Change default room version to 10. Implements MSC3904 (#14111)

* Change Documentation to have v10 as default room version

* Change Default Room version to 10

* Add changelog entry for default room version swap

* Add changelog entry for v10 default room version in docs

* Clarify doc changelog entry

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>

* Improve Documentation changes.

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>

* Update Changelog entry to have correct format

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>

* Update Spec Version to 1.5

* Only need 1 changelog.

* Fix test.

* Update "Changed in" line

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>
Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>
Co-authored-by: Patrick Cloke <patrickc@matrix.org>

4 files changed, 14 insertions, 5 deletions

diff --git a/changelog.d/14111.feature b/changelog.d/14111.feature
new file mode 100644
index 0000000000..0a794701a7
--- /dev/null
+++ b/changelog.d/14111.feature
@@ -0,0 +1 @@
+Update the default room version to [v10](https://spec.matrix.org/v1.5/rooms/v10/) ([MSC 3904](https://github.com/matrix-org/matrix-spec-proposals/pull/3904)). Contributed by @FSG-Cat.
\ No newline at end of file
diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md
index 3481e866f7..2883f76a26 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -295,7 +295,9 @@ Known room versions are listed [here](https://spec.matrix.org/latest/rooms/#comp
 For example, for room version 1, `default_room_version` should be set
 to "1".
 
-Currently defaults to "9".
+Currently defaults to ["10"](https://spec.matrix.org/v1.5/rooms/v10/).
+
+_Changed in Synapse 1.76:_ the default version room version was increased from [9](https://spec.matrix.org/v1.5/rooms/v9/) to [10](https://spec.matrix.org/v1.5/rooms/v10/).
 
 Example configuration:
 ```yaml
diff --git a/synapse/config/server.py b/synapse/config/server.py
index ec46ca63ad..80bcfa4080 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -151,7 +151,7 @@ DEFAULT_IP_RANGE_BLACKLIST = [
     "fec0::/10",
 ]
 
-DEFAULT_ROOM_VERSION = "9"
+DEFAULT_ROOM_VERSION = "10"
 
 ROOM_COMPLEXITY_TOO_GREAT = (
     "Your homeserver is unable to join rooms this large or complex. "
diff --git a/tests/rest/client/test_upgrade_room.py b/tests/rest/client/test_upgrade_room.py
index 5e7bf97482..5ec343dd7f 100644
--- a/tests/rest/client/test_upgrade_room.py
+++ b/tests/rest/client/test_upgrade_room.py
@@ -199,9 +199,15 @@ class UpgradeRoomTest(unittest.HomeserverTestCase):
 
     def test_stringy_power_levels(self) -> None:
         """The room upgrade converts stringy power levels to proper integers."""
+        # Create a room on room version < 10.
+        room_id = self.helper.create_room_as(
+            self.creator, tok=self.creator_token, room_version="9"
+        )
+        self.helper.join(room_id, self.other, tok=self.other_token)
+
         # Retrieve the room's current power levels.
         power_levels = self.helper.get_state(
-            self.room_id,
+            room_id,
             "m.room.power_levels",
             tok=self.creator_token,
         )
@@ -217,14 +223,14 @@ class UpgradeRoomTest(unittest.HomeserverTestCase):
             # conscience, we ought to ensure it's upgrading from a sufficiently old
             # version of room.
             self.helper.send_state(
-                self.room_id,
+                room_id,
                 "m.room.power_levels",
                 body=power_levels,
                 tok=self.creator_token,
             )
 
         # Upgrade the room. Check the homeserver reports success.
-        channel = self._upgrade_room()
+        channel = self._upgrade_room(room_id=room_id)
         self.assertEqual(200, channel.code, channel.result)
 
         # Extract the new room ID.