Support the stable dir parameter for /relations. (#13920)

Since MSC3715 has passed FCP, the stable parameter can be used.

This currently falls back to the unstable parameter if the stable
parameter is not provided (and MSC3715 support is enabled in
the configuration).

changelog.d/13920.feature

@@ -0,0 +1 @@
+Support a `dir` parameter on the `/relations` endpoint per [MSC3715](https://github.com/matrix-org/matrix-doc/pull/3715).

synapse/rest/client/relations.py

@@ -56,15 +56,21 @@ async def on_GET(
         requester = await self.auth.get_user_by_req(request, allow_guest=True)
 
         limit = parse_integer(request, "limit", default=5)
-        if self._msc3715_enabled:
-            direction = parse_string(
-                request,
-                "org.matrix.msc3715.dir",
-                default="b",
-                allowed_values=["f", "b"],
-            )
-        else:
-            direction = "b"
+        # Fetch the direction parameter, if provided.
+        #
+        # TODO Use PaginationConfig.from_request when the unstable parameter is
+        #      no longer needed.
+        direction = parse_string(request, "dir", allowed_values=["f", "b"])
+        if direction is None:
+            if self._msc3715_enabled:
+                direction = parse_string(
+                    request,
+                    "org.matrix.msc3715.dir",
+                    default="b",
+                    allowed_values=["f", "b"],
+                )
+            else:
+                direction = "b"
         from_token_str = parse_string(request, "from")
         to_token_str = parse_string(request, "to")
 

tests/rest/client/test_relations.py

@@ -728,7 +728,6 @@ def test_background_update(self) -> None:
 
 
 class RelationPaginationTestCase(BaseRelationsTestCase):
-    @unittest.override_config({"experimental_features": {"msc3715_enabled": True}})
     def test_basic_paginate_relations(self) -> None:
         """Tests that calling pagination API correctly the latest relations."""
         channel = self._send_relation(RelationTypes.ANNOTATION, "m.reaction", "a")
@@ -771,7 +770,7 @@ def test_basic_paginate_relations(self) -> None:
         channel = self.make_request(
             "GET",
             f"/_matrix/client/v1/rooms/{self.room}/relations"
-            f"/{self.parent_id}?limit=1&org.matrix.msc3715.dir=f",
+            f"/{self.parent_id}?limit=1&dir=f",
             access_token=self.user_token,
         )
         self.assertEqual(200, channel.code, channel.json_body)
@@ -788,7 +787,6 @@ def test_basic_paginate_relations(self) -> None:
             channel.json_body["chunk"][0],
         )
 
-    @unittest.override_config({"experimental_features": {"msc3715_enabled": True}})
     def test_repeated_paginate_relations(self) -> None:
         """Test that if we paginate using a limit and tokens then we get the
         expected events.
@@ -838,7 +836,7 @@ def test_repeated_paginate_relations(self) -> None:
 
             channel = self.make_request(
                 "GET",
-                f"/_matrix/client/v1/rooms/{self.room}/relations/{self.parent_id}?org.matrix.msc3715.dir=f&limit=3{from_token}",
+                f"/_matrix/client/v1/rooms/{self.room}/relations/{self.parent_id}?dir=f&limit=3{from_token}",
                 access_token=self.user_token,
             )
             self.assertEqual(200, channel.code, channel.json_body)