sdk-common: hack to avoid over-recursion when evaluating Send/Sync bo…

…unds in rustc

See
#3749 (comment)
for the gory details.

crates/matrix-sdk-common/Cargo.toml

@@ -19,6 +19,10 @@ targets = ["x86_64-unknown-linux-gnu", "wasm32-unknown-unknown"]
 js = ["wasm-bindgen-futures"]
 uniffi = ["dep:uniffi"]
 
+# Used internally to make sure that some types are actually really send and sync.
+# See also https://github.com/matrix-org/matrix-rust-sdk/pull/3749#issuecomment-2312939823.
+test-send-sync = []
+
 [dependencies]
 async-trait = { workspace = true }
 futures-core = { workspace = true }

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

@@ -296,6 +296,23 @@ pub struct SyncTimelineEvent {
     pub unsigned_encryption_info: Option<BTreeMap<UnsignedEventLocation, UnsignedDecryptionResult>>,
 }
 
+/// See https://github.com/matrix-org/matrix-rust-sdk/pull/3749#issuecomment-2312939823.
+#[cfg(not(feature = "test-send-sync"))]
+unsafe impl Send for SyncTimelineEvent {}
+
+/// See https://github.com/matrix-org/matrix-rust-sdk/pull/3749#issuecomment-2312939823.
+#[cfg(not(feature = "test-send-sync"))]
+unsafe impl Sync for SyncTimelineEvent {}
+
+#[cfg(feature = "test-send-sync")]
+#[test]
+/// See https://github.com/matrix-org/matrix-rust-sdk/pull/3749#issuecomment-2312939823.
+fn test_send_sync_for_sync_timeline_event() {
+    fn assert_send_sync<T: Send + Sync>() {}
+
+    assert_send_sync::<SyncTimelineEvent>();
+}
+
 impl SyncTimelineEvent {
     /// Create a new `SyncTimelineEvent` from the given raw event.
     ///

xtask/src/ci.rs

@@ -294,7 +294,7 @@ fn run_wasm_checks(cmd: Option<WasmFeatureSet>) -> Result<()> {
             "-p matrix-sdk --no-default-features --features js,rustls-tls",
         ),
         (WasmFeatureSet::MatrixSdkBase, "-p matrix-sdk-base --features js"),
-        (WasmFeatureSet::MatrixSdkCommon, "-p matrix-sdk-common --features js"),
+        (WasmFeatureSet::MatrixSdkCommon, "-p matrix-sdk-common --features js,test-send-sync"),
         (
             WasmFeatureSet::MatrixSdkIndexeddbStoresNoCrypto,
             "-p matrix-sdk --no-default-features --features js,indexeddb,rustls-tls",