request: Allow nullable disconnect explaination

Author: ids1024

src/calloop.rs

@@ -140,7 +140,7 @@ fn handle_result(
         } else {
             eis::connection::DisconnectReason::Protocol
         };
-        connection.disconnected(reason, &err.to_string());
+        connection.disconnected(reason, Some(&err.to_string()));
         let _ = connection.flush();
     }
 
@@ -168,7 +168,7 @@ fn process_handshake(
             if !handle.has_interface("ei_seat") || !handle.has_interface("ei_device") {
                 handle.disconnected(
                     eis::connection::DisconnectReason::Protocol,
-                    "Need `ei_seat` and `ei_device`",
+                    Some("Need `ei_seat` and `ei_device`"),
                 );
                 let _ = request_converter.handle().flush();
                 return Err(HandshakeError::MissingInterface.into());

src/request.rs

@@ -75,8 +75,7 @@ impl Connection {
     ///
     /// Will panic if an internal Mutex is poisoned.
     // TODO(axka, 2025-07-08): rename to something imperative like `notify_disconnection`
-    // TODO(axka, 2025-07-08): `explanation` must support NULL: https://gitlab.freedesktop.org/libinput/libei/-/commit/267716a7609730914b24adf5860ec8d2cf2e7636
-    pub fn disconnected(&self, reason: DisconnectReason, explanation: &str) {
+    pub fn disconnected(&self, reason: DisconnectReason, explanation: Option<&str>) {
         let seats = self
             .0
             .seats
@@ -89,7 +88,7 @@ impl Connection {
             seat.remove();
         }
         self.connection()
-            .disconnected(self.last_serial(), reason, Some(explanation));
+            .disconnected(self.last_serial(), reason, explanation);
     }
 
     /// Sends buffered messages. Call after you're finished with sending events.