Crash when DISPLAY is unset

[eras]

I wrote https://github.com/eras/ClickMuteJack/ using this and noticed that it crashes if I start it with an empty DISPLAY:

% DISPLAY= target/debug/click_mute
Loaded config from click_mute.ini
XOpenDisplay() failed!

zsh: segmentation fault  DISPLAY= target/debug/click_mute

Doesn't seem like there's a way to handle this problem in user code.

Similar crash happens with non-empty DISPLAY but no permission for the server, which is how I noticed this issue in the first place. The gui code is here: https://github.com/eras/ClickMuteJack/blob/master/src/gui.rs

[eras]

gdb backtrace:

XOpenDisplay() failed!


Thread 2 "click_mute" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff66f2700 (LWP 3588334)]
0x00005555556df887 in <std::ffi::c_str::CString as core::ops::drop::Drop>::drop (
    self=0x7ffff66f0e88)
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/ffi/c_str.rs:770
770	/rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/ffi/c_str.rs: No such file or directory.
(gdb) bt
#0  0x00005555556df887 in <std::ffi::c_str::CString as core::ops::drop::Drop>::drop (
    self=0x7ffff66f0e88)
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/ffi/c_str.rs:770
#1  0x00005555556da553 in core::ptr::drop_in_place<std::ffi::c_str::CString> ()
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/core/src/ptr/mod.rs:192
#2  0x00005555556d4da5 in sapp_linux::_sapp_fail (
    msg=0x5555559496f3 "XOpenDisplay() failed!\n")
    at /home/flux/.cargo/registry/src/github.com-1ecc6299db9ec823/sapp-linux-0.1.12/src/lib.rs:1150
#3  0x00005555556d7bd0 in sapp_linux::sapp_run (desc=0x7ffff66f10d8)
    at /home/flux/.cargo/registry/src/github.com-1ecc6299db9ec823/sapp-linux-0.1.12/src/lib.rs:2731
#4  0x00005555555e363e in miniquad::start (conf=..., f=...)
    at /home/flux/.cargo/registry/src/github.com-1ecc6299db9ec823/miniquad-0.3.0-alpha.30/src/lib.rs:432
#5  0x0000555555604369 in click_mute::gui::main (quit=..., click_info=..., config=..., 
    control=...) at src/gui.rs:389
#6  0x000055555561d7e6 in click_mute::main::{{closure}} () at src/main.rs:40
#7  0x00005555555df770 in std::sys_common::backtrace::__rust_begin_short_backtrace (
    f=...)
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/sys_common/backtrace.rs:125
#8  0x0000555555626a2c in std::thread::Builder::spawn_unchecked::{{closure}}::{{closure}} () at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/thread/mod.rs:481
#9  0x00005555555da2b0 in <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once (self=..., _args=())
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/panic.rs:346
#10 0x000055555561c967 in std::panicking::try::do_call (
    data=0x7ffff66f1b68 "\300\205\266UUU\000")
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/panicking.rs:401
#11 0x000055555561cc0d in __rust_try ()
#12 0x000055555561c6c1 in std::panicking::try (f=...)
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/panicking.rs:365
#13 0x00005555555da370 in std::panic::catch_unwind (f=...)
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/panic.rs:433
#14 0x00005555556264bc in std::thread::Builder::spawn_unchecked::{{closure}} ()
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/std/src/thread/mod.rs:480
#15 0x00005555555fa2ce in core::ops::function::FnOnce::call_once{{vtable-shim}} ()
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/core/src/ops/function.rs:227
#16 0x000055555591b727 in <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once ()
    at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/alloc/src/boxed.rs:1575
--Type <RET> for more, q to quit, c to continue without paging--c
#17 <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once () at /rustc/3e99439f4dacc8ba0d2ca48d221694362d587927/library/alloc/src/boxed.rs:1575
#18 std::sys::unix::thread::Thread::new::thread_start () at library/std/src/sys/unix/thread.rs:71
#19 0x00007ffff7b1efa3 in start_thread (arg=<optimized out>) at pthread_create.c:486
#20 0x00007ffff78cc4cf in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb) 

[not-fl3]

What is the expected behavior here? No DISPLAY means no X server running and miniquad depends on X
Any other X apps do not work without DISPLAY either:

> DISPLAY= xterm
xterm: Xt error: Can't open display: 
xterm: DISPLAY is not set

[not-fl3]

Made a small fix and now it properly exits without a segfault: not-fl3/miniquad#208
It would be better if miniquad::start would return an error instead of just exit(0), so lets keep this issue open