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Fix unsoundness in QueryState::is_empty #9463

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Sep 3, 2023
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34 changes: 32 additions & 2 deletions crates/bevy_ecs/src/query/state.rs
Original file line number Diff line number Diff line change
Expand Up @@ -128,12 +128,42 @@ impl<Q: WorldQuery, F: ReadOnlyWorldQuery> QueryState<Q, F> {
}

/// Checks if the query is empty for the given [`World`], where the last change and current tick are given.
///
/// # Panics
///
/// If `world` does not match the one used to call `QueryState::new` for this instance.
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#[inline]
pub fn is_empty(&self, world: &World, last_run: Tick, this_run: Tick) -> bool {
// SAFETY: NopFetch does not access any members while &self ensures no one has exclusive access
self.validate_world(world.id());
// SAFETY: The world has been validated.
unsafe {
self.is_empty_unsafe_world_cell(
world.as_unsafe_world_cell_readonly(),
last_run,
this_run,
)
}
}

/// Checks if the query is empty for the given [`UnsafeWorldCell`].
///
/// # Safety
///
/// `world` must match the one used to create this [`QueryState`].
#[inline]
pub(crate) unsafe fn is_empty_unsafe_world_cell(
&self,
world: UnsafeWorldCell,
last_run: Tick,
this_run: Tick,
) -> bool {
// SAFETY:
// - `as_nop()` ensures no world data is accessed.
// - `&self` ensures no one has exclusive access.
// - Caller ensures that the world matches.
unsafe {
self.as_nop()
.iter_unchecked_manual(world.as_unsafe_world_cell_readonly(), last_run, this_run)
.iter_unchecked_manual(world, last_run, this_run)
.next()
.is_none()
}
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11 changes: 5 additions & 6 deletions crates/bevy_ecs/src/system/query.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1366,12 +1366,11 @@ impl<'w, 's, Q: WorldQuery, F: ReadOnlyWorldQuery> Query<'w, 's, Q, F> {
/// ```
#[inline]
pub fn is_empty(&self) -> bool {
self.state.is_empty(
// SAFETY: `QueryState::is_empty` does not access world data.
unsafe { self.world.unsafe_world() },
self.last_run,
self.this_run,
)
// SAFETY: `self.world` matches `self.state`.
unsafe {
self.state
.is_empty_unsafe_world_cell(self.world, self.last_run, self.this_run)
}
}

/// Returns `true` if the given [`Entity`] matches the query.
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