Use #[expect], lint reasons

Cargo.toml

@@ -19,6 +19,8 @@ unused_qualifications = "warn"
 pedantic = { level = "warn", priority = -1 }
 
 # Lints. Keep alphabetically sorted
+allow_attributes = "warn"
+allow_attributes_without_reason = "warn"
 as_conversions = "warn"
 assertions_on_result_states = "warn"
 dbg_macro = "warn"

src/api/client_server/account.rs

@@ -85,7 +85,7 @@ pub(crate) async fn get_register_available_route(
 /// - Creates a new account and populates it with default account data
 /// - If `inhibit_login` is false: Creates a device and returns `device_id` and
 ///   `access_token`
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn register_route(
     body: Ar<register::v3::Request>,
 ) -> Result<Ra<register::v3::Response>> {

src/api/client_server/context.rs

@@ -17,7 +17,7 @@ use crate::{services, Ar, Error, Ra, Result};
 ///
 /// - Only works if the user is joined (TODO: always allow, but only show events
 ///   if the user was joined, depending on `history_visibility`)
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn get_context_route(
     body: Ar<get_context::v3::Request>,
 ) -> Result<Ra<get_context::v3::Response>> {

src/api/client_server/directory.rs

@@ -137,7 +137,7 @@ pub(crate) async fn get_room_visibility_route(
     }))
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn get_public_rooms_filtered_helper(
     server: Option<&ServerName>,
     limit: Option<UInt>,
@@ -267,7 +267,6 @@ pub(crate) async fn get_public_rooms_filtered_helper(
     })
 }
 
-#[allow(clippy::too_many_lines)]
 #[tracing::instrument]
 fn room_id_to_chunk(room_id: ruma::OwnedRoomId) -> Result<PublicRoomsChunk> {
     let canonical_alias = services()

src/api/client_server/keys.rs

@@ -284,7 +284,7 @@ pub(crate) async fn get_key_changes_route(
     }))
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn get_keys_helper<F: Fn(&UserId) -> bool>(
     sender_user: Option<&UserId>,
     device_keys_input: &BTreeMap<OwnedUserId, Vec<OwnedDeviceId>>,

src/api/client_server/media.rs

@@ -124,7 +124,7 @@ fn set_header_or_panic(
 /// # `GET /_matrix/media/r0/config`
 ///
 /// Returns max upload size.
-#[allow(deprecated)] // unauthenticated media
+#[expect(deprecated, reason = "legacy media APIs")]
 pub(crate) async fn get_media_config_legacy_route(
     _body: Ar<legacy_media::get_media_config::v3::Request>,
 ) -> Result<Ra<legacy_media::get_media_config::v3::Response>> {
@@ -196,7 +196,7 @@ impl From<bool> for AllowRemote {
 }
 
 struct RemoteResponse {
-    #[allow(unused)]
+    #[expect(unused, reason = "placeholder for future spec changes")]
     metadata: authenticated_media_fed::ContentMetadata,
     content: authenticated_media_fed::Content,
 }
@@ -290,7 +290,7 @@ async fn get_remote_content_via_federation_api(
     })
 }
 
-#[allow(deprecated)] // unauthenticated media
+#[expect(deprecated, reason = "legacy media APIs")]
 #[tracing::instrument(skip_all)]
 async fn get_remote_content_via_legacy_api(
     mxc: &MxcData<'_>,
@@ -365,7 +365,7 @@ pub(crate) async fn get_remote_content(
 /// Load media from our server or over federation.
 ///
 /// - Only allows federation if `allow_remote` is true
-#[allow(deprecated)] // unauthenticated media
+#[expect(deprecated, reason = "legacy media APIs")]
 pub(crate) async fn get_content_legacy_route(
     body: Ar<legacy_media::get_content::v3::Request>,
 ) -> Result<axum::response::Response> {
@@ -487,7 +487,7 @@ async fn get_content_route_ruma(
 /// Load media from our server or over federation, permitting desired filename.
 ///
 /// - Only allows federation if `allow_remote` is true
-#[allow(deprecated)] // unauthenticated media
+#[expect(deprecated, reason = "legacy media APIs")]
 pub(crate) async fn get_content_as_filename_legacy_route(
     body: Ar<legacy_media::get_content_as_filename::v3::Request>,
 ) -> Result<axum::response::Response> {
@@ -632,7 +632,7 @@ fn fix_thumbnail_headers(r: &mut axum::response::Response) {
 /// Load media thumbnail from our server or over federation.
 ///
 /// - Only allows federation if `allow_remote` is true
-#[allow(deprecated)] // unauthenticated media
+#[expect(deprecated, reason = "legacy media APIs")]
 pub(crate) async fn get_content_thumbnail_legacy_route(
     body: Ar<legacy_media::get_content_thumbnail::v3::Request>,
 ) -> Result<axum::response::Response> {
@@ -741,7 +741,7 @@ async fn get_remote_thumbnail_via_federation_api(
     })
 }
 
-#[allow(deprecated)] // unauthenticated media
+#[expect(deprecated, reason = "legacy media APIs")]
 #[tracing::instrument(skip_all)]
 async fn get_remote_thumbnail_via_legacy_api(
     server_name: &ruma::ServerName,

src/api/client_server/membership.rs

@@ -499,7 +499,6 @@ pub(crate) async fn joined_members_route(
     }))
 }
 
-#[allow(clippy::too_many_lines)]
 #[tracing::instrument(skip(reason, _third_party_signed))]
 async fn join_room_by_id_helper(
     sender_user: Option<&UserId>,
@@ -1265,7 +1264,7 @@ async fn validate_and_add_event_id(
     Ok((event_id, value))
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn invite_helper(
     sender_user: &UserId,
     user_id: &UserId,
@@ -1571,7 +1570,7 @@ pub(crate) async fn leave_room(
     Ok(())
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 async fn remote_leave_room(user_id: &UserId, room_id: &RoomId) -> Result<()> {
     let mut make_leave_response_and_server = Err(Error::BadServerResponse(
         "No server available to assist in leaving.",

src/api/client_server/message.rs

@@ -118,7 +118,7 @@ pub(crate) async fn send_message_event_route(
 ///
 /// - Only works if the user is joined (TODO: always allow, but only show events
 ///   where the user was joined, depending on `history_visibility`)
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn get_message_events_route(
     body: Ar<get_message_events::v3::Request>,
 ) -> Result<Ra<get_message_events::v3::Response>> {

src/api/client_server/room.rs

@@ -50,7 +50,7 @@ use crate::{
 /// - Send events listed in initial state
 /// - Send events implied by `name` and `topic`
 /// - Send invite events
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn create_room_route(
     body: Ar<create_room::v3::Request>,
 ) -> Result<Ra<create_room::v3::Response>> {
@@ -570,7 +570,7 @@ pub(crate) async fn get_room_aliases_route(
 /// - Transfers some state events
 /// - Moves local aliases
 /// - Modifies old room power levels to prevent users from speaking
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn upgrade_room_route(
     body: Ar<upgrade_room::v3::Request>,
 ) -> Result<Ra<upgrade_room::v3::Response>> {

src/api/client_server/search.rs

@@ -22,7 +22,7 @@ use crate::{services, Ar, Error, Ra, Result};
 ///
 /// - Only works if the user is currently joined to the room (TODO: Respect
 ///   history visibility)
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn search_events_route(
     body: Ar<search_events::v3::Request>,
 ) -> Result<Ra<search_events::v3::Response>> {

src/api/client_server/session.rs

@@ -51,11 +51,8 @@ pub(crate) async fn get_login_types_route(
 ///
 /// Note: You can use [`GET /_matrix/client/r0/login`](get_login_types_route) to
 /// see supported login types.
-#[allow(
-    // To allow deprecated login methods
-    deprecated,
-    clippy::too_many_lines,
-)]
+#[expect(deprecated, reason = "To allow deprecated login methods")]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn login_route(
     body: Ar<login::v3::Request>,
 ) -> Result<Ra<login::v3::Response>> {
@@ -252,8 +249,6 @@ pub(crate) async fn login_route(
 
     info!(%user_id, %device_id, "User logged in");
 
-    // Homeservers are still required to send the `home_server` field
-    #[allow(deprecated)]
     Ok(Ra(login::v3::Response {
         user_id,
         access_token: token,

src/api/client_server/sync.rs

@@ -67,7 +67,7 @@ use crate::{
 /// For left rooms:
 /// - If the user left after `since`: `prev_batch` token, empty state (TODO:
 ///   subset of the state at the point of the leave)
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn sync_events_route(
     body: Ar<sync_events::v3::Request>,
 ) -> Result<Ra<sync_events::v3::Response>, Ra<UiaaResponse>> {
@@ -449,7 +449,7 @@ pub(crate) async fn sync_events_route(
 }
 
 #[tracing::instrument(skip_all, fields(room_id = %room_id))]
-#[allow(clippy::too_many_arguments, clippy::too_many_lines)]
+#[expect(clippy::too_many_arguments)]
 async fn load_joined_room(
     sender_user: &UserId,
     sender_device: &DeviceId,
@@ -1121,7 +1121,7 @@ fn share_encrypted_room(
         .any(|encrypted| encrypted))
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn sync_events_v4_route(
     body: Ar<sync_events::v4::Request>,
 ) -> Result<Ra<sync_events::v4::Response>, Ra<UiaaResponse>> {

src/api/ruma_wrapper/axum.rs

@@ -50,7 +50,7 @@ struct ArPieces {
 
 /// Non-generic part of [`Ar::from_request()`]. Splitting this out reduces
 /// binary size by ~10%.
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 async fn ar_from_request_inner(
     req: axum::extract::Request,
     metadata: Metadata,

src/api/server_server.rs

@@ -372,7 +372,6 @@ fn add_port_to_hostname(destination_str: &str) -> FedDest {
 /// Implemented according to the specification at <https://matrix.org/docs/spec/server_server/r0.1.4#resolving-server-names>
 /// Numbers in comments below refer to bullet points in linked section of
 /// specification
-#[allow(clippy::too_many_lines)]
 #[tracing::instrument(ret(level = "debug"))]
 async fn find_actual_destination(
     destination: &'_ ServerName,
@@ -729,7 +728,7 @@ pub(crate) fn parse_incoming_pdu(
 /// # `PUT /_matrix/federation/v1/send/{txnId}`
 ///
 /// Push EDUs and PDUs to this server.
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn send_transaction_message_route(
     body: Ar<send_transaction_message::v1::Request>,
 ) -> Result<Ra<send_transaction_message::v1::Response>> {
@@ -1561,7 +1560,7 @@ pub(crate) async fn create_join_event_template_route(
     }))
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 async fn create_join_event(
     sender_servername: &ServerName,
     room_id: &RoomId,
@@ -1706,7 +1705,7 @@ async fn create_join_event(
 /// # `PUT /_matrix/federation/v1/send_join/{roomId}/{eventId}`
 ///
 /// Submits a signed join event.
-#[allow(deprecated)]
+#[expect(deprecated, reason = "support for deprecated API")]
 pub(crate) async fn create_join_event_v1_route(
     body: Ar<create_join_event::v1::Request>,
 ) -> Result<Ra<create_join_event::v1::Response>> {
@@ -1750,7 +1749,7 @@ pub(crate) async fn create_join_event_v2_route(
 /// # `PUT /_matrix/federation/v2/invite/{roomId}/{eventId}`
 ///
 /// Invites a remote user to a room.
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 pub(crate) async fn create_invite_route(
     body: Ar<create_invite::v2::Request>,
 ) -> Result<Ra<create_invite::v2::Response>> {

src/cli/serve.rs

@@ -124,7 +124,7 @@ async fn federation_self_test() -> Result<()> {
     Ok(())
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines)]
 async fn run_server() -> Result<(), error::Serve> {
     use error::Serve as Error;
 
@@ -337,7 +337,7 @@ fn legacy_media_routes(config: &Config) -> Router {
     }
 }
 
-#[allow(clippy::too_many_lines)]
+#[expect(clippy::too_many_lines, reason = "there's a lot of routes")]
 fn client_routes() -> Router {
     use client_server as c2s;
 
@@ -705,7 +705,6 @@ pub(crate) trait RumaHandler<T> {
 macro_rules! impl_ruma_handler {
     ( $($ty:ident),* $(,)? ) => {
         #[axum::async_trait]
-        #[allow(non_snake_case)]
         impl<Req, Resp, E, F, Fut, $($ty,)*>
             RumaHandler<($($ty,)* Ar<Req>,)> for F
         where
@@ -728,7 +727,10 @@ macro_rules! impl_ruma_handler {
                         path,
                         on(
                             method_filter,
-                            |$( $ty: $ty, )* req: Ar<Req>| async move {
+                            |$(#[expect(
+                                    non_snake_case,
+                                    reason = "reuse of macro fragments",
+                                )] $ty: $ty, )* req: Ar<Req>| async move {
                                 let span = info_span!(
                                     "run_ruma_handler",
                                     auth.user = ?req.sender_user,

src/config.rs

@@ -27,7 +27,7 @@ use proxy::ProxyConfig;
 pub(crate) static DEFAULT_PATH: Lazy<PathBuf> =
     Lazy::new(|| [env!("CARGO_PKG_NAME"), "config.toml"].iter().collect());
 
-#[allow(clippy::struct_excessive_bools)]
+#[expect(clippy::struct_excessive_bools, reason = "config schema struct")]
 #[derive(Debug, Deserialize)]
 pub(crate) struct Config {
     #[serde(default = "false_fn")]

src/database.rs

@@ -95,13 +95,17 @@ pub(crate) struct KeyValueDatabase {
     pub(super) roomuserid_lastprivatereadupdate: Arc<dyn KvTree>,
 
     // PresenceId = RoomId + Count + UserId
-    // This exists in the database already but is currently unused
-    #[allow(dead_code)]
+    #[expect(
+        dead_code,
+        reason = "This exists in the database already but is currently unused"
+    )]
     pub(super) presenceid_presence: Arc<dyn KvTree>,
 
     // LastPresenceUpdate = Count
-    // This exists in the database already but is currently unused
-    #[allow(dead_code)]
+    #[expect(
+        dead_code,
+        reason = "This exists in the database already but is currently unused"
+    )]
     pub(super) userid_lastpresenceupdate: Arc<dyn KvTree>,
 
     // Trees "owned" by `self::key_value::rooms`
@@ -317,7 +321,7 @@ impl KeyValueDatabase {
         not(any(feature = "rocksdb", feature = "sqlite")),
         allow(unreachable_code)
     )]
-    #[allow(clippy::too_many_lines)]
+    #[expect(clippy::too_many_lines)]
     pub(crate) fn load_or_create(config: &Config) -> Result<KeyValueDatabase> {
         Self::check_db_setup(config)?;
 
@@ -478,7 +482,7 @@ impl KeyValueDatabase {
                     .try_into()
                     .expect("pdu cache capacity fits into usize"),
             )),
-            #[allow(
+            #[expect(
                 clippy::as_conversions,
                 clippy::cast_sign_loss,
                 clippy::cast_possible_truncation
@@ -486,7 +490,7 @@ impl KeyValueDatabase {
             auth_chain_cache: Mutex::new(LruCache::new(
                 (100_000.0 * config.cache_capacity_modifier) as usize,
             )),
-            #[allow(
+            #[expect(
                 clippy::as_conversions,
                 clippy::cast_sign_loss,
                 clippy::cast_possible_truncation
@@ -494,7 +498,7 @@ impl KeyValueDatabase {
             shorteventid_cache: Mutex::new(LruCache::new(
                 (100_000.0 * config.cache_capacity_modifier) as usize,
             )),
-            #[allow(
+            #[expect(
                 clippy::as_conversions,
                 clippy::cast_sign_loss,
                 clippy::cast_possible_truncation
@@ -502,7 +506,7 @@ impl KeyValueDatabase {
             eventidshort_cache: Mutex::new(LruCache::new(
                 (100_000.0 * config.cache_capacity_modifier) as usize,
             )),
-            #[allow(
+            #[expect(
                 clippy::as_conversions,
                 clippy::cast_sign_loss,
                 clippy::cast_possible_truncation
@@ -510,7 +514,7 @@ impl KeyValueDatabase {
             shortstatekey_cache: Mutex::new(LruCache::new(
                 (100_000.0 * config.cache_capacity_modifier) as usize,
             )),
-            #[allow(
+            #[expect(
                 clippy::as_conversions,
                 clippy::cast_sign_loss,
                 clippy::cast_possible_truncation
@@ -531,7 +535,7 @@ impl KeyValueDatabase {
     ///
     /// If it is not possible to migrate the database to the current version,
     /// returns an error.
-    #[allow(clippy::too_many_lines)]
+    #[expect(clippy::too_many_lines)]
     pub(crate) async fn apply_migrations(&self) -> Result<()> {
         // If the database has any data, perform data migrations before starting
         let latest_database_version = 13;

src/database/abstraction/rocksdb.rs

@@ -72,10 +72,11 @@ fn db_options(max_open_files: i32, rocksdb_cache: &Cache) -> Options {
 
 impl KeyValueDatabaseEngine for Arc<Engine> {
     fn open(config: &Config) -> Result<Self> {
-        #[allow(
+        #[expect(
             clippy::as_conversions,
             clippy::cast_sign_loss,
-            clippy::cast_possible_truncation
+            clippy::cast_possible_truncation,
+            reason = "saturating to usize is fine"
         )]
         let cache_capacity_bytes =
             (config.database.cache_capacity_mb * 1024.0 * 1024.0) as usize;
@@ -144,7 +145,11 @@ impl KeyValueDatabaseEngine for Arc<Engine> {
         }))
     }
 
-    #[allow(clippy::as_conversions, clippy::cast_precision_loss)]
+    #[expect(
+        clippy::as_conversions,
+        clippy::cast_precision_loss,
+        reason = "these are just informational"
+    )]
     fn memory_usage(&self) -> Result<String> {
         let stats =
             get_memory_usage_stats(Some(&[&self.rocks]), Some(&[&self.cache]))?;

src/database/abstraction/sqlite.rs

@@ -124,11 +124,12 @@ impl KeyValueDatabaseEngine for Arc<Engine> {
         // 2. divide by permanent connections + permanent iter connections +
         //    write connection
         // 3. round down to nearest integer
-        #[allow(
+        #[expect(
             clippy::as_conversions,
             clippy::cast_possible_truncation,
             clippy::cast_precision_loss,
-            clippy::cast_sign_loss
+            clippy::cast_sign_loss,
+            reason = "saturating to u32 is fine"
         )]
         let cache_size_per_thread =
             ((config.database.cache_capacity_mb * 1024.0)

src/database/abstraction/watchers.rs

@@ -9,7 +9,10 @@ use tokio::sync::watch;
 
 #[derive(Default)]
 pub(super) struct Watchers {
-    #[allow(clippy::type_complexity)]
+    #[expect(
+        clippy::type_complexity,
+        reason = "not actually all that complex"
+    )]
     watchers:
         RwLock<HashMap<Vec<u8>, (watch::Sender<()>, watch::Receiver<()>)>>,
 }

src/database/key_value/rooms/edus/read_receipt.rs

@@ -53,7 +53,7 @@ impl service::rooms::edus::read_receipt::Data for KeyValueDatabase {
     }
 
     #[tracing::instrument(skip(self))]
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn readreceipts_since<'a>(
         &'a self,
         room_id: &RoomId,

src/database/key_value/rooms/search.rs

@@ -64,7 +64,7 @@ impl service::rooms::search::Data for KeyValueDatabase {
     }
 
     #[tracing::instrument(skip(self))]
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn search_pdus<'a>(
         &'a self,
         room_id: &RoomId,

src/database/key_value/rooms/state_cache.rs

@@ -482,7 +482,7 @@ impl service::rooms::state_cache::Data for KeyValueDatabase {
     }
 
     /// Returns an iterator over all rooms a user was invited to.
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     #[tracing::instrument(skip(self))]
     fn rooms_invited<'a>(
         &'a self,
@@ -575,7 +575,7 @@ impl service::rooms::state_cache::Data for KeyValueDatabase {
     }
 
     /// Returns an iterator over all rooms a user left.
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     #[tracing::instrument(skip(self))]
     fn rooms_left<'a>(
         &'a self,

src/error.rs

@@ -35,9 +35,6 @@ impl fmt::Display for DisplayWithSources<'_> {
 }
 
 /// Top-level errors
-// Missing docs are allowed here since that kind of information should be
-// encoded in the error messages themselves anyway.
-#[allow(missing_docs)]
 #[derive(Error, Debug)]
 pub(crate) enum Main {
     #[error(transparent)]
@@ -45,9 +42,6 @@ pub(crate) enum Main {
 }
 
 /// Errors returned from the `serve` CLI subcommand.
-// Missing docs are allowed here since that kind of information should be
-// encoded in the error messages themselves anyway.
-#[allow(missing_docs)]
 #[derive(Error, Debug)]
 pub(crate) enum ServeCommand {
     #[error("failed to load configuration")]
@@ -70,9 +64,6 @@ pub(crate) enum ServeCommand {
 }
 
 /// Error generated if `server_name` has changed or if checking this failed
-// Missing docs are allowed here since that kind of information should be
-// encoded in the error messages themselves anyway.
-#[allow(missing_docs)]
 #[derive(Error, Debug)]
 pub(crate) enum ServerNameChanged {
     #[error("failed to check if there are any users")]
@@ -86,9 +77,6 @@ pub(crate) enum ServerNameChanged {
 }
 
 /// Observability initialization errors
-// Missing docs are allowed here since that kind of information should be
-// encoded in the error messages themselves anyway.
-#[allow(missing_docs)]
 #[derive(Error, Debug)]
 pub(crate) enum Observability {
     // Upstream's documentation on what this error means is very sparse
@@ -104,9 +92,6 @@ pub(crate) enum Observability {
 }
 
 /// Configuration errors
-// Missing docs are allowed here since that kind of information should be
-// encoded in the error messages themselves anyway.
-#[allow(missing_docs)]
 #[derive(Error, Debug)]
 pub(crate) enum Config {
     #[error("failed to find configuration file")]
@@ -123,9 +108,6 @@ pub(crate) enum Config {
 }
 
 /// Errors that can occur while searching for a config file
-// Missing docs are allowed here since that kind of information should be
-// encoded in the error messages themselves anyway.
-#[allow(missing_docs)]
 #[derive(Error, Debug)]
 pub(crate) enum ConfigSearch {
     #[error("XDG Base Directory error")]
@@ -136,9 +118,6 @@ pub(crate) enum ConfigSearch {
 }
 
 /// Errors serving traffic
-// Missing docs are allowed here since that kind of information should be
-// encoded in the error messages themselves anyway.
-#[allow(missing_docs)]
 #[derive(Error, Debug)]
 pub(crate) enum Serve {
     #[error("no listeners were specified in the configuration file")]

src/observability.rs

@@ -39,7 +39,7 @@ pub(crate) static METRICS: Lazy<Metrics> = Lazy::new(Metrics::new);
 /// Cleans up resources relating to observability when [`Drop`]ped
 pub(crate) struct Guard {
     /// Drop guard used to flush [`tracing_flame`] data on exit
-    #[allow(dead_code)]
+    #[expect(dead_code, reason = "only exists to be dropped")]
     flame_guard: Option<FlushGuard<BufWriter<File>>>,
 }
 
@@ -80,7 +80,10 @@ pub(crate) type FilterReloadHandle = Box<dyn ReloadHandle<EnvFilter> + Sync>;
 /// Collection of [`FilterReloadHandle`]s, allowing the filters for tracing
 /// backends to be changed dynamically. Handles may be [`None`] if the backend
 /// is disabled in the config.
-#[allow(clippy::missing_docs_in_private_items)]
+#[expect(
+    clippy::missing_docs_in_private_items,
+    reason = "mirrors config struct layout"
+)]
 pub(crate) struct FilterReloadHandles {
     pub(crate) traces: Option<FilterReloadHandle>,
     pub(crate) flame: Option<FilterReloadHandle>,
@@ -91,7 +94,7 @@ pub(crate) struct FilterReloadHandles {
 ///
 /// See also [`Metrics::record_lookup`].
 // Keep variants sorted
-#[allow(clippy::missing_docs_in_private_items)]
+#[expect(clippy::missing_docs_in_private_items)]
 #[derive(Clone, Copy, AsRefStr, IntoStaticStr)]
 pub(crate) enum Lookup {
     AppserviceInRoom,
@@ -208,7 +211,7 @@ pub(crate) fn init(
     let (log_layer, log_filter, _) =
         make_backend(true, &config.observability.logs.filter, || {
             /// Time format selection for `tracing_subscriber` at runtime
-            #[allow(clippy::missing_docs_in_private_items)]
+            #[expect(clippy::missing_docs_in_private_items, reason = "trivial")]
             enum TimeFormat {
                 SystemTime,
                 NoTime,

src/service.rs

@@ -99,7 +99,7 @@ impl Services {
                 },
                 state_accessor: rooms::state_accessor::Service {
                     db,
-                    #[allow(
+                    #[expect(
                         clippy::as_conversions,
                         clippy::cast_sign_loss,
                         clippy::cast_possible_truncation
@@ -107,7 +107,7 @@ impl Services {
                     server_visibility_cache: StdMutex::new(LruCache::new(
                         (100.0 * config.cache_capacity_modifier) as usize,
                     )),
-                    #[allow(
+                    #[expect(
                         clippy::as_conversions,
                         clippy::cast_sign_loss,
                         clippy::cast_possible_truncation
@@ -121,7 +121,7 @@ impl Services {
                 },
                 state_compressor: rooms::state_compressor::Service {
                     db,
-                    #[allow(
+                    #[expect(
                         clippy::as_conversions,
                         clippy::cast_sign_loss,
                         clippy::cast_possible_truncation

src/service/admin.rs

@@ -55,8 +55,10 @@ enum AdminCommand {
     /// # ```
     /// # yaml content here
     /// # ```
-    // Allowed because the doc comment gets parsed by our code later
-    #[allow(clippy::doc_markdown)]
+    #[expect(
+        clippy::doc_markdown,
+        reason = "the doc comment gets parsed by our code later"
+    )]
     RegisterAppservice,
 
     /// Unregister an appservice using its ID
@@ -104,8 +106,10 @@ enum AdminCommand {
     /// # ```
     /// # User list here
     /// # ```
-    // Allowed because the doc comment gets parsed by our code later
-    #[allow(clippy::doc_markdown)]
+    #[expect(
+        clippy::doc_markdown,
+        reason = "the doc comment gets parsed by our code later"
+    )]
     DeactivateAll {
         #[arg(short, long)]
         /// Remove users from their joined rooms
@@ -131,8 +135,10 @@ enum AdminCommand {
     /// # ```
     /// # PDU json content here
     /// # ```
-    // Allowed because the doc comment gets parsed by our code later
-    #[allow(clippy::doc_markdown)]
+    #[expect(
+        clippy::doc_markdown,
+        reason = "the doc comment gets parsed by our code later"
+    )]
     ParsePdu,
 
     /// Retrieve and print a PDU by ID from the Grapevine database
@@ -206,8 +212,10 @@ enum AdminCommand {
     /// # ```
     /// # json here
     /// # ```
-    // Allowed because the doc comment gets parsed by our code later
-    #[allow(clippy::doc_markdown)]
+    #[expect(
+        clippy::doc_markdown,
+        reason = "the doc comment gets parsed by our code later"
+    )]
     SignJson,
 
     /// Verify json signatures
@@ -215,8 +223,10 @@ enum AdminCommand {
     /// # ```
     /// # json here
     /// # ```
-    // Allowed because the doc comment gets parsed by our code later
-    #[allow(clippy::doc_markdown)]
+    #[expect(
+        clippy::doc_markdown,
+        reason = "the doc comment gets parsed by our code later"
+    )]
     VerifyJson,
 
     /// Dynamically change a tracing backend's filter string
@@ -411,7 +421,6 @@ impl Service {
         AdminCommand::try_parse_from(argv).map_err(|error| error.to_string())
     }
 
-    #[allow(clippy::too_many_lines)]
     #[tracing::instrument(skip(self, body))]
     async fn process_admin_command(
         &self,
@@ -1286,7 +1295,6 @@ impl Service {
     /// Users in this room are considered admins by grapevine, and the room can
     /// be used to issue admin commands by talking to the server user inside
     /// it.
-    #[allow(clippy::too_many_lines)]
     #[tracing::instrument(skip(self))]
     pub(crate) async fn create_admin_room(&self) -> Result<()> {
         let room_id = RoomId::new(services().globals.server_name());
@@ -1527,8 +1535,7 @@ impl Service {
     ///
     /// Errors are propagated from the database, and will have None if there is
     /// no admin room
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
+    #[expect(clippy::unused_self, reason = "uses services()")]
     pub(crate) fn get_admin_room(&self) -> Result<Option<OwnedRoomId>> {
         services()
             .rooms

src/service/globals.rs

@@ -110,7 +110,7 @@ pub(crate) struct RotationHandler(
     // TODO: Determine if it's safe to delete this field. I'm not deleting it
     // right now because I'm unsure what implications that would have for how
     // the sender expects to work.
-    #[allow(dead_code)] broadcast::Receiver<()>,
+    #[expect(dead_code, reason = "see comment")] broadcast::Receiver<()>,
 );
 
 impl RotationHandler {
@@ -310,8 +310,6 @@ impl Service {
     /// Matrix resource ownership is based on the server name; changing it
     /// requires recreating the database from scratch. This check needs to be
     /// done before background tasks are started to avoid data races.
-    // Allowed because this function calls `services()`
-    #[allow(clippy::unused_self)]
     pub(crate) fn err_if_server_name_changed(
         &self,
     ) -> Result<(), crate::error::ServerNameChanged> {
@@ -544,7 +542,6 @@ impl Service {
     /// Filters the key map of multiple servers down to keys that should be
     /// accepted given the expiry time, room version, and timestamp of the
     /// paramters
-    #[allow(clippy::unused_self)]
     pub(crate) fn filter_keys_server_map(
         &self,
         keys: BTreeMap<String, SigningKeys>,
@@ -561,7 +558,7 @@ impl Service {
 
     /// Filters the keys of a single server down to keys that should be accepted
     /// given the expiry time, room version, and timestamp of the paramters
-    #[allow(clippy::unused_self)]
+    #[expect(clippy::unused_self)]
     pub(crate) fn filter_keys_single_server(
         &self,
         keys: SigningKeys,

src/service/media.rs

@@ -19,7 +19,6 @@ pub(crate) struct FileMeta {
     //
     // TODO: Write a database migration to get rid of this and instead store
     // only the filename instead of the entire `Content-Disposition` header.
-    #[allow(dead_code)]
     pub(crate) content_disposition: Option<String>,
     pub(crate) content_type: Option<String>,
 }

src/service/rooms/auth_chain.rs

@@ -49,9 +49,13 @@ impl Service {
         for id in starting_events {
             let short =
                 services().rooms.short.get_or_create_shorteventid(&id)?;
-            // I'm afraid to change this in case there is accidental reliance on
-            // the truncation
-            #[allow(clippy::as_conversions, clippy::cast_possible_truncation)]
+            #[expect(
+                clippy::as_conversions,
+                clippy::cast_possible_truncation,
+                reason = "I'm afraid to change this in case there is \
+                          accidental
+                reliance on the truncation"
+            )]
             let bucket_id = (short.get() % NUM_BUCKETS as u64) as usize;
             buckets[bucket_id].insert((short, id.clone()));
             i += 1;

src/service/rooms/edus/read_receipt/data.rs

@@ -15,7 +15,7 @@ pub(crate) trait Data: Send + Sync {
 
     /// Returns an iterator over the most recent read receipts in a room that
     /// happened after the event with id `since`.
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn readreceipts_since<'a>(
         &'a self,
         room_id: &RoomId,
@@ -40,7 +40,7 @@ pub(crate) trait Data: Send + Sync {
 
     /// Returns the private read marker.
     // TODO: Implement MSC2285
-    #[allow(dead_code)]
+    #[expect(dead_code, reason = "private read receipts are unimplemented")]
     fn private_read_get(
         &self,
         room_id: &RoomId,
@@ -49,7 +49,7 @@ pub(crate) trait Data: Send + Sync {
 
     /// Returns the count of the last typing update in this room.
     // TODO: Implement MSC2285
-    #[allow(dead_code)]
+    #[expect(dead_code, reason = "private read receipts are unimplemented")]
     fn last_privateread_update(
         &self,
         user_id: &UserId,

src/service/rooms/event_handler.rs

@@ -312,7 +312,7 @@ impl Service {
         r
     }
 
-    #[allow(clippy::too_many_arguments)]
+    #[expect(clippy::too_many_arguments)]
     #[tracing::instrument(skip(self, origin, room_id, value, pub_key_map))]
     fn handle_outlier_pdu<'a>(
         &'a self,
@@ -1433,7 +1433,7 @@ impl Service {
     }
 
     #[tracing::instrument(skip_all)]
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     async fn fetch_unknown_prev_events(
         &self,
         origin: &ServerName,
@@ -1709,7 +1709,7 @@ impl Service {
         Ok(())
     }
 
-    #[allow(clippy::too_many_lines)]
+    #[expect(clippy::too_many_lines)]
     pub(crate) async fn fetch_join_signing_keys(
         &self,
         event: &create_join_event::v2::Response,
@@ -1840,8 +1840,6 @@ impl Service {
     }
 
     /// Returns Ok if the acl allows the server
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
     #[tracing::instrument(skip_all)]
     pub(crate) fn acl_check(
         &self,

src/service/rooms/lazy_loading.rs

@@ -11,7 +11,7 @@ use crate::Result;
 pub(crate) struct Service {
     pub(crate) db: &'static dyn Data,
 
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     pub(crate) lazy_load_waiting: Mutex<
         HashMap<
             (OwnedUserId, OwnedDeviceId, OwnedRoomId, PduCount),

src/service/rooms/pdu_metadata.rs

@@ -45,7 +45,7 @@ impl Service {
         }
     }
 
-    #[allow(clippy::too_many_arguments, clippy::too_many_lines)]
+    #[expect(clippy::too_many_arguments)]
     #[tracing::instrument(skip(self))]
     pub(crate) fn paginate_relations_with_filter(
         &self,

src/service/rooms/pdu_metadata/data.rs

@@ -9,7 +9,7 @@ use crate::{
 
 pub(crate) trait Data: Send + Sync {
     fn add_relation(&self, from: u64, to: u64) -> Result<()>;
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn relations_until<'a>(
         &'a self,
         user_id: &'a UserId,

src/service/rooms/search/data.rs

@@ -20,7 +20,7 @@ pub(crate) trait Data: Send + Sync {
         message_body: &str,
     ) -> Result<()>;
 
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn search_pdus<'a>(
         &'a self,
         room_id: &RoomId,

src/service/rooms/spaces.rs

@@ -50,7 +50,6 @@ pub(crate) struct Service {
 }
 
 impl Service {
-    #[allow(clippy::too_many_lines)]
     #[tracing::instrument(skip(self))]
     pub(crate) async fn get_hierarchy(
         &self,
@@ -326,7 +325,6 @@ impl Service {
         })
     }
 
-    #[allow(clippy::too_many_lines)]
     #[tracing::instrument(skip(self, children))]
     fn get_room_chunk(
         &self,
@@ -532,8 +530,7 @@ impl Service {
         }
     }
 
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
+    #[expect(clippy::unused_self, reason = "uses services()")]
     fn handle_simplified_join_rule(
         &self,
         join_rule: &SpaceRoomJoinRule,

src/service/rooms/state_accessor.rs

@@ -396,8 +396,6 @@ impl Service {
         )
     }
 
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
     #[tracing::instrument(skip(self), ret(level = "trace"))]
     pub(crate) fn user_can_invite(
         &self,

src/service/rooms/state_cache.rs

@@ -175,8 +175,7 @@ impl Service {
     }
 
     /// Copy `m.tag` account data to an upgraded room.
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
+    #[expect(clippy::unused_self, reason = "uses services()")]
     fn copy_upgraded_account_data_tag(
         &self,
         user_id: &UserId,
@@ -206,8 +205,7 @@ impl Service {
     }
 
     /// Copy references in `m.direct` account data events to an upgraded room.
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
+    #[expect(clippy::unused_self, reason = "uses services()")]
     fn copy_upgraded_account_data_direct(
         &self,
         user_id: &UserId,

src/service/rooms/state_cache/data.rs

@@ -93,7 +93,7 @@ pub(crate) trait Data: Send + Sync {
     ) -> Box<dyn Iterator<Item = Result<OwnedRoomId>> + 'a>;
 
     /// Returns an iterator over all rooms a user was invited to.
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn rooms_invited<'a>(
         &'a self,
         user_id: &UserId,
@@ -116,7 +116,7 @@ pub(crate) trait Data: Send + Sync {
     ) -> Result<Option<Vec<Raw<AnyStrippedStateEvent>>>>;
 
     /// Returns an iterator over all rooms a user left.
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn rooms_left<'a>(
         &'a self,
         user_id: &UserId,
@@ -132,6 +132,6 @@ pub(crate) trait Data: Send + Sync {
     fn is_invited(&self, user_id: &UserId, room_id: &RoomId) -> Result<bool>;
 
     // TODO: Use this when implementing sync filtering
-    #[allow(dead_code)]
+    #[expect(dead_code, reason = "sync filtering is unimplemented")]
     fn is_left(&self, user_id: &UserId, room_id: &RoomId) -> Result<bool>;
 }

src/service/rooms/state_compressor.rs

@@ -31,7 +31,6 @@ pub(crate) struct CompressedStateLayer {
 pub(crate) struct Service {
     pub(crate) db: &'static dyn Data,
 
-    #[allow(clippy::type_complexity)]
     pub(crate) stateinfo_cache:
         Mutex<LruCache<ShortStateHash, Vec<CompressedStateLayer>>>,
 }
@@ -75,7 +74,6 @@ impl CompressedStateEvent {
 impl Service {
     /// Returns a stack with info on shortstatehash, full state, added diff and
     /// removed diff for the selected shortstatehash and each parent layer.
-    #[allow(clippy::type_complexity)]
     #[tracing::instrument(skip(self))]
     pub(crate) fn load_shortstatehash_info(
         &self,
@@ -130,8 +128,7 @@ impl Service {
         Ok(response)
     }
 
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
+    #[expect(clippy::unused_self, reason = "uses services()")]
     pub(crate) fn compress_state_event(
         &self,
         shortstatekey: ShortStateKey,
@@ -147,8 +144,7 @@ impl Service {
     }
 
     /// Returns shortstatekey, event id
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
+    #[expect(clippy::unused_self, reason = "uses services()")]
     pub(crate) fn parse_compressed_state_event(
         &self,
         compressed_event: &CompressedStateEvent,
@@ -180,7 +176,6 @@ impl Service {
     ///   for this layer
     /// * `parent_states` - A stack with info on shortstatehash, full state,
     ///   added diff and removed diff for each parent layer
-    #[allow(clippy::type_complexity)]
     #[tracing::instrument(skip(
         self,
         statediffnew,
@@ -303,7 +298,7 @@ impl Service {
 
     /// Returns the new shortstatehash, and the state diff from the previous
     /// room state
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     #[tracing::instrument(skip(self, new_state_ids_compressed))]
     pub(crate) fn save_state(
         &self,

src/service/rooms/threads/data.rs

@@ -6,7 +6,7 @@ use ruma::{
 use crate::{service::rooms::timeline::PduId, PduEvent, Result};
 
 pub(crate) trait Data: Send + Sync {
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn threads_until<'a>(
         &'a self,
         user_id: &'a UserId,

src/service/rooms/timeline.rs

@@ -683,7 +683,7 @@ impl Service {
         Ok(pdu_id)
     }
 
-    #[allow(clippy::too_many_lines)]
+    #[expect(clippy::too_many_lines)]
     pub(crate) fn create_hash_and_sign_event(
         &self,
         pdu_builder: PduBuilder,

src/service/rooms/timeline/data.rs

@@ -82,7 +82,7 @@ pub(crate) trait Data: Send + Sync {
     /// Returns an iterator over all events and their tokens in a room that
     /// happened before the event with id `until` in reverse-chronological
     /// order.
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn pdus_until<'a>(
         &'a self,
         user_id: &UserId,
@@ -92,7 +92,7 @@ pub(crate) trait Data: Send + Sync {
 
     /// Returns an iterator over all events in a room that happened after the
     /// event with id `from` in chronological order.
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     fn pdus_after<'a>(
         &'a self,
         user_id: &UserId,

src/service/sending/data.rs

@@ -4,7 +4,6 @@ use super::{Destination, RequestKey, SendingEventType};
 use crate::Result;
 
 pub(crate) trait Data: Send + Sync {
-    #[allow(clippy::type_complexity)]
     fn active_requests<'a>(
         &'a self,
     ) -> Box<

src/service/users.rs

@@ -34,7 +34,7 @@ pub(crate) struct SlidingSyncCache {
 
 pub(crate) struct Service {
     pub(crate) db: &'static dyn Data,
-    #[allow(clippy::type_complexity)]
+    #[expect(clippy::type_complexity)]
     pub(crate) connections: Mutex<
         BTreeMap<
             (OwnedUserId, OwnedDeviceId, String),
@@ -58,7 +58,7 @@ impl Service {
         self.connections.lock().unwrap().remove(&(user_id, device_id, conn_id));
     }
 
-    #[allow(clippy::too_many_lines)]
+    #[expect(clippy::too_many_lines)]
     pub(crate) fn update_sync_request_with_cache(
         &self,
         user_id: OwnedUserId,
@@ -255,8 +255,10 @@ impl Service {
     }
 
     /// Check if a user is an admin
-    // Allowed because this function uses `services()`
-    #[allow(clippy::unused_self)]
+    #[expect(
+        clippy::unused_self,
+        reason = "Allowed because this function uses `services()`"
+    )]
     pub(crate) fn is_admin(&self, user_id: &UserId) -> Result<bool> {
         services().admin.get_admin_room()?.map_or(Ok(false), |admin_room_id| {
             services().rooms.state_cache.is_joined(user_id, &admin_room_id)

src/utils.rs

@@ -21,8 +21,11 @@ use ruma::{
 
 use crate::{Error, Result};
 
-// Hopefully we have a better chat protocol in 530 years
-#[allow(clippy::as_conversions, clippy::cast_possible_truncation)]
+#[expect(
+    clippy::as_conversions,
+    clippy::cast_possible_truncation,
+    reason = "Hopefully we have a better chat protocol in 530 years"
+)]
 pub(crate) fn millis_since_unix_epoch() -> u64 {
     SystemTime::now()
         .duration_since(UNIX_EPOCH)
@@ -252,7 +255,10 @@ pub(crate) fn dbg_truncate_str(s: &str, mut max_len: usize) -> Cow<'_, str> {
     if s.len() <= max_len {
         s.into()
     } else {
-        #[allow(clippy::string_slice)] // we checked it's at a char boundary
+        #[expect(
+            clippy::string_slice,
+            reason = "we checked it's at a char boundary"
+        )]
         format!("{}...", &s[..max_len]).into()
     }
 }

src/utils/error.rs

@@ -16,7 +16,10 @@ use crate::Ra;
 pub(crate) type Result<T, E = Error> = std::result::Result<T, E>;
 
 #[derive(Error, Debug)]
-#[allow(clippy::error_impl_error)]
+#[expect(
+    clippy::error_impl_error,
+    reason = "This is our one and only Error struct"
+)]
 pub(crate) enum Error {
     #[cfg(feature = "sqlite")]
     #[error(

src/utils/room_version.rs

@@ -35,9 +35,11 @@ pub(crate) struct RoomVersion {
     pub(crate) redaction_event_redacts_in_content: bool,
 }
 
-// Allowed so that we can use struct-update syntax for incremental changes
-// between versions even when all fields change.
-#[allow(clippy::needless_update)]
+#[expect(
+    clippy::needless_update,
+    reason = "so that we can use struct-update syntax for incremental changes \
+              between versions even when all fields change"
+)]
 mod known_versions {
     use super::RoomVersion;