Fix bug in event broadcasting

When a component is added or removed from an entity, the system list
currently being iterated over may no longer match the target entity.
To fix this, events are now only handled once the current event has
finished broadcasting. Still not entirely sure that this is the most
desirable behavior though.

The `EventPtr` and `EventMut` interface also had an update.

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Change Log
 
+## Unreleased
+
+- Fixed a bug in event propagation.
+- The behavior of the event queue has changed. The next event in the queue is handled only once the current event has finished broadcasting.
+- Changed `EventPtr` interface and relaxed `Send` and `Sync` bounds for `EventMut`.
+
 ## 0.2.2 - 2024-02-8
 
 - Update documentation

README.md

@@ -7,11 +7,11 @@ It aims to have a small but maximally expressive set of features that are easy a
 
 ## Features
 
-- In addition to the usual Entities, Components, and Systems, `evenio` introduces _events_ as a first-class citizen.
-Rather than restricting systems to run once every frame/update in a fixed order, systems are generalized as _event handlers_.
+- In addition to the usual Entities, Components, and Systems, `evenio` introduces events as a first-class citizen.
+Rather than restricting systems to run once every frame/update in a fixed order, systems are generalized as event handlers.
 The control flow of the entire program is then defined by the flow of events between systems.
 - Structural changes to the world (such as entity despawning, component additions/removals, etc.) are mediated by events, allowing systems to hook into their occurrence.
-- _Targeted events_ enable systems to efficiently filter events based on queries.
+- Targeted events enable systems to efficiently filter events based on queries.
 - Component types, event types, and systems are identified with generational indices, allowing them to be added and removed dynamically.
 - Execute systems in parallel with [Rayon].
 - Core of the library does not depend on Rust's type system.

src/assert.rs

@@ -1,7 +1,7 @@
 //! Utilities for runtime and compile-time assertions.
 
-use alloc::vec::Vec;
 use core::marker::PhantomData;
+use core::slice::SliceIndex;
 use core::{fmt, mem};
 
 use slab::Slab;
@@ -16,7 +16,7 @@ const _: () = assert!(
 
 /// Extension trait for checked array indexing with checks removed in release
 /// mode.
-pub(crate) trait GetDebugChecked {
+pub(crate) trait GetDebugChecked<Idx> {
     type Output: ?Sized;
 
     /// Gets a reference to the element at the given index.
@@ -28,7 +28,7 @@ pub(crate) trait GetDebugChecked {
     ///
     /// - `idx` must be in bounds.
     #[track_caller]
-    unsafe fn get_debug_checked(&self, idx: usize) -> &Self::Output;
+    unsafe fn get_debug_checked(&self, idx: Idx) -> &Self::Output;
     /// Gets a mutable reference to the element at the given index.
     ///
     /// If `idx` is not in bounds, a panic occurs in debug mode and Undefined
@@ -38,23 +38,24 @@ pub(crate) trait GetDebugChecked {
     ///
     /// - `idx` must be in bounds.
     #[track_caller]
-    unsafe fn get_debug_checked_mut(&mut self, idx: usize) -> &mut Self::Output;
+    unsafe fn get_debug_checked_mut(&mut self, idx: Idx) -> &mut Self::Output;
 }
 
-impl<T> GetDebugChecked for [T] {
-    type Output = T;
+impl<T, I> GetDebugChecked<I> for [T]
+where
+    I: SliceIndex<[T]>,
+{
+    type Output = I::Output;
 
-    #[inline]
-    unsafe fn get_debug_checked(&self, idx: usize) -> &Self::Output {
+    unsafe fn get_debug_checked(&self, idx: I) -> &Self::Output {
         #[cfg(debug_assertions)]
         return &self[idx];
 
         #[cfg(not(debug_assertions))]
         return self.get_unchecked(idx);
     }
 
-    #[inline]
-    unsafe fn get_debug_checked_mut(&mut self, idx: usize) -> &mut Self::Output {
+    unsafe fn get_debug_checked_mut(&mut self, idx: I) -> &mut Self::Output {
         #[cfg(debug_assertions)]
         return &mut self[idx];
 
@@ -63,22 +64,8 @@ impl<T> GetDebugChecked for [T] {
     }
 }
 
-impl<T> GetDebugChecked for Vec<T> {
-    type Output = T;
-
-    #[inline]
-    unsafe fn get_debug_checked(&self, idx: usize) -> &Self::Output {
-        self.as_slice().get_debug_checked(idx)
-    }
-
-    #[inline]
-    unsafe fn get_debug_checked_mut(&mut self, idx: usize) -> &mut Self::Output {
-        self.as_mut_slice().get_debug_checked_mut(idx)
-    }
-}
-
 // Don't use `Slab::get_unchecked` because there's a panicking branch. https://github.com/tokio-rs/slab/pull/74
-impl<T> GetDebugChecked for Slab<T> {
+impl<T> GetDebugChecked<usize> for Slab<T> {
     type Output = T;
 
     #[inline]

src/blob_vec.rs

@@ -27,9 +27,6 @@ impl BlobVec {
     /// - `drop` must be safe to call with elements of this `BlobVec` as
     ///   described by [`DropFn`]'s documentation.
     pub(crate) unsafe fn new(layout: Layout, drop: DropFn) -> Self {
-        // // SAFETY: `Layout` guarantees alignment is non-zero.
-        // let data = NonNull::new(layout.align() as *mut u8).unwrap_debug_checked();
-
         Self {
             elem_layout: pad_to_align(&layout),
             len: 0,