Add bypass_change_detection method

crates/bevy_ecs/src/change_detection.rs

@@ -43,6 +43,11 @@ pub const MAX_CHANGE_AGE: u32 = u32::MAX - (2 * CHECK_TICK_THRESHOLD - 1);
 /// ```
 ///
 pub trait DetectChanges {
+ /// The type contained within this smart pointer
+ ///
+ /// For example, for `Res<T>` this would be `T`.
+ type Inner;
+
  /// Returns `true` if this value was added after the system last ran.
  fn is_added(&self) -> bool;
 
@@ -73,11 +78,21 @@ pub trait DetectChanges {
  /// If you merely want to flag this data as changed, use [`set_changed`](DetectChanges::set_changed) instead.
  /// If you want to avoid triggering change detection, use [`bypass_change_detection`](DetectChanges::bypass_change_detection) instead.
  fn set_last_changed(&mut self, last_change_tick: u32);
+
+ /// Manually bypasses change detection, allowing you to mutate the underlying value without updating the change tick.
+ ///
+ /// This is a risky operation, that can have unexpected consequences on any system relying on this code.
+ /// However, it can be an essential escape hatch when, for example,
+ /// you are trying to synchronize representations using change detection and need to avoid infinite recursion.
+ fn bypass_change_detection(&mut self) -> &mut Self::Inner;
 }
 
 macro_rules! change_detection_impl {
  ($name:ident < $( $generics:tt ),+ >, $target:ty, $($traits:ident)?) => {
  impl<$($generics),* $(: $traits)?> DetectChanges for $name<$($generics),*> {
+ // FIXME: this is requesting *all* generics, I just want the first generic type
+ type Inner = $generics;
+
  #[inline]
  fn is_added(&self) -> bool {
  self.ticks
@@ -108,6 +123,11 @@ macro_rules! change_detection_impl {
  fn set_last_changed(&mut self, last_change_tick: u32) {
  self.ticks.last_change_tick = last_change_tick
  }
+
+ #[inline]
+ fn bypass_change_detection(&mut self) -> &mut Self::Inner {
+ self.value
+ }
  }
 
  impl<$($generics),* $(: $traits)?> Deref for $name<$($generics),*> {
@@ -268,12 +288,15 @@ impl<'a> MutUntyped<'a> {
  /// Returns the pointer to the value, without marking it as changed.
  ///
  /// In order to mark the value as changed, you need to call [`set_changed`](DetectChanges::set_changed) manually.
+ #[inline]
  pub fn into_inner(self) -> PtrMut<'a> {
  self.value
  }
 }
 
-impl DetectChanges for MutUntyped<'_> {
+impl<'a> DetectChanges for MutUntyped<'a> {
+ type Inner = PtrMut<'a>;
+
  fn is_added(&self) -> bool {
  self.ticks
  .component_ticks
@@ -300,6 +323,10 @@ impl DetectChanges for MutUntyped<'_> {
  fn set_last_changed(&mut self, last_change_tick: u32) {
  self.ticks.last_change_tick = last_change_tick
  }
+
+ fn bypass_change_detection(&mut self) -> &mut Self::Inner {
+ &mut self.into_inner()
+ }
 }
 
 impl std::fmt::Debug for MutUntyped<'_> {