This page documents Bevy's error codes for the current release. In case you are looking for the latest error codes from Bevy's main branch, you can find them in the repository.
B0001#
To keep Rust rules on references (either one mutable reference or any number of immutable references) on a component, it is not possible to have two queries on the same component when one request mutable access to it in the same system.
Erroneous code example:
use *;
;
;
This will panic, as it's not possible to have both a mutable and an immutable query on Transform
at the same time.
You have two solutions:
Solution #1: use disjoint queries using Without
As a Player
entity won't be an Enemy
at the same time, those two queries will actually never target the same entity. This can be encoded in the query filter with Without
:
use *;
;
;
Solution #2: use a ParamSet
A ParamSet
will let you have conflicting queries as a parameter, but you will still be responsible of not using them at the same time in your system.
use *;
;
;
B0002#
To keep Rust rules on references (either one mutable reference or any number of immutable references) on a resource, it is not possible to have more than one resource of a kind if one is mutable in the same system. This can happen between Res<T>
and ResMut<T>
for the same T
, or between NonSend<T>
and NonSendMut<T>
for the same T
.
Erroneous code example:
use *;
This will panic, as it's not possible to have both a mutable and an immutable resource on State
at the same time.
As a mutable resource already provide access to the current resource value, you can remove the immutable resource.
use *;
B0003#
As commands are executed asynchronously, it is possible to issue a command on an entity that will no longer exist at the time of the command execution.
Erroneous code example:
use *;
;
;
This will panic, as system use_entity
is executed after system despawning
. Without the system ordering specified here, the ordering would be random and this code would panic half the time.
The default panic message is telling you the entity id (1v0
) and the command that failed (adding a component Hello
):
thread 'main' panicked at 'error[B0003]: Could not insert a bundle (of type `use_entity_after_despawn::Hello`) for entity 1v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:934:13
But you don't know which system tried to add a component, and which system despawned the entity.
To get the system that created the command that panics, you can enable the trace
feature of Bevy. This will add a panic handler that will print more information:
0: bevy_ecs::system::commands::system_commands
with name="use_entity_after_despawn::use_entity"
at crates/bevy_ecs/src/system/commands/mod.rs:117
1: bevy_ecs::world::schedule
with name=Update
at crates/bevy_ecs/src/world/mod.rs:1755
2: bevy_ecs::schedule::executor::single_threaded::system
with name="bevy_app::main_schedule::Main::run_main"
at crates/bevy_ecs/src/schedule/executor/single_threaded.rs:98
3: bevy_ecs::world::schedule
with name=Main
at crates/bevy_ecs/src/world/mod.rs:1755
4: bevy_app::app::main app
at crates/bevy_app/src/app.rs:249
5: bevy_app::app::update
at crates/bevy_app/src/app.rs:246
6: bevy_winit::winit event_handler
at crates/bevy_winit/src/lib.rs:338
7: bevy_app::app::bevy_app
at crates/bevy_app/src/app.rs:290
thread 'main' panicked at 'error[B0003]: Could not insert a bundle (of type `use_entity_after_despawn::Hello`) for entity 1v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:934:13
From the first two lines, you now know that it panics while executing a command from the system use_entity
.
To get the system that created the despawn command, you can enable DEBUG logs for crate bevy_ecs
, for example by setting the environment variable RUST_LOG=bevy_ecs=debug
. This will log:
DEBUG schedule{name=Main}:system{name="bevy_app::main_schedule::Main::run_main"}:schedule{name=Update}:system_commands{name="use_entity_after_despawn::despawning"}: bevy_ecs::world::entity_ref: Despawning entity 1v0
thread 'main' panicked at 'error[B0003]: Could not insert a bundle (of type `use_entity_after_despawn::Hello`) for entity 1v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:934:13
From the first line, you know the entity 1v0
was despawned when executing a command from system despawning
. In a real case, you could have many log lines, you will need to search for the exact entity from the panic message.
Combining those two, you should get enough information to understand why this panic is happening and how to fix it:
DEBUG schedule{name=Main}:system{name="bevy_app::main_schedule::Main::run_main"}:schedule{name=Update}:system_commands{name="use_entity_after_despawn::despawning"}: bevy_ecs::world::entity_ref: Despawning entity 1v0
0: bevy_ecs::system::commands::system_commands
with name="use_entity_after_despawn::use_entity"
at crates/bevy_ecs/src/system/commands/mod.rs:117
1: bevy_ecs::world::schedule
with name=Update
at crates/bevy_ecs/src/world/mod.rs:1755
2: bevy_ecs::schedule::executor::single_threaded::system
with name="bevy_app::main_schedule::Main::run_main"
at crates/bevy_ecs/src/schedule/executor/single_threaded.rs:98
3: bevy_ecs::world::schedule
with name=Main
at crates/bevy_ecs/src/world/mod.rs:1755
thread 'main' panicked at 'error[B0003]: Could not insert a bundle (of type `use_entity_after_despawn::Hello`) for entity 1v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:934:13
B0004#
A runtime warning.
An Entity
with a hierarchy-inherited component has a Parent
without the hierarchy-inherited component in question.
The hierarchy-inherited components defined in bevy include:
Third party plugins may also define their own hierarchy components, so read the warning message carefully and pay attention to the exact type of the missing component.
To fix this warning, add the missing hierarchy component to all ancestors of entities with the hierarchy component you wish to use.
The following code will cause a warning to be emitted:
use *;
// WARNING: this code is buggy
This code will not show a cube on screen.
This is because the entity spawned with commands.spawn(…)
doesn't have a ViewVisibility
or InheritedVisibility
component.
Since the cube is spawned as a child of an entity without the
visibility components, it will not be visible at all.
To fix this, you must use SpatialBundle
over TransformBundle
,
as follows:
use *;
A similar problem occurs when the GlobalTransform
component is missing.
However, when a parent GlobalTransform
is missing,
it will simply prevent all transform propagation,
including when updating the Transform
component of the child.
You will most likely encounter this warning when loading a scene
as a child of a pre-existing Entity
that does not have the proper components.
B0005#
A runtime warning.
Separate font atlases are created for each font and font size. This is expensive, and the memory is never reclaimed when e.g. interpolating TextStyle::font_size
or UiScale::scale
.
If you need to smoothly scale font size, use Transform::scale
.
You can disable this warning by setting TextSettings::allow_dynamic_font_size
to true
or raise the limit by setting TextSettings::soft_max_font_atlases
.