13e89a1678
# Objective #19047 added an `MaybeUninit` field to `EntityMeta`, but did not guarantee that it will be initialized before access: ```rust let mut world = World::new(); let id = world.entities().reserve_entity(); world.flush(); world.entity(id); ``` <details> <summary>Miri Error</summary> ``` error: Undefined Behavior: using uninitialized data, but this operation requires initialized memory --> /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/entity/mod.rs:1121:26 | 1121 | unsafe { meta.spawned_or_despawned.assume_init() } | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ using uninitialized data, but this operation requires initialized memory | = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information = note: BACKTRACE: = note: inside closure at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/entity/mod.rs:1121:26: 1121:65 = note: inside `std::option::Option::<&bevy_ecs::entity::EntityMeta>::map::<bevy_ecs::entity::SpawnedOrDespawned, {closure@bevy_ecs::entity::Entities::entity_get_spawned_or_despawned::{closure#1}}>` at /home/vj/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:1144:29: 1144:33 = note: inside `bevy_ecs::entity::Entities::entity_get_spawned_or_despawned` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/entity/mod.rs:1112:9: 1122:15 = note: inside closure at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/entity/mod.rs:1094:13: 1094:57 = note: inside `bevy_ecs::change_detection::MaybeLocation::<std::option::Option<&std::panic::Location<'_>>>::new_with_flattened::<{closure@bevy_ecs::entity::Entities::entity_get_spawned_or_despawned_by::{closure#0}}>` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/change_detection.rs:1371:20: 1371:24 = note: inside `bevy_ecs::entity::Entities::entity_get_spawned_or_despawned_by` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/entity/mod.rs:1093:9: 1096:11 = note: inside `bevy_ecs::entity::Entities::entity_does_not_exist_error_details` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/entity/mod.rs:1163:23: 1163:70 = note: inside `bevy_ecs::entity::EntityDoesNotExistError::new` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/entity/mod.rs:1182:22: 1182:74 = note: inside `bevy_ecs::world::unsafe_world_cell::UnsafeWorldCell::<'_>::get_entity` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/world/unsafe_world_cell.rs:368:20: 368:73 = note: inside `<bevy_ecs::entity::Entity as bevy_ecs::world::WorldEntityFetch>::fetch_ref` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/world/entity_fetch.rs:207:21: 207:42 = note: inside `bevy_ecs::world::World::get_entity::<bevy_ecs::entity::Entity>` at /home/vj/workspace/rust/bevy/crates/bevy_ecs/src/world/mod.rs:911:18: 911:42 note: inside `main` --> src/main.rs:12:15 | 12 | world.entity(id); | ``` </details> ## Solution - remove the existing `MaybeUninit` in `EntityMeta.spawned_or_despawned` - initialize during flush. This is not needed for soundness, but not doing this means we can't return a sensible location/tick for flushed entities. ## Testing Test via the snippet above (also added equivalent test). --------- Co-authored-by: urben1680 <55257931+urben1680@users.noreply.github.com> |
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