clippy: disallow useless asyncs (#3513)

Using async when not required will increase compile times, and propagate async-ness to the callers, transitively.

See also the [lint description](https://rust-lang.github.io/rust-clippy/master/#/unused_async).

Since we only had a few false positives, I've enabled it by default.

.cargo/config.toml

@@ -38,6 +38,7 @@ rustflags = [
     "-Wclippy::nonstandard_macro_braces",
     "-Wclippy::str_to_string",
     "-Wclippy::todo",
+    "-Wclippy::unused_async",
 ]
 
 [target.'cfg(target_arch = "wasm32")']

bindings/matrix-sdk-crypto-ffi/src/machine.rs

@@ -1158,8 +1158,7 @@ impl OlmMachine {
         let methods = methods.into_iter().map(VerificationMethod::from).collect();
 
         Ok(if let Some(identity) = identity.and_then(|i| i.other()) {
-            let content =
-                self.runtime.block_on(identity.verification_request_content(Some(methods)));
+            let content = identity.verification_request_content(Some(methods));
             Some(serde_json::to_string(&content)?)
         } else {
             None
@@ -1202,11 +1201,7 @@ impl OlmMachine {
         let methods = methods.into_iter().map(VerificationMethod::from).collect();
 
         Ok(if let Some(identity) = identity.and_then(|i| i.other()) {
-            let request = self.runtime.block_on(identity.request_verification(
-                &room_id,
-                &event_id,
-                Some(methods),
-            ));
+            let request = identity.request_verification(&room_id, &event_id, Some(methods));
 
             Some(
                 VerificationRequest { inner: request, runtime: self.runtime.handle().to_owned() }
@@ -1243,8 +1238,7 @@ impl OlmMachine {
             if let Some(device) =
                 self.runtime.block_on(self.inner.get_device(&user_id, device_id, None))?
             {
-                let (verification, request) =
-                    self.runtime.block_on(device.request_verification_with_methods(methods));
+                let (verification, request) = device.request_verification_with_methods(methods);
 
                 Some(RequestVerificationResult {
                     verification: VerificationRequest {

bindings/matrix-sdk-ffi/src/authentication_service.rs

@@ -456,7 +456,7 @@ impl AuthenticationService {
 
         let oidc_metadata: VerifiedClientMetadata = configuration.try_into()?;
 
-        if self.load_client_registration(oidc, issuer.clone(), oidc_metadata.clone()).await {
+        if self.load_client_registration(oidc, issuer.clone(), oidc_metadata.clone()) {
             tracing::info!("OIDC configuration loaded from disk.");
             return Ok(());
         }
@@ -472,14 +472,14 @@ impl AuthenticationService {
         oidc.restore_registered_client(issuer, oidc_metadata, credentials);
 
         tracing::info!("Persisting OIDC registration data.");
-        self.store_client_registration(oidc).await?;
+        self.store_client_registration(oidc)?;
 
         Ok(())
     }
 
     /// Stores the current OIDC dynamic client registration so it can be re-used
     /// if we ever log in via the same issuer again.
-    async fn store_client_registration(&self, oidc: &Oidc) -> Result<(), AuthenticationError> {
+    fn store_client_registration(&self, oidc: &Oidc) -> Result<(), AuthenticationError> {
         let issuer = Url::parse(oidc.issuer().ok_or(AuthenticationError::OidcNotSupported)?)
             .map_err(|_| AuthenticationError::OidcError {
                 message: String::from("Failed to parse issuer URL."),
@@ -508,7 +508,7 @@ impl AuthenticationService {
 
     /// Attempts to load an existing OIDC dynamic client registration for the
     /// currently configured issuer.
-    async fn load_client_registration(
+    fn load_client_registration(
         &self,
         oidc: &Oidc,
         issuer: String,

bindings/matrix-sdk-ffi/src/client.rs

@@ -242,9 +242,7 @@ impl Client {
                     let session_delegate = session_delegate.clone();
                     Box::new(move |client| {
                         let session_delegate = session_delegate.clone();
-                        Box::pin(
-                            async move { Ok(Self::save_session(session_delegate, client).await?) },
-                        )
+                        Ok(Self::save_session(session_delegate, client)?)
                     })
                 },
             )?;
@@ -415,8 +413,8 @@ impl Client {
         })
     }
 
-    pub async fn session(&self) -> Result<Session, ClientError> {
-        Self::session_inner((*self.inner).clone()).await
+    pub fn session(&self) -> Result<Session, ClientError> {
+        Self::session_inner((*self.inner).clone())
     }
 
     pub async fn account_url(
@@ -968,7 +966,7 @@ impl Client {
         }
     }
 
-    async fn session_inner(client: matrix_sdk::Client) -> Result<Session, ClientError> {
+    fn session_inner(client: matrix_sdk::Client) -> Result<Session, ClientError> {
         let auth_api = client.auth_api().context("Missing authentication API")?;
 
         let homeserver_url = client.homeserver().into();
@@ -977,11 +975,11 @@ impl Client {
         Session::new(auth_api, homeserver_url, sliding_sync_proxy)
     }
 
-    async fn save_session(
+    fn save_session(
         session_delegate: Arc<dyn ClientSessionDelegate>,
         client: matrix_sdk::Client,
     ) -> anyhow::Result<()> {
-        let session = Self::session_inner(client).await?;
+        let session = Self::session_inner(client)?;
         session_delegate.save_session_in_keychain(session);
         Ok(())
     }

bindings/matrix-sdk-ffi/src/room_list.rs

@@ -510,9 +510,10 @@ impl RoomListItem {
         Ok(RoomInfo::new(self.inner.inner_room(), latest_event).await?)
     }
 
-    /// Building a `Room`. If its internal timeline hasn't been initialized
-    /// it'll fail.
-    async fn full_room(&self) -> Result<Arc<Room>, RoomListError> {
+    /// Build a full `Room` FFI object, filling its associated timeline.
+    ///
+    /// If its internal timeline hasn't been initialized, it'll fail.
+    fn full_room(&self) -> Result<Arc<Room>, RoomListError> {
         if let Some(timeline) = self.inner.timeline() {
             Ok(Arc::new(Room::with_timeline(
                 self.inner.inner_room().clone(),

crates/matrix-sdk-base/src/client.rs

@@ -418,7 +418,6 @@ impl BaseClient {
                             room_info,
                             changes,
                         )
-                        .await;
                     } else {
                         push_context = self.get_push_room_context(room, room_info, changes).await?;
                     }
@@ -1409,7 +1408,7 @@ impl BaseClient {
     /// Update the push context for the given room.
     ///
     /// Updates the context data from `changes` or `room_info`.
-    pub async fn update_push_room_context(
+    pub fn update_push_room_context(
         &self,
         push_rules: &mut PushConditionRoomCtx,
         user_id: &UserId,