report a command system origin in case of panic

Cargo.toml

@@ -52,6 +52,8 @@ trace_chrome = ["bevy_internal/trace_chrome"]
 trace = ["bevy_internal/trace"]
 wgpu_trace = ["bevy_internal/wgpu_trace"]
 
+bevy_command_panic_origin = ["bevy_internal/bevy_command_panic_origin"]
+
 # Image format support for texture loading (PNG and HDR are enabled by default)
 hdr = ["bevy_internal/hdr"]
 png = ["bevy_internal/png"]

crates/bevy_ecs/Cargo.toml

@@ -15,6 +15,7 @@ categories = ["game-engines", "data-structures"]
 
 [features]
 trace = []
+command_panic_origin = []
 default = ["bevy_reflect"]
 
 [dependencies]

crates/bevy_ecs/src/system/commands.rs

@@ -5,7 +5,14 @@ use crate::{
     world::World,
 };
 use bevy_utils::tracing::debug;
+#[cfg(feature = "command_panic_origin")]
+use bevy_utils::tracing::error;
 use std::marker::PhantomData;
+#[cfg(feature = "command_panic_origin")]
+use std::{
+    borrow::Cow,
+    panic::{self, AssertUnwindSafe},
+};
 
 /// A [`World`] mutation.
 pub trait Command: Send + Sync + 'static {
@@ -15,7 +22,9 @@ pub trait Command: Send + Sync + 'static {
 /// A queue of [`Command`]s.
 #[derive(Default)]
 pub struct CommandQueue {
-    commands: Vec<Box<dyn Command>>,
+    pub(crate) commands: Vec<Box<dyn Command>>,
+    #[cfg(feature = "command_panic_origin")]
+    pub(crate) system_name: Option<Cow<'static, str>>,
 }
 
 impl CommandQueue {
@@ -24,7 +33,22 @@ impl CommandQueue {
     pub fn apply(&mut self, world: &mut World) {
         world.flush();
         for command in self.commands.drain(..) {
+            // TODO: replace feature by proper error handling from commands
+            // https://github.com/bevyengine/bevy/issues/2004
+            #[cfg(not(feature = "command_panic_origin"))]
             command.write(world);
+            #[cfg(feature = "command_panic_origin")]
+            {
+                let may_panic = panic::catch_unwind(AssertUnwindSafe(|| {
+                    command.write(world);
+                }));
+                if may_panic.is_err() {
+                    if let Some(system_name) = &self.system_name {
+                        error!("panic while applying a command from {}", system_name);
+                    }
+                    panic!("panic applying a command");
+                }
+            }
         }
     }
 

crates/bevy_ecs/src/system/into_system.rs

@@ -47,6 +47,11 @@ impl SystemState {
     pub fn set_non_send(&mut self) {
         self.is_send = false;
     }
+
+    #[cfg(feature = "command_panic_origin")]
+    pub fn name(&self) -> Cow<'static, str> {
+        self.name.clone()
+    }
 }
 
 /// Conversion trait to turn something into a [`System`].

crates/bevy_ecs/src/system/system_param.rs

@@ -529,8 +529,13 @@ impl<'a> SystemParam for Commands<'a> {
 unsafe impl SystemParamState for CommandQueue {
     type Config = ();
 
-    fn init(_world: &mut World, _system_state: &mut SystemState, _config: Self::Config) -> Self {
-        Default::default()
+    #[allow(unused)]
+    fn init(_world: &mut World, system_state: &mut SystemState, _config: Self::Config) -> Self {
+        CommandQueue {
+            #[cfg(feature = "command_panic_origin")]
+            system_name: Some(system_state.name()),
+            ..Default::default()
+        }
     }
 
     fn apply(&mut self, world: &mut World) {

crates/bevy_internal/Cargo.toml

@@ -41,6 +41,9 @@ x11 = ["bevy_winit/x11"]
 # enable rendering of font glyphs using subpixel accuracy
 subpixel_glyph_atlas = ["bevy_text/subpixel_glyph_atlas"]
 
+# enable tracing system origin of commands in case of command failure
+bevy_command_panic_origin = ["bevy_ecs/command_panic_origin"]
+
 # enable systems that allow for automated testing on CI
 bevy_ci_testing = ["bevy_app/bevy_ci_testing"]