!fixup remove the recursion_limit increase.

crates/matrix-sdk-common/src/deserialized_responses.rs

@@ -306,6 +306,25 @@ pub struct EncryptionInfo {
 /// Previously, this differed from [`TimelineEvent`] by wrapping an
 /// [`AnySyncTimelineEvent`] instead of an [`AnyTimelineEvent`], but nowadays
 /// they are essentially identical, and one of them should probably be removed.
+//
+// 🚨 Note about this type, please read! 🚨
+//
+// `SyncTimelineEvent` is heavily used across the SDK crates. In some cases, we
+// are reaching a [`recursion_limit`] when the compiler is trying to figure out
+// if `SyncTimelineEvent` implements `Sync` when it's embedded in other types.
+//
+// We want to help the compiler so that one doesn't need to increase the
+// `recursion_limit`. We stop the recursive check by (un)safely implement `Sync`
+// and `Send` on `SyncTimelineEvent` directly. However, before doing that, we
+// need to ensure that every field of `SyncTimelineEvent` implements `Sync` and
+// `Send` too. That's why we have `assert_sync_and_send` in a const expression
+// so that it is checked at compile-time. If these checks pass, we can (un)safely
+// implement `Sync` and `Send` for `SyncTimelineEvent`.
+//
+// If a field must be added to this type, please update the calls to
+// `assert_sync_and_send`.
+//
+// [`recursion_limit`]: https://doc.rust-lang.org/reference/attributes/limits.html#the-recursion_limit-attribute
 #[derive(Clone, Debug, Serialize)]
 pub struct SyncTimelineEvent {
     /// The event itself, together with any information on decryption.
@@ -316,6 +335,21 @@ pub struct SyncTimelineEvent {
     pub push_actions: Vec<Action>,
 }
 
+const _: fn() = || {
+    fn assert_sync_and_send<T: ?Sized + Sync + Send>() {}
+
+    // `SyncTimelineEvent::kind` is of type `TimelineEventKind`.
+    assert_sync_and_send::<TimelineEventKind>();
+
+    // `SyncTimelineEvent::push_actions` is of type `Vec<Action>`.
+    assert_sync_and_send::<Vec<Action>>();
+};
+
+// All fields of `SyncTimelineEvent` implements `Sync` and `Send`: we can safely
+// implement `Sync` and `Send` for `SyncTimelineEvent` directly.
+unsafe impl Sync for SyncTimelineEvent {}
+unsafe impl Send for SyncTimelineEvent {}
+
 impl SyncTimelineEvent {
     /// Create a new `SyncTimelineEvent` from the given raw event.
     ///

crates/matrix-sdk-ui/tests/integration/main.rs

@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![recursion_limit = "256"]
-
 use itertools::Itertools as _;
 use matrix_sdk::deserialized_responses::TimelineEvent;
 use ruma::{events::AnyStateEvent, serde::Raw, EventId, RoomId};