SS: Implement `$ME` support (#17469)

`$ME` can be used as a substitute for the requester's user ID.

1 files changed, 5 insertions, 1 deletions

diff --git a/synapse/handlers/sliding_sync.py b/synapse/handlers/sliding_sync.py
index 423f0329d6..c362afa6e2 100644
--- a/synapse/handlers/sliding_sync.py
+++ b/synapse/handlers/sliding_sync.py
@@ -329,6 +329,9 @@ class StateValues:
     # `sender` in the timeline). We only give special meaning to this value when it's a
     # `state_key`.
     LAZY: Final = "$LAZY"
+    # Subsitute with the requester's user ID. Typically used by clients to get
+    # the user's membership.
+    ME: Final = "$ME"
 
 
 class SlidingSyncHandler:
@@ -504,7 +507,6 @@ class SlidingSyncHandler:
                 # Also see `StateFilter.must_await_full_state(...)` for comparison
                 lazy_loading = (
                     membership_state_keys is not None
-                    and len(membership_state_keys) == 1
                     and StateValues.LAZY in membership_state_keys
                 )
 
@@ -1662,6 +1664,8 @@ class SlidingSyncHandler:
 
                             # FIXME: We probably also care about invite, ban, kick, targets, etc
                             # but the spec only mentions "senders".
+                        elif state_key == StateValues.ME:
+                            required_state_types.append((state_type, user.to_string()))
                         else:
                             required_state_types.append((state_type, state_key))