Replace `room_invite_state_types` with `room_prejoin_state` (#9700)

`room_invite_state_types` was inconvenient as a configuration setting, because
anyone that ever set it would not receive any new types that were added to the
defaults. Here, we deprecate the old setting, and replace it with a couple of
new settings under `room_prejoin_state`.

8 files changed, 144 insertions, 43 deletions

diff --git a/changelog.d/9700.feature b/changelog.d/9700.feature
new file mode 100644
index 0000000000..037de8367f
--- /dev/null
+++ b/changelog.d/9700.feature
@@ -0,0 +1 @@
+Replace the `room_invite_state_types` configuration setting with `room_prejoin_state`.
diff --git a/docker/conf/homeserver.yaml b/docker/conf/homeserver.yaml
index 0dea62a87d..a792899540 100644
--- a/docker/conf/homeserver.yaml
+++ b/docker/conf/homeserver.yaml
@@ -173,18 +173,10 @@ report_stats: False
 
 ## API Configuration ##
 
-room_invite_state_types:
-    - "m.room.join_rules"
-    - "m.room.canonical_alias"
-    - "m.room.avatar"
-    - "m.room.name"
-
 {% if SYNAPSE_APPSERVICES %}
 app_service_config_files:
 {% for appservice in SYNAPSE_APPSERVICES %}    - "{{ appservice }}"
 {% endfor %}
-{% else %}
-app_service_config_files: []
 {% endif %}
 
 macaroon_secret_key: "{{ SYNAPSE_MACAROON_SECRET_KEY }}"
diff --git a/docs/code_style.md b/docs/code_style.md
index 190f8ab2de..28fb7277c4 100644
--- a/docs/code_style.md
+++ b/docs/code_style.md
@@ -128,6 +128,9 @@ Some guidelines follow:
     will be if no sub-options are enabled).
 -   Lines should be wrapped at 80 characters.
 -   Use two-space indents.
+-   `true` and `false` are spelt thus (as opposed to `True`, etc.)
+-   Use single quotes (`'`) rather than double-quotes (`"`) or backticks
+    (`` ` ``) to refer to configuration options.
 
 Example:
 
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 17cda71adc..c73ea6b161 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -1451,14 +1451,31 @@ metrics_flags:
 
 ## API Configuration ##
 
-# A list of event types that will be included in the room_invite_state
-#
-#room_invite_state_types:
-#  - "m.room.join_rules"
-#  - "m.room.canonical_alias"
-#  - "m.room.avatar"
-#  - "m.room.encryption"
-#  - "m.room.name"
+# Controls for the state that is shared with users who receive an invite
+# to a room
+#
+room_prejoin_state:
+   # By default, the following state event types are shared with users who
+   # receive invites to the room:
+   #
+   # - m.room.join_rules
+   # - m.room.canonical_alias
+   # - m.room.avatar
+   # - m.room.encryption
+   # - m.room.name
+   #
+   # Uncomment the following to disable these defaults (so that only the event
+   # types listed in 'additional_event_types' are shared). Defaults to 'false'.
+   #
+   #disable_default_event_types: true
+
+   # Additional state event types to share with users when they are invited
+   # to a room.
+   #
+   # By default, this list is empty (so only the default event types are shared).
+   #
+   #additional_event_types:
+   #  - org.example.custom.event.type
 
 
 # A list of application service config files to use
diff --git a/synapse/config/api.py b/synapse/config/api.py
index 74cd53a8ed..91387a7f0e 100644
--- a/synapse/config/api.py
+++ b/synapse/config/api.py
@@ -1,4 +1,4 @@
-# Copyright 2015, 2016 OpenMarket Ltd
+# Copyright 2015-2021 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.
@@ -12,38 +12,127 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import logging
+from typing import Iterable
+
 from synapse.api.constants import EventTypes
+from synapse.config._base import Config, ConfigError
+from synapse.config._util import validate_config
+from synapse.types import JsonDict
 
-from ._base import Config
+logger = logging.getLogger(__name__)
 
 
 class ApiConfig(Config):
     section = "api"
 
-    def read_config(self, config, **kwargs):
-        self.room_invite_state_types = config.get(
-            "room_invite_state_types",
-            [
-                EventTypes.JoinRules,
-                EventTypes.CanonicalAlias,
-                EventTypes.RoomAvatar,
-                EventTypes.RoomEncryption,
-                EventTypes.Name,
-            ],
+    def read_config(self, config: JsonDict, **kwargs):
+        validate_config(_MAIN_SCHEMA, config, ())
+        self.room_prejoin_state = list(self._get_prejoin_state_types(config))
+
+    def generate_config_section(cls, **kwargs) -> str:
+        formatted_default_state_types = "\n".join(
+            "           # - %s" % (t,) for t in _DEFAULT_PREJOIN_STATE_TYPES
         )
 
-    def generate_config_section(cls, **kwargs):
         return """\
         ## API Configuration ##
 
-        # A list of event types that will be included in the room_invite_state
+        # Controls for the state that is shared with users who receive an invite
+        # to a room
         #
-        #room_invite_state_types:
-        #  - "{JoinRules}"
-        #  - "{CanonicalAlias}"
-        #  - "{RoomAvatar}"
-        #  - "{RoomEncryption}"
-        #  - "{Name}"
-        """.format(
-            **vars(EventTypes)
-        )
+        room_prejoin_state:
+           # By default, the following state event types are shared with users who
+           # receive invites to the room:
+           #
+%(formatted_default_state_types)s
+           #
+           # Uncomment the following to disable these defaults (so that only the event
+           # types listed in 'additional_event_types' are shared). Defaults to 'false'.
+           #
+           #disable_default_event_types: true
+
+           # Additional state event types to share with users when they are invited
+           # to a room.
+           #
+           # By default, this list is empty (so only the default event types are shared).
+           #
+           #additional_event_types:
+           #  - org.example.custom.event.type
+        """ % {
+            "formatted_default_state_types": formatted_default_state_types
+        }
+
+    def _get_prejoin_state_types(self, config: JsonDict) -> Iterable[str]:
+        """Get the event types to include in the prejoin state
+
+        Parses the config and returns an iterable of the event types to be included.
+        """
+        room_prejoin_state_config = config.get("room_prejoin_state") or {}
+
+        # backwards-compatibility support for room_invite_state_types
+        if "room_invite_state_types" in config:
+            # if both "room_invite_state_types" and "room_prejoin_state" are set, then
+            # we don't really know what to do.
+            if room_prejoin_state_config:
+                raise ConfigError(
+                    "Can't specify both 'room_invite_state_types' and 'room_prejoin_state' "
+                    "in config"
+                )
+
+            logger.warning(_ROOM_INVITE_STATE_TYPES_WARNING)
+
+            yield from config["room_invite_state_types"]
+            return
+
+        if not room_prejoin_state_config.get("disable_default_event_types"):
+            yield from _DEFAULT_PREJOIN_STATE_TYPES
+
+        yield from room_prejoin_state_config.get("additional_event_types", [])
+
+
+_ROOM_INVITE_STATE_TYPES_WARNING = """\
+WARNING: The 'room_invite_state_types' configuration setting is now deprecated,
+and replaced with 'room_prejoin_state'. New features may not work correctly
+unless 'room_invite_state_types' is removed. See the sample configuration file for
+details of 'room_prejoin_state'.
+--------------------------------------------------------------------------------
+"""
+
+_DEFAULT_PREJOIN_STATE_TYPES = [
+    EventTypes.JoinRules,
+    EventTypes.CanonicalAlias,
+    EventTypes.RoomAvatar,
+    EventTypes.RoomEncryption,
+    EventTypes.Name,
+]
+
+
+# room_prejoin_state can either be None (as it is in the default config), or
+# an object containing other config settings
+_ROOM_PREJOIN_STATE_CONFIG_SCHEMA = {
+    "oneOf": [
+        {
+            "type": "object",
+            "properties": {
+                "disable_default_event_types": {"type": "boolean"},
+                "additional_event_types": {
+                    "type": "array",
+                    "items": {"type": "string"},
+                },
+            },
+        },
+        {"type": "null"},
+    ]
+}
+
+# the legacy room_invite_state_types setting
+_ROOM_INVITE_STATE_TYPES_SCHEMA = {"type": "array", "items": {"type": "string"}}
+
+_MAIN_SCHEMA = {
+    "type": "object",
+    "properties": {
+        "room_prejoin_state": _ROOM_PREJOIN_STATE_CONFIG_SCHEMA,
+        "room_invite_state_types": _ROOM_INVITE_STATE_TYPES_SCHEMA,
+    },
+}
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 1b7c065b34..6069968f7f 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -385,7 +385,7 @@ class EventCreationHandler:
         self._events_shard_config = self.config.worker.events_shard_config
         self._instance_name = hs.get_instance_name()
 
-        self.room_invite_state_types = self.hs.config.room_invite_state_types
+        self.room_invite_state_types = self.hs.config.api.room_prejoin_state
 
         self.membership_types_to_include_profile_data_in = (
             {Membership.JOIN, Membership.INVITE}
diff --git a/synapse/storage/databases/main/events_worker.py b/synapse/storage/databases/main/events_worker.py
index 952d4969b2..c00780969f 100644
--- a/synapse/storage/databases/main/events_worker.py
+++ b/synapse/storage/databases/main/events_worker.py
@@ -16,7 +16,7 @@
 import logging
 import threading
 from collections import namedtuple
-from typing import Dict, Iterable, List, Optional, Tuple, overload
+from typing import Container, Dict, Iterable, List, Optional, Tuple, overload
 
 from constantly import NamedConstant, Names
 from typing_extensions import Literal
@@ -544,7 +544,7 @@ class EventsWorkerStore(SQLBaseStore):
     async def get_stripped_room_state_from_event_context(
         self,
         context: EventContext,
-        state_types_to_include: List[EventTypes],
+        state_types_to_include: Container[str],
         membership_user_id: Optional[str] = None,
     ) -> List[JsonDict]:
         """
diff --git a/tests/utils.py b/tests/utils.py
index be80b13760..a141ee6496 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -122,7 +122,6 @@ def default_config(name, parse=False):
         "enable_registration_captcha": False,
         "macaroon_secret_key": "not even a little secret",
         "trusted_third_party_id_servers": [],
-        "room_invite_state_types": [],
         "password_providers": [],
         "worker_replication_url": "",
         "worker_app": None,