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Add error messages for the spooky insertions (#2581)
# Objective Sometimes, the unwraps in `entity_mut` could fail here, if the entity was despawned *before* this command was applied. The simplest case involves two command buffers: ```rust use bevy::prelude::*; fn b(mut commands1: Commands, mut commands2: Commands) { let id = commands2.spawn().insert_bundle(()).id(); commands1.entity(id).despawn(); } fn main() { App::build().add_system(b.system()).run(); } ``` However, a more complicated version arises in the case of ambiguity: ```rust use std::time::Duration; use bevy::{app::ScheduleRunnerPlugin, prelude::*}; use rand::Rng; fn cleanup(mut e: ResMut<Option<Entity>>) { *e = None; } fn sleep_randomly() { let mut rng = rand::thread_rng(); std:🧵:sleep(Duration::from_millis(rng.gen_range(0..50))); } fn spawn(mut commands: Commands, mut e: ResMut<Option<Entity>>) { *e = Some(commands.spawn().insert_bundle(()).id()); } fn despawn(mut commands: Commands, e: Res<Option<Entity>>) { let mut rng = rand::thread_rng(); std:🧵:sleep(Duration::from_millis(rng.gen_range(0..50))); if let Some(e) = *e { commands.entity(e).despawn(); } } fn main() { App::build() .add_system(cleanup.system().label("cleanup")) .add_system(sleep_randomly.system().label("before_despawn")) .add_system(despawn.system().after("cleanup").after("before_despawn")) .add_system(sleep_randomly.system().label("before_spawn")) .add_system(spawn.system().after("cleanup").after("before_spawn")) .insert_resource(None::<Entity>) .add_plugin(ScheduleRunnerPlugin::default()) .run(); } ``` In the cases where this example crashes, it's because `despawn` was ordered before `spawn` in the topological ordering of systems (which determines when buffers are applied). However, `despawn` actually ran *after* `spawn`, because these systems are ambiguous, so the jiggles in the sleeping time triggered a case where this works. ## Solution - Give a better error message
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2 changed files with 45 additions and 32 deletions
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@ -173,6 +173,7 @@ pub struct Entities {
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/// Once `flush()` is done, `free_cursor` will equal `pending.len()`.
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pending: Vec<u32>,
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free_cursor: AtomicI64,
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/// Stores the number of free entities for [`len`](Entities::len)
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len: u32,
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}
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@ -369,12 +370,12 @@ impl Entities {
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}
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}
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/// Returns true if the [`Entities`] contains [`entity`](Entity).
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// This will return false for entities which have been freed, even if
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// not reallocated since the generation is incremented in `free`
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pub fn contains(&self, entity: Entity) -> bool {
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// Note that out-of-range IDs are considered to be "contained" because
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// they must be reserved IDs that we haven't flushed yet.
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self.meta
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.get(entity.id as usize)
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.map_or(true, |meta| meta.generation == entity.generation)
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self.resolve_from_id(entity.id())
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.map_or(false, |e| e.generation() == entity.generation)
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}
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pub fn clear(&mut self) {
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@ -399,31 +400,23 @@ impl Entities {
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}
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}
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/// Panics if the given id would represent an index outside of `meta`.
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/// Get the [`Entity`] with a given id, if it exists in this [`Entities`] collection
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/// Returns `None` if this [`Entity`] is outside of the range of currently reserved Entities
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///
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/// # Safety
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///
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/// Must only be called for currently allocated `id`s.
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pub unsafe fn resolve_unknown_gen(&self, id: u32) -> Entity {
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let meta_len = self.meta.len();
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if meta_len > id as usize {
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let meta = &self.meta[id as usize];
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Entity {
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generation: meta.generation,
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id,
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}
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/// Note: This method may return [`Entities`](Entity) which are currently free
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/// Note that [`contains`](Entities::contains) will correctly return false for freed
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/// entities, since it checks the generation
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pub fn resolve_from_id(&self, id: u32) -> Option<Entity> {
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let idu = id as usize;
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if let Some(&EntityMeta { generation, .. }) = self.meta.get(idu) {
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Some(Entity { generation, id })
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} else {
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// See if it's pending, but not yet flushed.
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// `id` is outside of the meta list - check whether it is reserved but not yet flushed.
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let free_cursor = self.free_cursor.load(Ordering::Relaxed);
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let num_pending = std::cmp::max(-free_cursor, 0) as usize;
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if meta_len + num_pending > id as usize {
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// Pending entities will have generation 0.
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Entity { generation: 0, id }
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} else {
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panic!("entity id is out of range");
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}
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// If this entity was manually created, then free_cursor might be positive
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// Returning None handles that case correctly
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let num_pending = usize::try_from(-free_cursor).ok()?;
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(idu < self.meta.len() + num_pending).then(|| Entity { generation: 0, id })
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}
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}
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@ -508,7 +501,7 @@ impl EntityMeta {
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generation: 0,
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location: EntityLocation {
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archetype_id: ArchetypeId::INVALID,
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index: usize::max_value(), // dummy value, to be filled in
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index: usize::MAX, // dummy value, to be filled in
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},
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};
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}
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@ -6,7 +6,7 @@ use crate::{
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entity::{Entities, Entity},
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world::World,
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};
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use bevy_utils::tracing::{debug, error};
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use bevy_utils::tracing::{error, warn};
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pub use command_queue::CommandQueue;
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use std::marker::PhantomData;
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@ -144,7 +144,13 @@ impl<'w, 's> Commands<'w, 's> {
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/// }
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/// # example_system.system();
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/// ```
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#[track_caller]
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pub fn entity<'a>(&'a mut self, entity: Entity) -> EntityCommands<'w, 's, 'a> {
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assert!(
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self.entities.contains(entity),
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"Attempting to create an EntityCommands for entity {:?}, which doesn't exist.",
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entity
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);
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EntityCommands {
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entity,
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commands: self,
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@ -371,7 +377,9 @@ pub struct Despawn {
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impl Command for Despawn {
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fn write(self, world: &mut World) {
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if !world.despawn(self.entity) {
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debug!("Failed to despawn non-existent entity {:?}", self.entity);
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warn!("Could not despawn entity {:?} because it doesn't exist in this World.\n\
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If this command was added to a newly spawned entity, ensure that you have not despawned that entity within the same stage.\n\
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This may have occurred due to system order ambiguity, or if the spawning system has multiple command buffers", self.entity);
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}
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}
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}
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@ -386,7 +394,13 @@ where
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T: Bundle + 'static,
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{
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fn write(self, world: &mut World) {
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world.entity_mut(self.entity).insert_bundle(self.bundle);
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if let Some(mut entity) = world.get_entity_mut(self.entity) {
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entity.insert_bundle(self.bundle);
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} else {
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panic!("Could not insert a bundle (of type `{}`) for entity {:?} because it doesn't exist in this World.\n\
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If this command was added to a newly spawned entity, ensure that you have not despawned that entity within the same stage.\n\
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This may have occurred due to system order ambiguity, or if the spawning system has multiple command buffers", std::any::type_name::<T>(), self.entity);
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}
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}
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}
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@ -401,7 +415,13 @@ where
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T: Component,
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{
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fn write(self, world: &mut World) {
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world.entity_mut(self.entity).insert(self.component);
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if let Some(mut entity) = world.get_entity_mut(self.entity) {
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entity.insert(self.component);
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} else {
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panic!("Could not add a component (of type `{}`) to entity {:?} because it doesn't exist in this World.\n\
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If this command was added to a newly spawned entity, ensure that you have not despawned that entity within the same stage.\n\
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This may have occurred due to system order ambiguity, or if the spawning system has multiple command buffers", std::any::type_name::<T>(), self.entity);
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}
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}
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}
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