Rollup merge of #139836 - glyn:test-mpmc-receiver-cloning, r=jhpratt

Basic tests of MPMC receiver cloning

Ref: https://github.com/rust-lang/rust/issues/126840#issuecomment-2802321146

library/std/tests/sync/mpmc.rs

@@ -63,6 +63,24 @@ fn smoke_port_gone() {
     assert!(tx.send(1).is_err());
 }
 
+#[test]
+fn smoke_receiver_clone() {
+    let (tx, rx) = channel::<i32>();
+    let rx2 = rx.clone();
+    drop(rx);
+    tx.send(1).unwrap();
+    assert_eq!(rx2.recv().unwrap(), 1);
+}
+
+#[test]
+fn smoke_receiver_clone_port_gone() {
+    let (tx, rx) = channel::<i32>();
+    let rx2 = rx.clone();
+    drop(rx);
+    drop(rx2);
+    assert!(tx.send(1).is_err());
+}
+
 #[test]
 fn smoke_shared_port_gone() {
     let (tx, rx) = channel::<i32>();
@@ -124,6 +142,18 @@ fn chan_gone_concurrent() {
     while rx.recv().is_ok() {}
 }
 
+#[test]
+fn receiver_cloning() {
+    let (tx, rx) = channel::<i32>();
+    let rx2 = rx.clone();
+
+    tx.send(1).unwrap();
+    tx.send(2).unwrap();
+
+    assert_eq!(rx2.recv(), Ok(1));
+    assert_eq!(rx.recv(), Ok(2));
+}
+
 #[test]
 fn stress() {
     let count = if cfg!(miri) { 100 } else { 10000 };