Add MSC2716 to room capabilities

Spawned from https://github.com/matrix-org/matrix-js-sdk/pull/2299#discussion_r852893524

synapse/api/room_versions.py

@@ -313,3 +313,28 @@ MSC3244_CAPABILITIES = {
         ),
     )
 }
+
+MSC2716_CAPABILITIES = {
+    cap.identifier: {
+        "preferred": cap.preferred_version.identifier
+        if cap.preferred_version is not None
+        else None,
+        "support": [
+            v.identifier
+            for v in KNOWN_ROOM_VERSIONS.values()
+            if cap.support_check_lambda(v)
+        ],
+    }
+    for cap in (
+        RoomVersionCapability(
+            "historical",
+            RoomVersions.MSC2716v3,
+            lambda room_version: room_version.msc2716_historical,
+        ),
+        RoomVersionCapability(
+            "redactions",
+            RoomVersions.MSC2716v3,
+            lambda room_version: room_version.msc2716_redactions,
+        ),
+    )
+}

synapse/rest/client/capabilities.py

@@ -15,7 +15,11 @@ import logging
 from http import HTTPStatus
 from typing import TYPE_CHECKING, Tuple
 
-from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, MSC3244_CAPABILITIES
+from synapse.api.room_versions import (
+    KNOWN_ROOM_VERSIONS,
+    MSC3244_CAPABILITIES,
+    MSC2716_CAPABILITIES,
+)
 from synapse.http.server import HttpServer
 from synapse.http.servlet import RestServlet
 from synapse.http.site import SynapseRequest
@@ -72,6 +76,12 @@ class CapabilitiesRestServlet(RestServlet):
                 "org.matrix.msc3244.room_capabilities"
             ] = MSC3244_CAPABILITIES
 
+        logger.info("ewffewaafewafew")
+        if self.config.experimental.msc2716_enabled:
+            response["capabilities"]["m.room_versions"][
+                "org.matrix.msc2716.room_capabilities"
+            ] = MSC2716_CAPABILITIES
+
         if self.config.experimental.msc3720_enabled:
             response["capabilities"]["org.matrix.msc3720.account_status"] = {
                 "enabled": True,

tests/rest/client/test_capabilities.py

@@ -187,3 +187,43 @@ class CapabilitiesTestCase(unittest.HomeserverTestCase):
             self.assertGreater(len(details["support"]), 0)
             for room_version in details["support"]:
                 self.assertTrue(room_version in KNOWN_ROOM_VERSIONS, str(room_version))
+
+    def test_get_does_not_include_msc2716_fields_when_disabled(self) -> None:
+        access_token = self.get_success(
+            self.auth_handler.create_access_token_for_user_id(
+                self.user, device_id=None, valid_until_ms=None
+            )
+        )
+
+        channel = self.make_request("GET", self.url, access_token=access_token)
+        capabilities = channel.json_body["capabilities"]
+
+        self.assertEqual(channel.code, 200)
+        self.assertNotIn(
+            "org.matrix.msc2716.room_capabilities", capabilities["m.room_versions"]
+        )
+
+    @override_config({"experimental_features": {"msc2716_enabled": True}})
+    def test_get_does_include_msc2716_fields_when_enabled(self) -> None:
+        access_token = self.get_success(
+            self.auth_handler.create_access_token_for_user_id(
+                self.user, device_id=None, valid_until_ms=None
+            )
+        )
+
+        channel = self.make_request("GET", self.url, access_token=access_token)
+        capabilities = channel.json_body["capabilities"]
+
+        self.assertEqual(channel.code, 200)
+        for details in capabilities["m.room_versions"][
+            "org.matrix.msc2716.room_capabilities"
+        ].values():
+            if details["preferred"] is not None:
+                self.assertTrue(
+                    details["preferred"] in KNOWN_ROOM_VERSIONS,
+                    str(details["preferred"]),
+                )
+
+            self.assertGreater(len(details["support"]), 0)
+            for room_version in details["support"]:
+                self.assertTrue(room_version in KNOWN_ROOM_VERSIONS, str(room_version))