Spurious unwrap_err() of Ok at 'net::tcp::tests::connect_timeout_unbound' on Windows

[kennytm]

Symptom: On Windows, the libstd test net::tcp::tests::connect_timeout_unbound panicked for unexpectedly connected to a local closed TCP socket without timing out.

---- net::tcp::tests::connect_timeout_unbound stdout ----
thread 'net::tcp::tests::connect_timeout_unbound' panicked at 'called `Result::unwrap_err()` on an `Ok` value: TcpStream { addr: V4(127.0.0.1:3434), peer: V4(127.0.0.1:3434), socket: 1028 }', libcore\result.rs:945:5

Previous instances:

• 2018-05-19T07:41:59Z — Turn deprecation lint legacy_imports into a hard error #50760 (comment) (i686-msvc-1)
• 2018-06-04T15:32:27Z — Select Polonius algorithm via POLONIUS_ALGORITHM environment variable #51246 (comment) (i686-mingw-1)
• 2018-06-30T14:00:20Z — optimize places_conflict to avoid complex vectors etc #51849 (comment) (x86_64-mingw)
• 2018-07-21T18:51:09Z — Remove highlighting from secondary messages #51485 (comment) (i686-msvc-1)

[kennytm]

From the logs, the TCP port of both the TcpStream (self) and TcpListener (socket, dropped) are the same.

• Turn deprecation lint legacy_imports into a hard error #50760: TcpStream { addr: V4(127.0.0.1:3329), peer: V4(127.0.0.1:3329), socket: 408 }
• Select Polonius algorithm via POLONIUS_ALGORITHM environment variable #51246: TcpStream { addr: V4(127.0.0.1:3648), peer: V4(127.0.0.1:3648), socket: 720 }
• optimize places_conflict to avoid complex vectors etc #51849: TcpStream { addr: V4(127.0.0.1:3605), peer: V4(127.0.0.1:3605), socket: 728 }
• Remove highlighting from secondary messages #51485: TcpStream { addr: V4(127.0.0.1:3434), peer: V4(127.0.0.1:3434), socket: 1028 }

According to https://support.microsoft.com/en-us/help/929851/the-default-dynamic-port-range-for-tcp-ip-has-changed-in-windows-vista the dynamic port range is 1025 to 5000 inclusive, so the collision rate is ≈1/3976 per build if uniformly distributed.

[nnethercote]

I've seen this on my Linux box recently, so much so that I think it has become a permafail.