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Update B0003 error docs to stageless (#8736)
# Objective - Fixes https://github.com/bevyengine/bevy/issues/8641 ## Solution - Update the B0003 docs to reflect the changes brought to Bevy with the release of ECS Schedule v3
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1 changed files with 36 additions and 20 deletions
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@ -43,10 +43,10 @@ fn use_entity(mut commands: Commands, entity: Option<Res<MyEntity>>) {
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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.
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The default panic message is telling you the entity id (`0v0`) and the command that failed (adding a component `Hello`):
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The default panic message is telling you the entity id (`1v0`) and the command that failed (adding a component `Hello`):
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```text
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thread 'main' panicked at 'error[B0003]: Could not add a component (of type `use_entity_after_despawn::Hello`) to entity 0v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:752:13
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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
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```
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But you don't know which system tried to add a component, and which system despawned the entity.
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@ -54,17 +54,27 @@ But you don't know which system tried to add a component, and which system despa
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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:
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```text
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0: bevy_ecs::schedule::stage::system_commands
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0: bevy_ecs::system::commands::system_commands
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with name="use_entity_after_despawn::use_entity"
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at crates/bevy_ecs/src/schedule/stage.rs:880
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1: bevy_ecs::schedule::stage
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at crates/bevy_ecs/src/system/commands/mod.rs:117
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1: bevy_ecs::world::schedule
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with name=Update
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at crates/bevy_ecs/src/schedule/mod.rs:337
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2: bevy_app::app::frame
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at crates/bevy_app/src/app.rs:113
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3: bevy_app::app::bevy_app
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at crates/bevy_app/src/app.rs:126
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thread 'main' panicked at 'error[B0003]: Could not add a component (of type `use_entity_after_despawn::Hello`) to entity 0v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:752:13
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at crates/bevy_ecs/src/world/mod.rs:1755
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2: bevy_ecs::schedule::executor::single_threaded::system
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with name="bevy_app::main_schedule::Main::run_main"
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at crates/bevy_ecs/src/schedule/executor/single_threaded.rs:98
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3: bevy_ecs::world::schedule
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with name=Main
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at crates/bevy_ecs/src/world/mod.rs:1755
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4: bevy_app::app::main app
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at crates/bevy_app/src/app.rs:249
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5: bevy_app::app::update
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at crates/bevy_app/src/app.rs:246
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6: bevy_winit::winit event_handler
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at crates/bevy_winit/src/lib.rs:338
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7: bevy_app::app::bevy_app
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at crates/bevy_app/src/app.rs:290
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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
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```
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From the first two lines, you now know that it panics while executing a command from the system `use_entity`.
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@ -72,21 +82,27 @@ From the first two lines, you now know that it panics while executing a command
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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:
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```text
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DEBUG stage{name=Update}:system_commands{name="use_entity_after_despawn::despawning"}: bevy_ecs::world: Despawning entity 0v0
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thread 'main' panicked at 'error[B0003]: Could not add a component (of type `use_entity_after_despawn::Hello`) to entity 0v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:752:13
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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
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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
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```
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From the first line, you know the entity `0v0` 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.
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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.
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Combining those two, you should get enough information to understand why this panic is happening and how to fix it:
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```text
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DEBUG stage{name=Update}:system_commands{name="use_entity_after_despawn::despawning"}: bevy_ecs::world: Despawning entity 0v0
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0: bevy_ecs::schedule::stage::system_commands
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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
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0: bevy_ecs::system::commands::system_commands
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with name="use_entity_after_despawn::use_entity"
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at crates/bevy_ecs/src/schedule/stage.rs:880
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1: bevy_ecs::schedule::stage
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at crates/bevy_ecs/src/system/commands/mod.rs:117
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1: bevy_ecs::world::schedule
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with name=Update
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at crates/bevy_ecs/src/schedule/mod.rs:337
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thread 'main' panicked at 'error[B0003]: Could not add a component (of type `use_entity_after_despawn::Hello`) to entity 0v0 because it doesn't exist in this World.', /bevy/crates/bevy_ecs/src/system/commands/mod.rs:752:13
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at crates/bevy_ecs/src/world/mod.rs:1755
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2: bevy_ecs::schedule::executor::single_threaded::system
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with name="bevy_app::main_schedule::Main::run_main"
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at crates/bevy_ecs/src/schedule/executor/single_threaded.rs:98
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3: bevy_ecs::world::schedule
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with name=Main
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at crates/bevy_ecs/src/world/mod.rs:1755
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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
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```
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