From 9d13ae3113c508cb66b533641fd02127ef01dca4 Mon Sep 17 00:00:00 2001
From: SpecificProtagonist <specificprotagonist@posteo.org>
Date: Sat, 24 Feb 2024 10:52:25 +0100
Subject: [PATCH] Fix SimpleExecutor crash (#12076)

# Objective

Since #9822, `SimpleExecutor` panics when an automatic sync point is
inserted:

```rust
let mut sched = Schedule::default();
sched.set_executor_kind(ExecutorKind::Simple);
sched.add_systems((|_: Commands| (), || ()).chain());
sched.run(&mut World::new());
```
```
System's param_state was not found. Did you forget to initialize this system before running it?
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Encountered a panic in system `bevy_ecs::schedule::executor::apply_deferred`!
```

## Solution

Don't try to run the `apply_deferred` system.
---
 .../bevy_ecs/src/schedule/executor/simple.rs  | 21 ++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/crates/bevy_ecs/src/schedule/executor/simple.rs b/crates/bevy_ecs/src/schedule/executor/simple.rs
index 002ba532ad..6c1b7437ac 100644
--- a/crates/bevy_ecs/src/schedule/executor/simple.rs
+++ b/crates/bevy_ecs/src/schedule/executor/simple.rs
@@ -4,7 +4,9 @@ use fixedbitset::FixedBitSet;
 use std::panic::AssertUnwindSafe;
 
 use crate::{
-    schedule::{BoxedCondition, ExecutorKind, SystemExecutor, SystemSchedule},
+    schedule::{
+        executor::is_apply_deferred, BoxedCondition, ExecutorKind, SystemExecutor, SystemSchedule,
+    },
     world::World,
 };
 
@@ -86,6 +88,10 @@ impl SystemExecutor for SimpleExecutor {
             }
 
             let system = &mut schedule.systems[system_index];
+            if is_apply_deferred(system) {
+                continue;
+            }
+
             let res = std::panic::catch_unwind(AssertUnwindSafe(|| {
                 system.run((), world);
             }));
@@ -125,3 +131,16 @@ fn evaluate_and_fold_conditions(conditions: &mut [BoxedCondition], world: &mut W
         .map(|condition| condition.run((), world))
         .fold(true, |acc, res| acc && res)
 }
+
+#[cfg(test)]
+#[test]
+fn skip_automatic_sync_points() {
+    // Schedules automatically insert appy_deferred systems, but these should
+    // not be executed as they only serve as markers and are not initialized
+    use crate::prelude::*;
+    let mut sched = Schedule::default();
+    sched.set_executor_kind(ExecutorKind::Simple);
+    sched.add_systems((|_: Commands| (), || ()).chain());
+    let mut world = World::new();
+    sched.run(&mut world);
+}