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).

3 files changed, 18 insertions, 13 deletions

diff --git a/changelog.d/13920.feature b/changelog.d/13920.feature
new file mode 100644
index 0000000000..aee702bcd2
--- /dev/null
+++ b/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).
diff --git a/synapse/rest/client/relations.py b/synapse/rest/client/relations.py
index ce97080013..205c556f64 100644
--- a/synapse/rest/client/relations.py
+++ b/synapse/rest/client/relations.py
@@ -56,15 +56,21 @@ class RelationPaginationServlet(RestServlet):
         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")
 
diff --git a/tests/rest/client/test_relations.py b/tests/rest/client/test_relations.py
index d33e34d829..fef3b72d76 100644
--- a/tests/rest/client/test_relations.py
+++ b/tests/rest/client/test_relations.py
@@ -728,7 +728,6 @@ class RelationsTestCase(BaseRelationsTestCase):
 
 
 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 @@ class RelationPaginationTestCase(BaseRelationsTestCase):
         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 @@ class RelationPaginationTestCase(BaseRelationsTestCase):
             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 @@ class RelationPaginationTestCase(BaseRelationsTestCase):
 
             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)