 class OIDCConfig(Config):
     section = "oidc"
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         self.oidc_providers = tuple(_parse_oidc_provider_configs(config))
         if not self.oidc_providers:
             return
@@ -66,7 +66,7 @@ class OIDCConfig(Config):
         # OIDC is enabled if we have a provider
         return bool(self.oidc_providers)
 
-    def generate_config_section(self, config_dir_path, server_name, **kwargs):
+    def generate_config_section(self, config_dir_path, server_name, **kwargs) -> str:
         return """\
         # List of OpenID Connect (OIDC) / OAuth 2.0 identity providers, for registration
         # and login.
@@ -495,89 +495,89 @@ def _parse_oidc_config_dict(
     )
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class OidcProviderClientSecretJwtKey:
     # a pem-encoded signing key
-    key = attr.ib(type=str)
+    key: str
 
     # properties to include in the JWT header
-    jwt_header = attr.ib(type=Mapping[str, str])
+    jwt_header: Mapping[str, str]
 
     # properties to include in the JWT payload.
-    jwt_payload = attr.ib(type=Mapping[str, str])
+    jwt_payload: Mapping[str, str]
 
 
-@attr.s(slots=True, frozen=True)
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class OidcProviderConfig:
     # a unique identifier for this identity provider. Used in the 'user_external_ids'
     # table, as well as the query/path parameter used in the login protocol.
-    idp_id = attr.ib(type=str)
+    idp_id: str
 
     # user-facing name for this identity provider.
-    idp_name = attr.ib(type=str)
+    idp_name: str
 
     # Optional MXC URI for icon for this IdP.
-    idp_icon = attr.ib(type=Optional[str])
+    idp_icon: Optional[str]
 
     # Optional brand identifier for this IdP.
-    idp_brand = attr.ib(type=Optional[str])
+    idp_brand: Optional[str]
 
     # whether the OIDC discovery mechanism is used to discover endpoints
-    discover = attr.ib(type=bool)
+    discover: bool
 
     # the OIDC issuer. Used to validate tokens and (if discovery is enabled) to
     # discover the provider's endpoints.
-    issuer = attr.ib(type=str)
+    issuer: str
 
     # oauth2 client id to use
-    client_id = attr.ib(type=str)
+    client_id: str
 
     # oauth2 client secret to use. if `None`, use client_secret_jwt_key to generate
     # a secret.
-    client_secret = attr.ib(type=Optional[str])
+    client_secret: Optional[str]
 
     # key to use to construct a JWT to use as a client secret. May be `None` if
     # `client_secret` is set.
-    client_secret_jwt_key = attr.ib(type=Optional[OidcProviderClientSecretJwtKey])
+    client_secret_jwt_key: Optional[OidcProviderClientSecretJwtKey]
 
     # auth method to use when exchanging the token.
     # Valid values are 'client_secret_basic', 'client_secret_post' and
     # 'none'.
-    client_auth_method = attr.ib(type=str)
+    client_auth_method: str
 
     # list of scopes to request
-    scopes = attr.ib(type=Collection[str])
+    scopes: Collection[str]
 
     # the oauth2 authorization endpoint. Required if discovery is disabled.
-    authorization_endpoint = attr.ib(type=Optional[str])
+    authorization_endpoint: Optional[str]
 
     # the oauth2 token endpoint. Required if discovery is disabled.
-    token_endpoint = attr.ib(type=Optional[str])
+    token_endpoint: Optional[str]
 
     # the OIDC userinfo endpoint. Required if discovery is disabled and the
     # "openid" scope is not requested.
-    userinfo_endpoint = attr.ib(type=Optional[str])
+    userinfo_endpoint: Optional[str]
 
     # URI where to fetch the JWKS. Required if discovery is disabled and the
     # "openid" scope is used.
-    jwks_uri = attr.ib(type=Optional[str])
+    jwks_uri: Optional[str]
 
     # Whether to skip metadata verification
-    skip_verification = attr.ib(type=bool)
+    skip_verification: bool
 
     # Whether to fetch the user profile from the userinfo endpoint. Valid
     # values are: "auto" or "userinfo_endpoint".
-    user_profile_method = attr.ib(type=str)
+    user_profile_method: str
 
     # whether to allow a user logging in via OIDC to match a pre-existing account
     # instead of failing
-    allow_existing_users = attr.ib(type=bool)
+    allow_existing_users: bool
 
     # the class of the user mapping provider
-    user_mapping_provider_class = attr.ib(type=Type)
+    user_mapping_provider_class: Type
 
     # the config of the user mapping provider
-    user_mapping_provider_config = attr.ib()
+    user_mapping_provider_config: Any
 
     # required attributes to require in userinfo to allow login/registration
-    attribute_requirements = attr.ib(type=List[SsoAttributeRequirement])
+    attribute_requirements: List[SsoAttributeRequirement]
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index 1ddad7cb70..47853199f4 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -1,4 +1,5 @@
 # Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -11,6 +12,7 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import argparse
 from typing import Optional
 
 from synapse.api.constants import RoomCreationPreset
@@ -362,7 +364,7 @@ class RegistrationConfig(Config):
         )
 
     @staticmethod
-    def add_arguments(parser):
+    def add_arguments(parser: argparse.ArgumentParser) -> None:
         reg_group = parser.add_argument_group("registration")
         reg_group.add_argument(
             "--enable-registration",
@@ -371,6 +373,6 @@ class RegistrationConfig(Config):
             help="Enable registration for new users.",
         )
 
-    def read_arguments(self, args):
+    def read_arguments(self, args: argparse.Namespace) -> None:
         if args.enable_registration is not None:
             self.enable_registration = strtobool(str(args.enable_registration))
diff --git a/synapse/config/repository.py b/synapse/config/repository.py
index 69906a98d4..b129b9dd68 100644
--- a/synapse/config/repository.py
+++ b/synapse/config/repository.py
@@ -15,11 +15,12 @@
 import logging
 import os
 from collections import namedtuple
-from typing import Dict, List
+from typing import Dict, List, Tuple
 from urllib.request import getproxies_environment  # type: ignore
 
 from synapse.config.server import DEFAULT_IP_RANGE_BLACKLIST, generate_ip_set
 from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.types import JsonDict
 from synapse.util.module_loader import load_module
 
 from ._base import Config, ConfigError
@@ -57,7 +58,9 @@ MediaStorageProviderConfig = namedtuple(
 )
 
 
-def parse_thumbnail_requirements(thumbnail_sizes):
+def parse_thumbnail_requirements(
+    thumbnail_sizes: List[JsonDict],
+) -> Dict[str, Tuple[ThumbnailRequirement, ...]]:
     """Takes a list of dictionaries with "width", "height", and "method" keys
     and creates a map from image media types to the thumbnail size, thumbnailing
     method, and thumbnail media type to precalculate
@@ -69,7 +72,7 @@ def parse_thumbnail_requirements(thumbnail_sizes):
         Dictionary mapping from media type string to list of
         ThumbnailRequirement tuples.
     """
-    requirements: Dict[str, List] = {}
+    requirements: Dict[str, List[ThumbnailRequirement]] = {}
     for size in thumbnail_sizes:
         width = size["width"]
         height = size["height"]
diff --git a/synapse/config/saml2.py b/synapse/config/saml2.py
index ba2b0905ff..ec9d9f65e7 100644
--- a/synapse/config/saml2.py
+++ b/synapse/config/saml2.py
@@ -1,5 +1,5 @@
 # Copyright 2018 New Vector Ltd
-# Copyright 2019 The Matrix.org Foundation C.I.C.
+# Copyright 2019-2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -14,10 +14,11 @@
 # limitations under the License.
 
 import logging
-from typing import Any, List
+from typing import Any, List, Set
 
 from synapse.config.sso import SsoAttributeRequirement
 from synapse.python_dependencies import DependencyException, check_requirements
+from synapse.types import JsonDict
 from synapse.util.module_loader import load_module, load_python_module
 
 from ._base import Config, ConfigError
@@ -33,7 +34,7 @@ LEGACY_USER_MAPPING_PROVIDER = (
 )
 
 
-def _dict_merge(merge_dict, into_dict):
+def _dict_merge(merge_dict: dict, into_dict: dict) -> None:
     """Do a deep merge of two dicts
 
     Recursively merges `merge_dict` into `into_dict`:
@@ -43,8 +44,8 @@ def _dict_merge(merge_dict, into_dict):
         the value from `merge_dict`.
 
     Args:
-        merge_dict (dict): dict to merge
-        into_dict (dict): target dict
+        merge_dict: dict to merge
+        into_dict: target dict to be modified
     """
     for k, v in merge_dict.items():
         if k not in into_dict:
@@ -64,7 +65,7 @@ def _dict_merge(merge_dict, into_dict):
 class SAML2Config(Config):
     section = "saml2"
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         self.saml2_enabled = False
 
         saml2_config = config.get("saml2_config")
@@ -183,8 +184,8 @@ class SAML2Config(Config):
         )
 
     def _default_saml_config_dict(
-        self, required_attributes: set, optional_attributes: set
-    ):
+        self, required_attributes: Set[str], optional_attributes: Set[str]
+    ) -> JsonDict:
         """Generate a configuration dictionary with required and optional attributes that
         will be needed to process new user registration
 
@@ -195,7 +196,7 @@ class SAML2Config(Config):
                 additional information to Synapse user accounts, but are not required
 
         Returns:
-            dict: A SAML configuration dictionary
+            A SAML configuration dictionary
         """
         import saml2
 
@@ -222,7 +223,7 @@ class SAML2Config(Config):
             },
         }
 
-    def generate_config_section(self, config_dir_path, server_name, **kwargs):
+    def generate_config_section(self, config_dir_path, server_name, **kwargs) -> str:
         return """\
         ## Single sign-on integration ##
 
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 8445e9dd05..ba5b954263 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -12,6 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import argparse
 import itertools
 import logging
 import os.path
@@ -27,6 +28,7 @@ from netaddr import AddrFormatError, IPNetwork, IPSet
 from twisted.conch.ssh.keys import Key
 
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
+from synapse.types import JsonDict
 from synapse.util.module_loader import load_module
 from synapse.util.stringutils import parse_and_validate_server_name
 
@@ -1223,7 +1225,7 @@ class ServerConfig(Config):
             % locals()
         )
 
-    def read_arguments(self, args):
+    def read_arguments(self, args: argparse.Namespace) -> None:
         if args.manhole is not None:
             self.manhole = args.manhole
         if args.daemonize is not None:
@@ -1232,7 +1234,7 @@ class ServerConfig(Config):
             self.print_pidfile = args.print_pidfile
 
     @staticmethod
-    def add_arguments(parser):
+    def add_arguments(parser: argparse.ArgumentParser) -> None:
         server_group = parser.add_argument_group("server")
         server_group.add_argument(
             "-D",
@@ -1274,14 +1276,16 @@ class ServerConfig(Config):
             )
 
 
-def is_threepid_reserved(reserved_threepids, threepid):
+def is_threepid_reserved(
+    reserved_threepids: List[JsonDict], threepid: JsonDict
+) -> bool:
     """Check the threepid against the reserved threepid config
     Args:
-        reserved_threepids([dict]) - list of reserved threepids
-        threepid(dict) - The threepid to test for
+        reserved_threepids: List of reserved threepids
+        threepid: The threepid to test for
 
     Returns:
-        boolean Is the threepid undertest reserved_user
+        Is the threepid undertest reserved_user
     """
 
     for tp in reserved_threepids:
@@ -1290,7 +1294,9 @@ def is_threepid_reserved(reserved_threepids, threepid):
     return False
 
 
-def read_gc_thresholds(thresholds):
+def read_gc_thresholds(
+    thresholds: Optional[List[Any]],
+) -> Optional[Tuple[int, int, int]]:
     """Reads the three integer thresholds for garbage collection. Ensures that
     the thresholds are integers if thresholds are supplied.
     """
diff --git a/synapse/config/sso.py b/synapse/config/sso.py
index 60aacb13ea..e4a4243261 100644
--- a/synapse/config/sso.py
+++ b/synapse/config/sso.py
@@ -1,4 +1,4 @@
-# Copyright 2020 The Matrix.org Foundation C.I.C.
+# Copyright 2020-2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -29,13 +29,13 @@ https://matrix-org.github.io/synapse/latest/templates.html
 ---------------------------------------------------------------------------------------"""
 
 
-@attr.s(frozen=True)
+@attr.s(frozen=True, auto_attribs=True)
 class SsoAttributeRequirement:
     """Object describing a single requirement for SSO attributes."""
 
-    attribute = attr.ib(type=str)
+    attribute: str
     # If a value is not given, than the attribute must simply exist.
-    value = attr.ib(type=Optional[str])
+    value: Optional[str]
 
     JSON_SCHEMA = {
         "type": "object",
@@ -49,7 +49,7 @@ class SSOConfig(Config):
 
     section = "sso"
 
-    def read_config(self, config, **kwargs):
+    def read_config(self, config, **kwargs) -> None:
         sso_config: Dict[str, Any] = config.get("sso") or {}
 
         # The sso-specific template_dir
@@ -106,7 +106,7 @@ class SSOConfig(Config):
         )
         self.sso_client_whitelist.append(login_fallback_url)
 
-    def generate_config_section(self, **kwargs):
+    def generate_config_section(self, **kwargs) -> str:
         return """\
         # Additional settings to use with single-sign on systems such as OpenID Connect,
         # SAML2 and CAS.
diff --git a/synapse/config/workers.py b/synapse/config/workers.py
index 4507992031..576f519188 100644
--- a/synapse/config/workers.py
+++ b/synapse/config/workers.py
@@ -1,4 +1,5 @@
 # Copyright 2016 OpenMarket Ltd
+# Copyright 2021 The Matrix.org Foundation C.I.C.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -12,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import argparse
 from typing import List, Union
 
 import attr
@@ -343,7 +345,7 @@ class WorkerConfig(Config):
         #worker_replication_secret: ""
         """
 
-    def read_arguments(self, args):
+    def read_arguments(self, args: argparse.Namespace) -> None:
         # We support a bunch of command line arguments that override options in
         # the config. A lot of these options have a worker_* prefix when running
         # on workers so we also have to override them when command line options