Explain a panic in test case net::tcp::tests::double_bind

diff --git a/src/libstd/net/tcp.rs b/src/libstd/net/tcp.rs
index 86ecb10edf2f9e55c9585776ff3090acc8a56163..c2bc85ae57617b6b57f68a889610afad4f5cf0e6 100644 (file)
--- a/src/libstd/net/tcp.rs
+++ b/src/libstd/net/tcp.rs
@@ -1187,9 +1187,13 @@ fn partial_read() {
     #[test]
     fn double_bind() {
         each_ip(&mut |addr| {
-            let _listener = t!(TcpListener::bind(&addr));
+            let listener1 = t!(TcpListener::bind(&addr));
             match TcpListener::bind(&addr) {
-                Ok(..) => panic!(),
+                Ok(listener2) => panic!(
+                    "This system (perhaps due to options set by TcpListener::bind) \
+                     permits double binding: {:?} and {:?}",
+                    listener1, listener2
+                ),
                 Err(e) => {
                     assert!(e.kind() == ErrorKind::ConnectionRefused ||
                             e.kind() == ErrorKind::Other ||