Thread panic message to stderr kills windowed mode Windows binaries

[rsaarelm]

Windows binaries built with the -mwindows linker flag can't have any output to stdout or stderr in them or Windows will instantly terminate the program. I want to have windowed mode binaries for GUI applications, since without the windowed mode flag the binary will spawn a visible console window in addition to the GUI window every time it's run.

Panicing threads seem to cause an unconditional print to stderr. I'm trying to write a panic handler that will pop up a Windows message dialog instead of printing to stdout when the program terminates with a panic, but currently can't do that because windowed mode programs die at the point of the panic and the handler is never reached.

To test this, write panic.rs:

fn f() { panic!("This kills the Windows"); }

fn main() {
    match std::thread::Builder::new().spawn(f).unwrap().join() {
        Err(_) => { std::fs::File::create("panic_log.txt"); }
        _ => {}
    }
}

Build it with rustc -C link-args=-mwindows panic.rs. Then run panic.exe from the Windows explorer. The program terminates and the panic_log.txt file never shows up. (It does seem to work if you run it from the Command Prompt, but end users will be clicking an icon.)

[nagisa]

#24099

[Diggsey]

rust-lang/rfcs#1100

[retep998]

rust-lang/rfcs#1014 would fix this issue.

[alexcrichton]

The linked issues by @nagisa, @Diggsey, and @retep998 I believe all cover our bases pretty well here, so I'm going to close this as a dupe of them. Thanks regardless for the report though!