Collect room-version variations into one place (#4969)

Collect all the things that make room-versions different to one another into
one place, so that it's easier to define new room versions.

28 files changed, 222 insertions, 168 deletions

diff --git a/changelog.d/4969.misc b/changelog.d/4969.misc
new file mode 100644
index 0000000000..e3a3214e6b
--- /dev/null
+++ b/changelog.d/4969.misc
@@ -0,0 +1,2 @@
+Refactor room version definitions.
+
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index f47c33a074..dc913feeee 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -102,46 +102,6 @@ class ThirdPartyEntityKind(object):
     LOCATION = "location"
 
 
-class RoomVersions(object):
-    V1 = "1"
-    V2 = "2"
-    V3 = "3"
-    STATE_V2_TEST = "state-v2-test"
-
-
-class RoomDisposition(object):
-    STABLE = "stable"
-    UNSTABLE = "unstable"
-
-
-# the version we will give rooms which are created on this server
-DEFAULT_ROOM_VERSION = RoomVersions.V1
-
-# vdh-test-version is a placeholder to get room versioning support working and tested
-# until we have a working v2.
-KNOWN_ROOM_VERSIONS = {
-    RoomVersions.V1,
-    RoomVersions.V2,
-    RoomVersions.V3,
-    RoomVersions.STATE_V2_TEST,
-    RoomVersions.V3,
-}
-
-
-class EventFormatVersions(object):
-    """This is an internal enum for tracking the version of the event format,
-    independently from the room version.
-    """
-    V1 = 1
-    V2 = 2
-
-
-KNOWN_EVENT_FORMAT_VERSIONS = {
-    EventFormatVersions.V1,
-    EventFormatVersions.V2,
-}
-
-
 ServerNoticeMsgType = "m.server_notice"
 ServerNoticeLimitReached = "m.server_notice.usage_limit_reached"
 
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
new file mode 100644
index 0000000000..e77abe1040
--- /dev/null
+++ b/synapse/api/room_versions.py
@@ -0,0 +1,91 @@
+# -*- coding: utf-8 -*-
+# Copyright 2019 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# 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 attr
+
+
+class EventFormatVersions(object):
+    """This is an internal enum for tracking the version of the event format,
+    independently from the room version.
+    """
+    V1 = 1   # $id:server format
+    V2 = 2   # MSC1659-style $hash format: introduced for room v3
+
+
+KNOWN_EVENT_FORMAT_VERSIONS = {
+    EventFormatVersions.V1,
+    EventFormatVersions.V2,
+}
+
+
+class StateResolutionVersions(object):
+    """Enum to identify the state resolution algorithms"""
+    V1 = 1   # room v1 state res
+    V2 = 2   # MSC1442 state res: room v2 and later
+
+
+class RoomDisposition(object):
+    STABLE = "stable"
+    UNSTABLE = "unstable"
+
+
+@attr.s(slots=True, frozen=True)
+class RoomVersion(object):
+    """An object which describes the unique attributes of a room version."""
+
+    identifier = attr.ib()      # str; the identifier for this version
+    disposition = attr.ib()     # str; one of the RoomDispositions
+    event_format = attr.ib()    # int; one of the EventFormatVersions
+    state_res = attr.ib()       # int; one of the StateResolutionVersions
+
+
+class RoomVersions(object):
+    V1 = RoomVersion(
+        "1",
+        RoomDisposition.STABLE,
+        EventFormatVersions.V1,
+        StateResolutionVersions.V1,
+    )
+    STATE_V2_TEST = RoomVersion(
+        "state-v2-test",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.V1,
+        StateResolutionVersions.V2,
+    )
+    V2 = RoomVersion(
+        "2",
+        RoomDisposition.STABLE,
+        EventFormatVersions.V1,
+        StateResolutionVersions.V2,
+    )
+    V3 = RoomVersion(
+        "3",
+        RoomDisposition.STABLE,
+        EventFormatVersions.V2,
+        StateResolutionVersions.V2,
+    )
+
+
+# the version we will give rooms which are created on this server
+DEFAULT_ROOM_VERSION = RoomVersions.V1
+
+
+KNOWN_ROOM_VERSIONS = {
+    v.identifier: v for v in (
+        RoomVersions.V1,
+        RoomVersions.V2,
+        RoomVersions.V3,
+        RoomVersions.STATE_V2_TEST,
+    )
+}   # type: dict[str, RoomVersion]
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
index 8f9e330da5..203490fc36 100644
--- a/synapse/event_auth.py
+++ b/synapse/event_auth.py
@@ -20,15 +20,9 @@ from signedjson.key import decode_verify_key_bytes
 from signedjson.sign import SignatureVerifyException, verify_signed_json
 from unpaddedbase64 import decode_base64
 
-from synapse.api.constants import (
-    KNOWN_ROOM_VERSIONS,
-    EventFormatVersions,
-    EventTypes,
-    JoinRules,
-    Membership,
-    RoomVersions,
-)
+from synapse.api.constants import EventTypes, JoinRules, Membership
 from synapse.api.errors import AuthError, EventSizeError, SynapseError
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, EventFormatVersions
 from synapse.types import UserID, get_domain_from_id
 
 logger = logging.getLogger(__name__)
@@ -452,16 +446,18 @@ def check_redaction(room_version, event, auth_events):
     if user_level >= redact_level:
         return False
 
-    if room_version in (RoomVersions.V1, RoomVersions.V2,):
+    v = KNOWN_ROOM_VERSIONS.get(room_version)
+    if not v:
+        raise RuntimeError("Unrecognized room version %r" % (room_version,))
+
+    if v.event_format == EventFormatVersions.V1:
         redacter_domain = get_domain_from_id(event.event_id)
         redactee_domain = get_domain_from_id(event.redacts)
         if redacter_domain == redactee_domain:
             return True
-    elif room_version == RoomVersions.V3:
+    else:
         event.internal_metadata.recheck_redaction = True
         return True
-    else:
-        raise RuntimeError("Unrecognized room version %r" % (room_version,))
 
     raise AuthError(
         403,
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index fafa135182..12056d5be2 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -21,7 +21,7 @@ import six
 
 from unpaddedbase64 import encode_base64
 
-from synapse.api.constants import KNOWN_ROOM_VERSIONS, EventFormatVersions, RoomVersions
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, EventFormatVersions
 from synapse.util.caches import intern_dict
 from synapse.util.frozenutils import freeze
 
@@ -351,18 +351,13 @@ def room_version_to_event_format(room_version):
     Returns:
         int
     """
-    if room_version not in KNOWN_ROOM_VERSIONS:
+    v = KNOWN_ROOM_VERSIONS.get(room_version)
+
+    if not v:
         # We should have already checked version, so this should not happen
         raise RuntimeError("Unrecognized room version %s" % (room_version,))
 
-    if room_version in (
-        RoomVersions.V1, RoomVersions.V2, RoomVersions.STATE_V2_TEST,
-    ):
-        return EventFormatVersions.V1
-    elif room_version in (RoomVersions.V3,):
-        return EventFormatVersions.V2
-    else:
-        raise RuntimeError("Unrecognized room version %s" % (room_version,))
+    return v.event_format
 
 
 def event_type_from_format_version(format_version):
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index 06e01be918..fba27177c7 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -17,21 +17,17 @@ import attr
 
 from twisted.internet import defer
 
-from synapse.api.constants import (
+from synapse.api.constants import MAX_DEPTH
+from synapse.api.room_versions import (
     KNOWN_EVENT_FORMAT_VERSIONS,
     KNOWN_ROOM_VERSIONS,
-    MAX_DEPTH,
     EventFormatVersions,
 )
 from synapse.crypto.event_signing import add_hashes_and_signatures
 from synapse.types import EventID
 from synapse.util.stringutils import random_string
 
-from . import (
-    _EventInternalMetadata,
-    event_type_from_format_version,
-    room_version_to_event_format,
-)
+from . import _EventInternalMetadata, event_type_from_format_version
 
 
 @attr.s(slots=True, cmp=False, frozen=True)
@@ -170,21 +166,34 @@ class EventBuilderFactory(object):
     def new(self, room_version, key_values):
         """Generate an event builder appropriate for the given room version
 
+        Deprecated: use for_room_version with a RoomVersion object instead
+
         Args:
-            room_version (str): Version of the room that we're creating an
-                event builder for
+            room_version (str): Version of the room that we're creating an event builder
+                for
             key_values (dict): Fields used as the basis of the new event
 
         Returns:
             EventBuilder
         """
-
-        # There's currently only the one event version defined
-        if room_version not in KNOWN_ROOM_VERSIONS:
+        v = KNOWN_ROOM_VERSIONS.get(room_version)
+        if not v:
             raise Exception(
                 "No event format defined for version %r" % (room_version,)
             )
+        return self.for_room_version(v, key_values)
 
+    def for_room_version(self, room_version, key_values):
+        """Generate an event builder appropriate for the given room version
+
+        Args:
+            room_version (synapse.api.room_versions.RoomVersion):
+                Version of the room that we're creating an event builder for
+            key_values (dict): Fields used as the basis of the new event
+
+        Returns:
+            EventBuilder
+        """
         return EventBuilder(
             store=self.store,
             state=self.state,
@@ -192,7 +201,7 @@ class EventBuilderFactory(object):
             clock=self.clock,
             hostname=self.hostname,
             signing_key=self.signing_key,
-            format_version=room_version_to_event_format(room_version),
+            format_version=room_version.event_format,
             type=key_values["type"],
             state_key=key_values.get("state_key"),
             room_id=key_values["room_id"],
@@ -222,7 +231,6 @@ def create_local_event_from_event_dict(clock, hostname, signing_key,
         FrozenEvent
     """
 
-    # There's currently only the one event version defined
     if format_version not in KNOWN_EVENT_FORMAT_VERSIONS:
         raise Exception(
             "No event format defined for version %r" % (format_version,)
diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index a072674b02..514273c792 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -15,8 +15,9 @@
 
 from six import string_types
 
-from synapse.api.constants import EventFormatVersions, EventTypes, Membership
+from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import SynapseError
+from synapse.api.room_versions import EventFormatVersions
 from synapse.types import EventID, RoomID, UserID
 
 
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index a7a2ec4523..dfe6b4aa5c 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -20,8 +20,9 @@ import six
 from twisted.internet import defer
 from twisted.internet.defer import DeferredList
 
-from synapse.api.constants import MAX_DEPTH, EventTypes, Membership, RoomVersions
+from synapse.api.constants import MAX_DEPTH, EventTypes, Membership
 from synapse.api.errors import Codes, SynapseError
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, EventFormatVersions
 from synapse.crypto.event_signing import check_event_content_hash
 from synapse.events import event_type_from_format_version
 from synapse.events.utils import prune_event
@@ -274,9 +275,12 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
     # now let's look for events where the sender's domain is different to the
     # event id's domain (normally only the case for joins/leaves), and add additional
     # checks. Only do this if the room version has a concept of event ID domain
-    if room_version in (
-        RoomVersions.V1, RoomVersions.V2, RoomVersions.STATE_V2_TEST,
-    ):
+    # (ie, the room version uses old-style non-hash event IDs).
+    v = KNOWN_ROOM_VERSIONS.get(room_version)
+    if not v:
+        raise RuntimeError("Unrecognized room version %s" % (room_version,))
+
+    if v.event_format == EventFormatVersions.V1:
         pdus_to_check_event_id = [
             p for p in pdus_to_check
             if p.sender_domain != get_domain_from_id(p.pdu.event_id)
@@ -289,10 +293,6 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
 
         for p, d in zip(pdus_to_check_event_id, more_deferreds):
             p.deferreds.append(d)
-    elif room_version in (RoomVersions.V3,):
-        pass  # No further checks needed, as event IDs are hashes here
-    else:
-        raise RuntimeError("Unrecognized room version %s" % (room_version,))
 
     # replace lists of deferreds with single Deferreds
     return [_flatten_deferred_list(p.deferreds) for p in pdus_to_check]
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 58e04d81ab..f3fc897a0a 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -25,12 +25,7 @@ from prometheus_client import Counter
 
 from twisted.internet import defer
 
-from synapse.api.constants import (
-    KNOWN_ROOM_VERSIONS,
-    EventTypes,
-    Membership,
-    RoomVersions,
-)
+from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import (
     CodeMessageException,
     Codes,
@@ -38,6 +33,11 @@ from synapse.api.errors import (
     HttpResponseException,
     SynapseError,
 )
+from synapse.api.room_versions import (
+    KNOWN_ROOM_VERSIONS,
+    EventFormatVersions,
+    RoomVersions,
+)
 from synapse.events import builder, room_version_to_event_format
 from synapse.federation.federation_base import FederationBase, event_from_pdu_json
 from synapse.util import logcontext, unwrapFirstError
@@ -570,7 +570,7 @@ class FederationClient(FederationBase):
             Deferred[tuple[str, FrozenEvent, int]]: resolves to a tuple of
             `(origin, event, event_format)` where origin is the remote
             homeserver which generated the event, and event_format is one of
-            `synapse.api.constants.EventFormatVersions`.
+            `synapse.api.room_versions.EventFormatVersions`.
 
             Fails with a ``SynapseError`` if the chosen remote server
             returns a 300/400 code.
@@ -592,7 +592,7 @@ class FederationClient(FederationBase):
 
             # Note: If not supplied, the room version may be either v1 or v2,
             # however either way the event format version will be v1.
-            room_version = ret.get("room_version", RoomVersions.V1)
+            room_version = ret.get("room_version", RoomVersions.V1.identifier)
             event_format = room_version_to_event_format(room_version)
 
             pdu_dict = ret.get("event", None)
@@ -695,7 +695,9 @@ class FederationClient(FederationBase):
             room_version = None
             for e in state:
                 if (e.type, e.state_key) == (EventTypes.Create, ""):
-                    room_version = e.content.get("room_version", RoomVersions.V1)
+                    room_version = e.content.get(
+                        "room_version", RoomVersions.V1.identifier
+                    )
                     break
 
             if room_version is None:
@@ -802,11 +804,10 @@ class FederationClient(FederationBase):
                     raise err
 
                 # Otherwise, we assume that the remote server doesn't understand
-                # the v2 invite API.
-
-                if room_version in (RoomVersions.V1, RoomVersions.V2):
-                    pass  # We'll fall through
-                else:
+                # the v2 invite API. That's ok provided the room uses old-style event
+                # IDs.
+                v = KNOWN_ROOM_VERSIONS.get(room_version)
+                if v.event_format != EventFormatVersions.V1:
                     raise SynapseError(
                         400,
                         "User's homeserver does not support this room version",
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 81f3b4b1ff..df60828dba 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -25,7 +25,7 @@ from twisted.internet import defer
 from twisted.internet.abstract import isIPAddress
 from twisted.python import failure
 
-from synapse.api.constants import KNOWN_ROOM_VERSIONS, EventTypes, Membership
+from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import (
     AuthError,
     Codes,
@@ -34,6 +34,7 @@ from synapse.api.errors import (
     NotFoundError,
     SynapseError,
 )
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.crypto.event_signing import compute_event_signature
 from synapse.events import room_version_to_event_format
 from synapse.federation.federation_base import FederationBase, event_from_pdu_json
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index efb6bdca48..452599e1a1 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -21,8 +21,8 @@ import re
 from twisted.internet import defer
 
 import synapse
-from synapse.api.constants import RoomVersions
 from synapse.api.errors import Codes, FederationDeniedError, SynapseError
+from synapse.api.room_versions import RoomVersions
 from synapse.api.urls import FEDERATION_V1_PREFIX, FEDERATION_V2_PREFIX
 from synapse.http.endpoint import parse_and_validate_server_name
 from synapse.http.server import JsonResource
@@ -513,7 +513,7 @@ class FederationV1InviteServlet(BaseFederationServlet):
         # state resolution algorithm, and we don't use that for processing
         # invites
         content = yield self.handler.on_invite_request(
-            origin, content, room_version=RoomVersions.V1,
+            origin, content, room_version=RoomVersions.V1.identifier,
         )
 
         # V1 federation API is defined to return a content of `[200, {...}]`
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 9eaf2d3e18..0684778882 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -29,13 +29,7 @@ from unpaddedbase64 import decode_base64
 
 from twisted.internet import defer
 
-from synapse.api.constants import (
-    KNOWN_ROOM_VERSIONS,
-    EventTypes,
-    Membership,
-    RejectedReason,
-    RoomVersions,
-)
+from synapse.api.constants import EventTypes, Membership, RejectedReason
 from synapse.api.errors import (
     AuthError,
     CodeMessageException,
@@ -44,6 +38,7 @@ from synapse.api.errors import (
     StoreError,
     SynapseError,
 )
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersions
 from synapse.crypto.event_signing import compute_event_signature
 from synapse.event_auth import auth_types_for_event
 from synapse.events.validator import EventValidator
@@ -1733,7 +1728,9 @@ class FederationHandler(BaseHandler):
             # invalid, and it would fail auth checks anyway.
             raise SynapseError(400, "No create event in state")
 
-        room_version = create_event.content.get("room_version", RoomVersions.V1)
+        room_version = create_event.content.get(
+            "room_version", RoomVersions.V1.identifier,
+        )
 
         missing_auth_events = set()
         for e in itertools.chain(auth_events, state, [event]):
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 9b41c7b205..8bc7a7678a 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -22,7 +22,7 @@ from canonicaljson import encode_canonical_json, json
 from twisted.internet import defer
 from twisted.internet.defer import succeed
 
-from synapse.api.constants import EventTypes, Membership, RoomVersions
+from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import (
     AuthError,
     Codes,
@@ -30,6 +30,7 @@ from synapse.api.errors import (
     NotFoundError,
     SynapseError,
 )
+from synapse.api.room_versions import RoomVersions
 from synapse.api.urls import ConsentURIBuilder
 from synapse.events.utils import serialize_event
 from synapse.events.validator import EventValidator
@@ -603,7 +604,9 @@ class EventCreationHandler(object):
         """
 
         if event.is_state() and (event.type, event.state_key) == (EventTypes.Create, ""):
-            room_version = event.content.get("room_version", RoomVersions.V1)
+            room_version = event.content.get(
+                "room_version", RoomVersions.V1.identifier
+            )
         else:
             room_version = yield self.store.get_room_version(event.room_id)
 
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 67b15697fd..c3dcfec247 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -25,14 +25,9 @@ from six import iteritems, string_types
 
 from twisted.internet import defer
 
-from synapse.api.constants import (
-    DEFAULT_ROOM_VERSION,
-    KNOWN_ROOM_VERSIONS,
-    EventTypes,
-    JoinRules,
-    RoomCreationPreset,
-)
+from synapse.api.constants import EventTypes, JoinRules, RoomCreationPreset
 from synapse.api.errors import AuthError, Codes, NotFoundError, StoreError, SynapseError
+from synapse.api.room_versions import DEFAULT_ROOM_VERSION, KNOWN_ROOM_VERSIONS
 from synapse.storage.state import StateFilter
 from synapse.types import RoomAlias, RoomID, RoomStreamToken, StreamToken, UserID
 from synapse.util import stringutils
@@ -479,7 +474,7 @@ class RoomCreationHandler(BaseHandler):
         if ratelimit:
             yield self.ratelimit(requester)
 
-        room_version = config.get("room_version", DEFAULT_ROOM_VERSION)
+        room_version = config.get("room_version", DEFAULT_ROOM_VERSION.identifier)
         if not isinstance(room_version, string_types):
             raise SynapseError(
                 400,
diff --git a/synapse/rest/client/v2_alpha/capabilities.py b/synapse/rest/client/v2_alpha/capabilities.py
index 373f95126e..a868d06098 100644
--- a/synapse/rest/client/v2_alpha/capabilities.py
+++ b/synapse/rest/client/v2_alpha/capabilities.py
@@ -16,7 +16,7 @@ import logging
 
 from twisted.internet import defer
 
-from synapse.api.constants import DEFAULT_ROOM_VERSION, RoomDisposition, RoomVersions
+from synapse.api.room_versions import DEFAULT_ROOM_VERSION, KNOWN_ROOM_VERSIONS
 from synapse.http.servlet import RestServlet
 
 from ._base import client_v2_patterns
@@ -48,12 +48,10 @@ class CapabilitiesRestServlet(RestServlet):
         response = {
             "capabilities": {
                 "m.room_versions": {
-                    "default": DEFAULT_ROOM_VERSION,
+                    "default": DEFAULT_ROOM_VERSION.identifier,
                     "available": {
-                        RoomVersions.V1: RoomDisposition.STABLE,
-                        RoomVersions.V2: RoomDisposition.STABLE,
-                        RoomVersions.STATE_V2_TEST: RoomDisposition.UNSTABLE,
-                        RoomVersions.V3: RoomDisposition.STABLE,
+                        v.identifier: v.disposition
+                        for v in KNOWN_ROOM_VERSIONS.values()
                     },
                 },
                 "m.change_password": {"enabled": change_password},
diff --git a/synapse/rest/client/v2_alpha/room_upgrade_rest_servlet.py b/synapse/rest/client/v2_alpha/room_upgrade_rest_servlet.py
index e6356101fd..3db7ff8d1b 100644
--- a/synapse/rest/client/v2_alpha/room_upgrade_rest_servlet.py
+++ b/synapse/rest/client/v2_alpha/room_upgrade_rest_servlet.py
@@ -17,8 +17,8 @@ import logging
 
 from twisted.internet import defer
 
-from synapse.api.constants import KNOWN_ROOM_VERSIONS
 from synapse.api.errors import Codes, SynapseError
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
 from synapse.http.servlet import (
     RestServlet,
     assert_params_in_dict,
diff --git a/synapse/state/__init__.py b/synapse/state/__init__.py
index 68058f613c..52347fee34 100644
--- a/synapse/state/__init__.py
+++ b/synapse/state/__init__.py
@@ -24,7 +24,8 @@ from frozendict import frozendict
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventTypes, RoomVersions
+from synapse.api.constants import EventTypes
+from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, StateResolutionVersions
 from synapse.events.snapshot import EventContext
 from synapse.state import v1, v2
 from synapse.util.async_helpers import Linearizer
@@ -603,22 +604,15 @@ def resolve_events_with_store(room_version, state_sets, event_map, state_res_sto
         Deferred[dict[(str, str), str]]:
             a map from (type, state_key) to event_id.
     """
-    if room_version == RoomVersions.V1:
+    v = KNOWN_ROOM_VERSIONS[room_version]
+    if v.state_res == StateResolutionVersions.V1:
         return v1.resolve_events_with_store(
             state_sets, event_map, state_res_store.get_events,
         )
-    elif room_version in (
-        RoomVersions.STATE_V2_TEST, RoomVersions.V2, RoomVersions.V3,
-    ):
+    else:
         return v2.resolve_events_with_store(
             room_version, state_sets, event_map, state_res_store,
         )
-    else:
-        # This should only happen if we added a version but forgot to add it to
-        # the list above.
-        raise Exception(
-            "No state resolution algorithm defined for version %r" % (room_version,)
-        )
 
 
 @attr.s
diff --git a/synapse/state/v1.py b/synapse/state/v1.py
index 6d3afcae7c..29b4e86cfd 100644
--- a/synapse/state/v1.py
+++ b/synapse/state/v1.py
@@ -21,8 +21,9 @@ from six import iteritems, iterkeys, itervalues
 from twisted.internet import defer
 
 from synapse import event_auth
-from synapse.api.constants import EventTypes, RoomVersions
+from synapse.api.constants import EventTypes
 from synapse.api.errors import AuthError
+from synapse.api.room_versions import RoomVersions
 
 logger = logging.getLogger(__name__)
 
@@ -275,7 +276,9 @@ def _resolve_auth_events(events, auth_events):
         try:
             # The signatures have already been checked at this point
             event_auth.check(
-                RoomVersions.V1, event, auth_events,
+                RoomVersions.V1.identifier,
+                event,
+                auth_events,
                 do_sig_check=False,
                 do_size_check=False,
             )
@@ -291,7 +294,9 @@ def _resolve_normal_events(events, auth_events):
         try:
             # The signatures have already been checked at this point
             event_auth.check(
-                RoomVersions.V1, event, auth_events,
+                RoomVersions.V1.identifier,
+                event,
+                auth_events,
                 do_sig_check=False,
                 do_size_check=False,
             )
diff --git a/synapse/storage/events_worker.py b/synapse/storage/events_worker.py
index 1716be529a..53c8dc3903 100644
--- a/synapse/storage/events_worker.py
+++ b/synapse/storage/events_worker.py
@@ -21,8 +21,9 @@ from canonicaljson import json
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventFormatVersions, EventTypes
+from synapse.api.constants import EventTypes
 from synapse.api.errors import NotFoundError
+from synapse.api.room_versions import EventFormatVersions
 from synapse.events import FrozenEvent, event_type_from_format_version  # noqa: F401
 # these are only included to make the type annotations work
 from synapse.events.snapshot import EventContext  # noqa: F401
diff --git a/tests/rest/client/v2_alpha/test_capabilities.py b/tests/rest/client/v2_alpha/test_capabilities.py
index d3d43970fb..bbfc77e829 100644
--- a/tests/rest/client/v2_alpha/test_capabilities.py
+++ b/tests/rest/client/v2_alpha/test_capabilities.py
@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from synapse.api.constants import DEFAULT_ROOM_VERSION, KNOWN_ROOM_VERSIONS
+from synapse.api.room_versions import DEFAULT_ROOM_VERSION, KNOWN_ROOM_VERSIONS
 from synapse.rest.client.v1 import admin, login
 from synapse.rest.client.v2_alpha import capabilities
 
@@ -52,7 +52,7 @@ class CapabilitiesTestCase(unittest.HomeserverTestCase):
         for room_version in capabilities['m.room_versions']['available'].keys():
             self.assertTrue(room_version in KNOWN_ROOM_VERSIONS, "" + room_version)
         self.assertEqual(
-            DEFAULT_ROOM_VERSION, capabilities['m.room_versions']['default']
+            DEFAULT_ROOM_VERSION.identifier, capabilities['m.room_versions']['default']
         )
 
     def test_get_change_password_capabilities(self):
diff --git a/tests/state/test_v2.py b/tests/state/test_v2.py
index 9a5c816927..f448b01326 100644
--- a/tests/state/test_v2.py
+++ b/tests/state/test_v2.py
@@ -19,7 +19,8 @@ from six.moves import zip
 
 import attr
 
-from synapse.api.constants import EventTypes, JoinRules, Membership, RoomVersions
+from synapse.api.constants import EventTypes, JoinRules, Membership
+from synapse.api.room_versions import RoomVersions
 from synapse.event_auth import auth_types_for_event
 from synapse.events import FrozenEvent
 from synapse.state.v2 import lexicographical_topological_sort, resolve_events_with_store
@@ -539,7 +540,7 @@ class StateTestCase(unittest.TestCase):
                 state_before = dict(state_at_event[prev_events[0]])
             else:
                 state_d = resolve_events_with_store(
-                    RoomVersions.V2,
+                    RoomVersions.V2.identifier,
                     [state_at_event[n] for n in prev_events],
                     event_map=event_map,
                     state_res_store=TestStateResolutionStore(event_map),
@@ -686,7 +687,7 @@ class SimpleParamStateTestCase(unittest.TestCase):
         # Test that we correctly handle passing `None` as the event_map
 
         state_d = resolve_events_with_store(
-            RoomVersions.V2,
+            RoomVersions.V2.identifier,
             [self.state_at_bob, self.state_at_charlie],
             event_map=None,
             state_res_store=TestStateResolutionStore(self.event_map),
diff --git a/tests/storage/test_redaction.py b/tests/storage/test_redaction.py
index 3957561b1e..0fc5019e9f 100644
--- a/tests/storage/test_redaction.py
+++ b/tests/storage/test_redaction.py
@@ -18,7 +18,8 @@ from mock import Mock
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventTypes, Membership, RoomVersions
+from synapse.api.constants import EventTypes, Membership
+from synapse.api.room_versions import RoomVersions
 from synapse.types import RoomID, UserID
 
 from tests import unittest
@@ -51,7 +52,7 @@ class RedactionTestCase(unittest.TestCase):
     ):
         content = {"membership": membership}
         content.update(extra_content)
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": EventTypes.Member,
@@ -74,7 +75,7 @@ class RedactionTestCase(unittest.TestCase):
     def inject_message(self, room, user, body):
         self.depth += 1
 
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": EventTypes.Message,
@@ -95,7 +96,7 @@ class RedactionTestCase(unittest.TestCase):
 
     @defer.inlineCallbacks
     def inject_redaction(self, room, event_id, user, reason):
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": EventTypes.Redaction,
diff --git a/tests/storage/test_roommember.py b/tests/storage/test_roommember.py
index 7fa2f4fd70..063387863e 100644
--- a/tests/storage/test_roommember.py
+++ b/tests/storage/test_roommember.py
@@ -18,7 +18,8 @@ from mock import Mock
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventTypes, Membership, RoomVersions
+from synapse.api.constants import EventTypes, Membership
+from synapse.api.room_versions import RoomVersions
 from synapse.types import RoomID, UserID
 
 from tests import unittest
@@ -49,7 +50,7 @@ class RoomMemberStoreTestCase(unittest.TestCase):
 
     @defer.inlineCallbacks
     def inject_room_member(self, room, user, membership, replaces_state=None):
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": EventTypes.Member,
diff --git a/tests/storage/test_state.py b/tests/storage/test_state.py
index 99cd3e09eb..78e260a7fa 100644
--- a/tests/storage/test_state.py
+++ b/tests/storage/test_state.py
@@ -17,7 +17,8 @@ import logging
 
 from twisted.internet import defer
 
-from synapse.api.constants import EventTypes, Membership, RoomVersions
+from synapse.api.constants import EventTypes, Membership
+from synapse.api.room_versions import RoomVersions
 from synapse.storage.state import StateFilter
 from synapse.types import RoomID, UserID
 
@@ -48,7 +49,7 @@ class StateStoreTestCase(tests.unittest.TestCase):
 
     @defer.inlineCallbacks
     def inject_state_event(self, room, sender, typ, state_key, content):
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": typ,
diff --git a/tests/test_event_auth.py b/tests/test_event_auth.py
index 7ee318e4e8..4c8f87e958 100644
--- a/tests/test_event_auth.py
+++ b/tests/test_event_auth.py
@@ -16,8 +16,8 @@
 import unittest
 
 from synapse import event_auth
-from synapse.api.constants import RoomVersions
 from synapse.api.errors import AuthError
+from synapse.api.room_versions import RoomVersions
 from synapse.events import FrozenEvent
 
 
@@ -37,7 +37,7 @@ class EventAuthTestCase(unittest.TestCase):
 
         # creator should be able to send state
         event_auth.check(
-            RoomVersions.V1, _random_state_event(creator), auth_events,
+            RoomVersions.V1.identifier, _random_state_event(creator), auth_events,
             do_sig_check=False,
         )
 
@@ -45,7 +45,7 @@ class EventAuthTestCase(unittest.TestCase):
         self.assertRaises(
             AuthError,
             event_auth.check,
-            RoomVersions.V1,
+            RoomVersions.V1.identifier,
             _random_state_event(joiner),
             auth_events,
             do_sig_check=False,
@@ -74,7 +74,7 @@ class EventAuthTestCase(unittest.TestCase):
         self.assertRaises(
             AuthError,
             event_auth.check,
-            RoomVersions.V1,
+            RoomVersions.V1.identifier,
             _random_state_event(pleb),
             auth_events,
             do_sig_check=False,
@@ -82,7 +82,7 @@ class EventAuthTestCase(unittest.TestCase):
 
         # king should be able to send state
         event_auth.check(
-            RoomVersions.V1, _random_state_event(king), auth_events,
+            RoomVersions.V1.identifier, _random_state_event(king), auth_events,
             do_sig_check=False,
         )
 
diff --git a/tests/test_state.py b/tests/test_state.py
index e20c33322a..03e4810c2e 100644
--- a/tests/test_state.py
+++ b/tests/test_state.py
@@ -18,7 +18,8 @@ from mock import Mock
 from twisted.internet import defer
 
 from synapse.api.auth import Auth
-from synapse.api.constants import EventTypes, Membership, RoomVersions
+from synapse.api.constants import EventTypes, Membership
+from synapse.api.room_versions import RoomVersions
 from synapse.events import FrozenEvent
 from synapse.state import StateHandler, StateResolutionHandler
 
@@ -118,7 +119,7 @@ class StateGroupStore(object):
         self._event_to_state_group[event_id] = state_group
 
     def get_room_version(self, room_id):
-        return RoomVersions.V1
+        return RoomVersions.V1.identifier
 
 
 class DictObj(dict):
diff --git a/tests/test_visibility.py b/tests/test_visibility.py
index 455db9f276..3bdb500514 100644
--- a/tests/test_visibility.py
+++ b/tests/test_visibility.py
@@ -17,7 +17,7 @@ import logging
 from twisted.internet import defer
 from twisted.internet.defer import succeed
 
-from synapse.api.constants import RoomVersions
+from synapse.api.room_versions import RoomVersions
 from synapse.events import FrozenEvent
 from synapse.visibility import filter_events_for_server
 
@@ -124,7 +124,7 @@ class FilterEventsForServerTestCase(tests.unittest.TestCase):
     @defer.inlineCallbacks
     def inject_visibility(self, user_id, visibility):
         content = {"history_visibility": visibility}
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": "m.room.history_visibility",
@@ -145,7 +145,7 @@ class FilterEventsForServerTestCase(tests.unittest.TestCase):
     def inject_room_member(self, user_id, membership="join", extra_content={}):
         content = {"membership": membership}
         content.update(extra_content)
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": "m.room.member",
@@ -167,7 +167,7 @@ class FilterEventsForServerTestCase(tests.unittest.TestCase):
     def inject_message(self, user_id, content=None):
         if content is None:
             content = {"body": "testytest", "msgtype": "m.text"}
-        builder = self.event_builder_factory.new(
+        builder = self.event_builder_factory.for_room_version(
             RoomVersions.V1,
             {
                 "type": "m.room.message",
diff --git a/tests/utils.py b/tests/utils.py
index 615b9f8cca..cb75514851 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -27,8 +27,9 @@ from six.moves.urllib import parse as urlparse
 
 from twisted.internet import defer, reactor
 
-from synapse.api.constants import EventTypes, RoomVersions
+from synapse.api.constants import EventTypes
 from synapse.api.errors import CodeMessageException, cs_error
+from synapse.api.room_versions import RoomVersions
 from synapse.config.homeserver import HomeServerConfig
 from synapse.federation.transport import server as federation_server
 from synapse.http.server import HttpServer
@@ -671,7 +672,7 @@ def create_room(hs, room_id, creator_id):
     event_builder_factory = hs.get_event_builder_factory()
     event_creation_handler = hs.get_event_creation_handler()
 
-    builder = event_builder_factory.new(
+    builder = event_builder_factory.for_room_version(
         RoomVersions.V1,
         {
             "type": EventTypes.Create,