Auto merge of #34731 - GGist:fix_sync_try_recv, r=alexcrichton

Check for data in Receiver::try_recv before reporting disconnect

Fixes #34711

r? @alexcrichton

src/libstd/sync/mpsc/mod.rs

@@ -2180,6 +2180,15 @@ mod sync_tests {
         assert!(rx.recv().is_err());
     }
 
+    #[test]
+    fn oneshot_single_thread_try_recv_closed_with_data() {
+        let (tx, rx) = sync_channel::<i32>(1);
+        tx.send(10).unwrap();
+        drop(tx);
+        assert_eq!(rx.try_recv(), Ok(10));
+        assert_eq!(rx.try_recv(), Err(TryRecvError::Disconnected));
+    }
+
     #[test]
     fn oneshot_single_thread_peek_data() {
         let (tx, rx) = sync_channel::<i32>(1);

src/libstd/sync/mpsc/sync.rs

@@ -309,7 +309,7 @@ impl<T> Packet<T> {
         let mut guard = self.lock.lock().unwrap();
 
         // Easy cases first
-        if guard.disconnected { return Err(Disconnected) }
+        if guard.disconnected && guard.buf.size() == 0 { return Err(Disconnected) }
         if guard.buf.size() == 0 { return Err(Empty) }
 
         // Be sure to wake up neighbors