Stabilize set_displayname() in module API (matrix-org#14628)

changelog.d/14629.feature

@@ -0,0 +1 @@
+Adds a `set_displayname()` method to the module API for setting a user's display name.

synapse/module_api/__init__.py

@@ -1585,6 +1585,33 @@ async def create_room(
 
         return room_id_and_alias["room_id"], room_id_and_alias.get("room_alias", None)
 
+    async def set_displayname(
+        self,
+        user_id: UserID,
+        new_displayname: str,
+        deactivation: bool = False,
+    ) -> None:
+        """Sets a user's display name.
+
+        Added in Synapse v1.75.0.
+
+        Args:
+            user_id:
+                The user whose display name is to be changed.
+            new_displayname:
+                The new display name to give the user.
+            deactivation:
+                Whether this change was made while deactivating the user.
+        """
+        requester = create_requester(user_id)
+        await self._hs.get_profile_handler().set_displayname(
+            target_user=user_id,
+            requester=requester,
+            new_displayname=new_displayname,
+            by_admin=True,
+            deactivation=deactivation,
+        )
+
 
 class PublicRoomListManager:
     """Contains methods for adding to, removing from and querying whether a room

tests/module_api/test_api.py

@@ -110,6 +110,24 @@ def test_can_set_admin(self):
         self.assertEqual(found_user.user_id.to_string(), user_id)
         self.assertIdentical(found_user.is_admin, True)
 
+    def test_can_set_displayname(self):
+        localpart = "alice_wants_a_new_displayname"
+        user_id = self.register_user(localpart, "1234", displayname="Alice", admin=False)
+        found_userinfo = self.get_success(
+            self.module_api.get_userinfo_by_id(user_id)
+        )
+
+        self.get_success(
+            self.module_api.set_displayname(
+                found_userinfo.user_id, "Bob", deactivation=False
+            )
+        )
+        found_profile = self.get_success(
+            self.module_api.get_profile_for_user(localpart)
+        )
+
+        self.assertEqual(found_profile.display_name, "Bob")
+
     def test_get_userinfo_by_id(self):
         user_id = self.register_user("alice", "1234")
         found_user = self.get_success(self.module_api.get_userinfo_by_id(user_id))