Panic + abort when overriding property list on `MeshLibrary`

[CenTdemeern1]

The following code hard crashes the editor when added to a GridMap:

use godot::{
    classes::{IMeshLibrary, MeshLibrary},
    prelude::*,
    register::info::PropertyInfo,
};

#[derive(GodotClass)]
#[class(base=MeshLibrary, init, tool)]
pub struct CrashingMeshLibrary {
    base: Base<MeshLibrary>,
}

#[godot_api]
impl IMeshLibrary for CrashingMeshLibrary {
    fn on_get_property_list(&mut self) -> Vec<PropertyInfo> {
        vec![]
    }
}

...but only when it's in a submodule, or something...? This bug is kind of weird and tends to disappear when studied

I can reproduce it with the following project when launching Godot via the command line:
reset; RUST_BACKTRACE=1 ./Godot /Users/centdemeern1/Documents/GodotProjects/meshlibrary-repro/Godot/project.godot
meshlibrary-repro.zip

Log and backtrace

Initialize godot-rust (API v4.7.stable.official, runtime v4.7.1.stable.official, safeguards strict)
Godot Engine v4.7.1.stable.official.a13da4feb - https://godotengine.org
Metal 4.0 - Forward+ - Using Device #0: Apple - Apple M4 (Apple9)


[backtrace of previous `bind_mut` borrow]
   0: std::backtrace_rs::backtrace::libunwind::trace
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/../../backtrace/src/backtrace/libunwind.rs:117:9
   1: std::backtrace_rs::backtrace::trace_unsynchronized::<<std::backtrace::Backtrace>::create::{closure#0}>
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/../../backtrace/src/backtrace/mod.rs:66:14
   2: <std::backtrace::Backtrace>::create
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/backtrace.rs:331:13
   3: <godot_core::storage::borrow_info::DebugBorrowTracker>::track_mut_borrow
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/mod.rs:175:28
   4: <godot_core::storage::single_threaded::InstanceStorage<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary> as godot_core::storage::instance_storage::Storage>::get_mut
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/single_threaded.rs:78:29
   5: <godot_core::storage::instance_storage::RecvMut as godot_core::storage::instance_storage::IntoVirtualMethodReceiver<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary>>::instance
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/instance_storage.rs:213:60
   6: godot_core::registry::callbacks::get_property_list::<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary>
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/registry/callbacks.rs:352:20


[panic /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/mod.rs:38]
  Gd<T>::bind_mut() failed, already bound; T = meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary.
    Make sure to use `self.base_mut()` instead of `self.to_gd()` when possible.
    Details: cannot borrow while accessible mutable borrow exists.

[panic backtrace]
   0: std::backtrace_rs::backtrace::libunwind::trace
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/../../backtrace/src/backtrace/libunwind.rs:117:9
   1: std::backtrace_rs::backtrace::trace_unsynchronized::<<std::backtrace::Backtrace>::create::{closure#0}>
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/../../backtrace/src/backtrace/mod.rs:66:14
   2: <std::backtrace::Backtrace>::create
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/backtrace.rs:331:13
   3: godot_core::private::set_gdext_hook::<godot_core::init::__gdext_load_library<meshlibrary_repro::ReproExtension>::{closure#0}::{closure#0}>::{closure#0}
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/private.rs:310:44
   4: <alloc::boxed::Box<dyn for<'a, 'b> core::ops::function::Fn<(&'a std::panic::PanicHookInfo<'b>,), Output = ()> + core::marker::Sync + core::marker::Send> as core::ops::function::Fn<(&std::panic::PanicHookInfo,)>>::call
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/alloc/src/boxed.rs:2289:9
   5: std::panicking::panic_with_hook
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/panicking.rs:833:13
   6: std::panicking::panic_handler::{closure#0}
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/panicking.rs:698:13
   7: std::sys::backtrace::__rust_end_short_backtrace::<std::panicking::panic_handler::{closure#0}, !>
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/sys/backtrace.rs:182:18
   8: __rustc::rust_begin_unwind
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/panicking.rs:689:5
   9: core::panicking::panic_fmt
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/core/src/panicking.rs:80:14
  10: godot_core::storage::bind_mut_failed::<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary>
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/mod.rs:38:5
  11: <godot_core::storage::single_threaded::InstanceStorage<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary> as godot_core::storage::instance_storage::Storage>::get_mut::{closure#0}
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/single_threaded.rs:76:33
  12: <core::result::Result<godot_cell::guards::MutGuard<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary>, alloc::boxed::Box<dyn core::error::Error>>>::unwrap_or_else::<<godot_core::storage::single_threaded::InstanceStorage<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary> as godot_core::storage::instance_storage::Storage>::get_mut::{closure#0}>
             at /Users/centdemeern1/.rustup/toolchains/stable-aarch64-apple-darwin/lib/rustlib/src/rust/library/core/src/result.rs:1622:23
  13: <godot_core::storage::single_threaded::InstanceStorage<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary> as godot_core::storage::instance_storage::Storage>::get_mut
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/single_threaded.rs:76:14
  14: <godot_core::storage::instance_storage::RecvMut as godot_core::storage::instance_storage::IntoVirtualMethodReceiver<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary>>::instance
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/storage/instance_storage.rs:213:60
  15: godot_core::registry::callbacks::get_property_list::<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary>
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/registry/callbacks.rs:352:20


[panic /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/core/src/panicking.rs:225]  panic in a function that cannot unwind

[panic backtrace]
   0: std::backtrace_rs::backtrace::libunwind::trace
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/../../backtrace/src/backtrace/libunwind.rs:117:9
   1: std::backtrace_rs::backtrace::trace_unsynchronized::<<std::backtrace::Backtrace>::create::{closure#0}>
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/../../backtrace/src/backtrace/mod.rs:66:14
   2: <std::backtrace::Backtrace>::create
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/backtrace.rs:331:13
   3: godot_core::private::set_gdext_hook::<godot_core::init::__gdext_load_library<meshlibrary_repro::ReproExtension>::{closure#0}::{closure#0}>::{closure#0}
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/private.rs:310:44
   4: <alloc::boxed::Box<dyn for<'a, 'b> core::ops::function::Fn<(&'a std::panic::PanicHookInfo<'b>,), Output = ()> + core::marker::Sync + core::marker::Send> as core::ops::function::Fn<(&std::panic::PanicHookInfo,)>>::call
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/alloc/src/boxed.rs:2289:9
   5: std::panicking::panic_with_hook
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/panicking.rs:833:13
   6: std::panicking::panic_handler::{closure#0}
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/panicking.rs:691:13
   7: std::sys::backtrace::__rust_end_short_backtrace::<std::panicking::panic_handler::{closure#0}, !>
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/sys/backtrace.rs:182:18
   8: __rustc::rust_begin_unwind
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/std/src/panicking.rs:689:5
   9: core::panicking::panic_nounwind_fmt::runtime
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/core/src/panicking.rs:122:22
  10: core::panicking::panic_nounwind_fmt
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/core/src/intrinsics/mod.rs:2450:9
  11: core::panicking::panic_nounwind
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/core/src/panicking.rs:225:5
  12: core::panicking::panic_cannot_unwind
             at /rustc/8bab26f4f68e0e26f0bb7960be334d5b520ea452/library/core/src/panicking.rs:337:5
  13: godot_core::registry::callbacks::get_property_list::<meshlibrary_repro::module::crashing_meshlibrary::CrashingMeshLibrary>
             at /Users/centdemeern1/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/godot-core-0.5.4/src/registry/callbacks.rs:346:1


thread caused non-unwinding panic. aborting.
zsh: abort      RUST_BACKTRACE=1 ./Godot

[Bromeon]

As written on Discord, please don't provide entire projects (zip) but minimal examples. I know this means more work for you, but the alternative is that one of the few maintainers has to do this work, and we're not familiar with your setup and there are plenty of other open issues. Thanks 🙂

Very likely, you call a method from Rust that triggers on_get_property_list() callback, but don't make the &mut available again. Maybe just get_property_list or something else... With this information, can you try to locate the place that does so? Stacktrace could help here.

Then the 2nd problem is that the panic cannot unwind -- maybe a callback that is directly FFI-facing and doesn't catch panics 🤔 we should investigate this.

Btw, there is #1427 which looks similar and is caused by multithreaded access, not sure if that also is the case here.

[CenTdemeern1]

As written on Discord, please don't provide entire projects (zip) but minimal examples.

The attached project is a minimal example. It includes nothing except for the required repro setup (from my testing, I could not get it working with less; for some reason i could not get it to work without nesting that one rust module)
The only non-required files are probably icon.png and Cargo.lock
It's not the same zip I was gonna send you on Discord.

File list

Godot/meshlibrary-repro.gdextension.uid
Godot/meshlibrary-repro.gdextension
Godot/icon.svg
Godot/icon.svg.import
Godot/project.godot
Rust/Cargo.toml
Rust/Cargo.lock
Rust/src/lib.rs
Rust/src/module/crashing_meshlibrary.rs
Rust/src/module/mod.rs

Very likely, you call a method from Rust that triggers on_get_property_list() callback, but don't make the &mut available again.
Maybe just get_property_list or something else... With this information, can you try to locate the place that does so? Stacktrace could help here.

I'm not manually calling this method; I attached the backtrace to the initial comment though if you want to see it.
The engine seems to be calling get_property_list twice at the same time (from different threads maybe?)
I actually just tried enabling the experimental-threads feature and I haven't been able to reproduce this problem yet with it enabled.

Then the 2nd problem is that the panic cannot unwind -- maybe a callback that is directly FFI-facing and doesn't catch panics 🤔 we should investigate this.

Yeah, the backtrace says that godot_core::registry::callbacks::get_property_list at registry/callbacks.rs:346:1 can't unwind

Btw, there is #1427 which looks similar and is caused by multithreaded access, not sure if that also is the case here.

Sounds familiar, yeah...