Panics cannot be caught on iOS

[arcln]

Bevy version

0.16

Relevant system information

iPhone 14 Pro Max, iOS 18.4.1 (real device)

What you did

I tried to catch all panics in my bevy app in order to send them to my monitoring infrastructure. It works on all platform but on iOS, a panic-in-panic happens which aborts the process, preventing me from sending the panic to the telemetry server.

std::panic::catch_unwind(|| {
    let mut app = App::new();
    app.add_plugins(DefaultPlugins);
    app.add_systems(Startup, || panic!("this is a test panic"));
    app.run();
});

What went wrong

• what were you expecting?

I was expecting my program to exit cleanly after the panic has been caught, just like it does on the other platforms I tested on (macOS and Android).

• what actually happened?

A panic-in-panic is happening somewhere in bevy. It results in an aborting panic, which cannot be caught by catch_unwind. Unfortunately the backtrace shows <unknown> for the interesting symbols.

thread '<unnamed>' panicked at crates/client/src/lib.rs:138:37:
this is a test panic
stack backtrace:
   0:        0x102448494 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hab422a1a11b8f7b3
   1:        0x102464520 - core::fmt::write::hfe39fe5ff3c4c688
   2:        0x10244558c - std::io::Write::write_fmt::h116d6e9d58f606e5
   3:        0x102448348 - std::sys::backtrace::BacktraceLock::print::h40b74fd903632aeb
   4:        0x102449390 - std::panicking::default_hook::{{closure}}::h9855a663cdb88002
   5:        0x1024491c8 - std::panicking::default_hook::hf18a76756aee275a
   6:        0x102449d4c - std::panicking::rust_panic_with_hook::h2883ee581935c57a
   7:        0x1024497e0 - std::panicking::begin_panic_handler::{{closure}}::h8936e4f587ecc2e6
   8:        0x102448948 - std::sys::backtrace::__rust_end_short_backtrace::h6cfbeafc1a5b28df
   9:        0x1024494c0 - _rust_begin_unwind
  10:        0x1024ff9b8 - core::panicking::panic_fmt::hb4f40d95ce1eb887
  11:        0x100ec88f0 - myapp_client::run::{{closure}}::{{closure}}::h964aa8b445c7e7e6
  12:        0x100ec07f8 - core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut::h09404907c1da7447
  13:        0x100ec01dc - <Func as bevy_ecs::system::function_system::SystemParamFunction<fn() .> Out>>::run::h12df91a2ec1e40d3
  14:        0x100ec0200 - <bevy_ecs::system::function_system::FunctionSystem<Marker,F> as bevy_ecs::system::system::System>::run_unsafe::h1fc51bcd1bcdc196
  15:        0x100ec02b4 - <bevy_ecs::system::schedule_system::InfallibleSystemWrapper<S> as bevy_ecs::system::system::System>::run_unsafe::h38ad07333b28653e
  16:        0x10239f204 - bevy_ecs::schedule::executor::__rust_begin_short_backtrace::run_unsafe::h733863d9ffafbf3c
  17:        0x10235f034 - <async_executor::AsyncCallOnDrop<Fut,Cleanup> as core::future::future::Future>::poll::h267a5c0fe8f26b89
  18:        0x102360ec8 - async_task::raw::RawTask<F,T,S,M>::run::hc264f35e34703ff4
  19:        0x1017d9638 - std::sys::backtrace::__rust_begin_short_backtrace::hae7a90c17f14a4a0
  20:        0x101800a68 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h5c8bc33c3d5c5274
  21:        0x10244c468 - std::sys::pal::unix::thread::Thread::new::thread_start::ha28f8bde96933fc0
  22:        0x228672afc - <unknown>
Encountered a panic in system `myapp_client::run::{{closure}}::{{closure}}`!
Encountered a panic in system `bevy_app::main_schedule::Main::run_main`!
thread '<unnamed>' panicked at library/core/src/panicking.rs:218:5:
panic in a function that cannot unwind
stack backtrace:
   0:        0x102448494 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hab422a1a11b8f7b3
   1:        0x102464520 - core::fmt::write::hfe39fe5ff3c4c688
   2:        0x10244558c - std::io::Write::write_fmt::h116d6e9d58f606e5
   3:        0x102448348 - std::sys::backtrace::BacktraceLock::print::h40b74fd903632aeb
   4:        0x102449390 - std::panicking::default_hook::{{closure}}::h9855a663cdb88002
   5:        0x1024491c8 - std::panicking::default_hook::hf18a76756aee275a
   6:        0x102449d4c - std::panicking::rust_panic_with_hook::h2883ee581935c57a
   7:        0x1024497e0 - std::panicking::begin_panic_handler::{{closure}}::h8936e4f587ecc2e6
   8:        0x102448948 - std::sys::backtrace::__rust_end_short_backtrace::h6cfbeafc1a5b28df
   9:        0x1024494c0 - _rust_begin_unwind
  10:        0x1024ff9ec - core::panicking::panic_nounwind_fmt::h10a8bb1d36d76fc7
  11:        0x1024ffa64 - core::panicking::panic_nounwind::h730843ac744ca085
  12:        0x1024ffb50 - core::panicking::panic_cannot_unwind::h81a758f0e2e788ae
  13:        0x100fd5744 - winit::platform_impl::ios::event_loop::setup_control_flow_observers::control_flow_main_end_handler::h19cf5123daf9cc31
  14:        0x19e1180e0 - <unknown>
  15:        0x19e117e80 - <unknown>
  16:        0x19e167ca4 - <unknown>
  17:        0x19e18c700 - <unknown>
  18:        0x1eaccd190 - <unknown>
  19:        0x1a0daa240 - <unknown>
  20:        0x1a0da8470 - <unknown>
  21:        0x100f71588 - winit::platform_impl::ios::event_loop::EventLoop<T>::run::h43d3193feda1c8d6
  22:        0x100f64184 - core::ops::function::FnOnce::call_once{{vtable.shim}}::hbeaf0d9d7dad3ec7
  23:        0x1023569ec - bevy_app::app::App::run::h500b5d24e766e6b7
  24:        0x100ec885c - myapp_client::run::hf83fbac4175e70fd
  25:        0x100ec00b8 - _start_app
  26:        0x100ec000c - _main
thread caused non-unwinding panic. aborting.

I would happily propose a fix, but I have no idea where to look for. Any pointers will be appreciated.