Finish up work to allow per-user feature flags (#17392)

Follows on from @H-Shay's great work at
https://github.com/matrix-org/synapse/pull/15344 and MSC4026.

Also enables its use for MSC3881, mainly as an easy but concrete example
of how to use it.

1 files changed, 9 insertions, 2 deletions

diff --git a/synapse/rest/admin/experimental_features.py b/synapse/rest/admin/experimental_features.py

index c5a00c490c..c1559c92f7 100644
--- a/synapse/rest/admin/experimental_features.py
+++ b/synapse/rest/admin/experimental_features.py
@@ -31,7 +31,9 @@ from synapse.rest.admin import admin_patterns, assert_requester_is_admin
 from synapse.types import JsonDict, UserID
 
 if TYPE_CHECKING:
-    from synapse.server import HomeServer
+    from typing_extensions import assert_never
+
+    from synapse.server import HomeServer, HomeServerConfig
 
 
 class ExperimentalFeature(str, Enum):
@@ -39,9 +41,14 @@ class ExperimentalFeature(str, Enum):
     Currently supported per-user features
     """
 
-    MSC3026 = "msc3026"
     MSC3881 = "msc3881"
 
+    def is_globally_enabled(self, config: "HomeServerConfig") -> bool:
+        if self is ExperimentalFeature.MSC3881:
+            return config.experimental.msc3881_enabled
+
+        assert_never(self)
+
 
 class ExperimentalFeaturesRestServlet(RestServlet):
     """