Commit Graph

243 Commits

Author SHA1 Message Date
Testare
da83232fa8
Let Component::map_entities defer to MapEntities (#19414)
# Objective

The objective of this PR is to enable Components to use their
`MapEntities` implementation for `Component::map_entities`.

With the improvements to the entity mapping system, there is definitely
a huge reduction in boilerplate. However, especially since
`(Entity)HashMap<..>` doesn't implement `MapEntities` (I presume because
the lack of specialization in rust makes `HashMap<Entity|X, Entity|X>`
complicated), when somebody has types that contain these hashmaps they
can't use this approach.

More so, we can't even depend on the previous implementation, since
`Component::map_entities` is used instead of
`MapEntities::map_entities`. Outside of implementing `Component `and
`Component::map_entities` on these types directly, the only path forward
is to create a custom type to wrap the hashmaps and implement map
entities on that, or split these components into a wrapper type that
implement `Component`, and an inner type that implements `MapEntities`.

## Current Solution
The solution was to allow adding `#[component(map_entities)]` on the
component. By default this will defer to the `MapEntities`
implementation.

```rust
#[derive(Component)]
#[component(map_entities)]
struct Inventory {
    items: HashMap<Entity, usize>
}

impl MapEntities for Inventory {
    fn map_entities<M: EntityMapper>(&mut self, entity_mapper: &mut M) {
        self.items = self.items
           .drain()
           .map(|(id, count)|(entity_mapper.get_mapped(id), count))
           .collect();
    }
}

```

You can use `#[component(map_entities = <function path>)]` instead to
substitute other code in for components. This function can also include
generics, but sso far I haven't been able to find a case where they are
needed.

```rust
#[derive(Component)]
#[component(map_entities = map_the_map)]
// Also works #[component(map_entities = map_the_map::<T,_>)]
struct Inventory<T> {
    items: HashMap<Entity, T>
}

fn map_the_map<T, M: EntityMapper>(inv: &mut Inventory<T>, entity_mapper: &mut M) {
    inv.items = inv.items
       .drain()
       .map(|(id, count)|(entity_mapper.get_mapped(id), count))
       .collect();
}

```

The idea is that with the previous changes to MapEntities, MapEntities
is implemented more for entity collections than for Components. If you
have a component that makes sense as both, `#[component(map_entities)]`
would work great, while otherwise a component can use
`#[component(map_entities = <function>)]` to change the behavior of
`Component::map_entities` without opening up the component type to be
included in other components.


## (Original Solution if you want to follow the PR)

The solution was to allow adding `#[component(entities)]` on the
component itself to defer to the `MapEntities` implementation

```rust
#[derive(Component)]
#[component(entities)]
struct Inventory {
    items: HashMap<Entity, usize>
}

impl MapEntities for Inventory {
    fn map_entities<M: EntityMapper>(&mut self, entity_mapper: &mut M) {
        self.items = self.items
           .drain()
           .map(|(id, count)|(entity_mapper.get_mapped(id), count))
           .collect();
    }
}

```

## Testing

I tested this by patching my local changes into my own bevy project. I
had a system that loads a scene file and executes some logic with a
Component that contains a `HashMap<Entity, UVec2>`, and it panics when
Entity is not found from another query. Since the 0.16 update this
system has reliably panicked upon attempting to the load the scene.

After patching my code in, I added `#[component(entities)]` to this
component, and I was able to successfully load the scene.

Additionally, I wrote a doc test.

## Call-outs
### Relationships
This overrules the default mapping of relationship fields. Anything else
seemed more problematic, as you'd have inconsistent behavior between
`MapEntities` and `Component`.
2025-06-23 21:05:04 +00:00
github-actions[bot]
a466084167
Bump Version after Release (#19774)
Bump version after release
This PR has been auto-generated

Fixes #19766

---------

Co-authored-by: Bevy Auto Releaser <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: François Mockers <francois.mockers@vleue.com>
Co-authored-by: François Mockers <mockersf@gmail.com>
2025-06-22 23:06:43 +00:00
urben1680
c6ae964709
EntityWorldMut methods do not automatically overwrite Relationship components (#19601)
# Objective

Some methods and commands carelessly overwrite `Relationship`
components. This may overwrite additional data stored at them which is
undesired.

Part of #19589

## Solution

A new private method will be used instead of insert:
`modify_or_insert_relation_with_relationship_hook_mode`.

This method behaves different to `insert` if `Relationship` is a larger
type than `Entity` and already contains this component. It will then use
the `modify_component` API and a new `Relationship::set_risky` method to
set the related entity, keeping all other data untouched.

For the `replace_related`(`_with_difference`) methods this also required
a `InsertHookMode` parameter for efficient modifications of multiple
children. The changes here are limited to the non-public methods.

I would appreciate feedback if this is all good.

# Testing

Added tests of all methods that previously could reset `Relationship`
data.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-06-22 00:22:05 +00:00
Giacomo Stevanato
35166d9029
Refactor bundle derive (#19749)
# Objective

- Splitted off from  #19491
- Make adding generated code to the `Bundle` derive macro easier
- Fix a bug when multiple fields are `#[bundle(ignore)]`

## Solution

- Instead of accumulating the code for each method in a different `Vec`,
accumulate only the names of non-ignored fields and their types, then
use `quote` to generate the code for each of them in the method body.
- To fix the bug, change the code populating the `BundleFieldKind` to
push only one of them per-field (previously each `#[bundle(ignore)]`
resulted in pushing twice, once for the correct
`BundleFieldKind::Ignore` and then again unconditionally for
`BundleFieldKind::Component`)

## Testing

- Added a regression test for the bug that was fixed
2025-06-20 16:36:08 +00:00
Emerson Coskey
8e1d0051d2
Fix QueryData derive codegen (#19750)
Custom derived `QueryData` impls currently generate `Item` structs with
the lifetimes swapped, which blows up the borrow checker sometimes.

See:
https://discord.com/channels/691052431525675048/749335865876021248/1385509416086011914

could add a regression test, TBH I don't know the error well enough to
do that minimally. Seems like it's that both lifetimes on
`QueryData::Item` need to be covariant, but I'm not sure.
2025-06-20 15:48:16 +00:00
Chris Russell
d0550f58ae
Remove 's lifetime from WorldQuery::Fetch (#19720)
# Objective

Unblock #18162.

#15396 added the `'s` lifetime to `QueryData::Item` to make it possible
for query items to borrow from the state. The state isn't passed
directly to `QueryData::fetch()`, so it also added the `'s` lifetime to
`WorldQuery::Fetch` so that we can pass the borrows through there.

Unfortunately, having `WorldQuery::Fetch` borrow from the state makes it
impossible to have owned state, because we store the state and the
`Fetch` in the same `struct` during iteration.

## Solution

Undo the change to add the `'s` lifetime to `WorldQuery::Fetch`.

Instead, add a `&'s Self::State` parameter to `QueryData::fetch()` and
`QueryFilter::filter_fetch()` so that borrows from the state can be
passed directly to query items.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Emerson Coskey <emerson@coskey.dev>
2025-06-19 00:58:21 +00:00
Chris Russell
f7e112a3c9
Let query items borrow from query state to avoid needing to clone (#15396)
# Objective

Improve the performance of `FilteredEntity(Ref|Mut)` and
`Entity(Ref|Mut)Except`.

`FilteredEntityRef` needs an `Access<ComponentId>` to determine what
components it can access. There is one stored in the query state, but
query items cannot borrow from the state, so it has to `clone()` the
access for each row. Cloning the access involves memory allocations and
can be expensive.


## Solution

Let query items borrow from their query state.  

Add an `'s` lifetime to `WorldQuery::Item` and `WorldQuery::Fetch`,
similar to the one in `SystemParam`, and provide `&'s Self::State` to
the fetch so that it can borrow from the state.

Unfortunately, there are a few cases where we currently return query
items from temporary query states: the sorted iteration methods create a
temporary state to query the sort keys, and the
`EntityRef::components<Q>()` methods create a temporary state for their
query.

To allow these to continue to work with most `QueryData`
implementations, introduce a new subtrait `ReleaseStateQueryData` that
converts a `QueryItem<'w, 's>` to `QueryItem<'w, 'static>`, and is
implemented for everything except `FilteredEntity(Ref|Mut)` and
`Entity(Ref|Mut)Except`.

`#[derive(QueryData)]` will generate `ReleaseStateQueryData`
implementations that apply when all of the subqueries implement
`ReleaseStateQueryData`.

This PR does not actually change the implementation of
`FilteredEntity(Ref|Mut)` or `Entity(Ref|Mut)Except`! That will be done
as a follow-up PR so that the changes are easier to review. I have
pushed the changes as chescock/bevy#5.

## Testing

I ran performance traces of many_foxes, both against main and against
chescock/bevy#5, both including #15282. These changes do appear to make
generalized animation a bit faster:

(Red is main, yellow is chescock/bevy#5)

![image](https://github.com/user-attachments/assets/de900117-0c6a-431d-ab62-c013834f97a9)


## Migration Guide

The `WorldQuery::Item` and `WorldQuery::Fetch` associated types and the
`QueryItem` and `ROQueryItem` type aliases now have an additional
lifetime parameter corresponding to the `'s` lifetime in `Query`. Manual
implementations of `WorldQuery` will need to update the method
signatures to include the new lifetimes. Other uses of the types will
need to be updated to include a lifetime parameter, although it can
usually be passed as `'_`. In particular, `ROQueryItem` is used when
implementing `RenderCommand`.

Before: 

```rust
fn render<'w>(
    item: &P,
    view: ROQueryItem<'w, Self::ViewQuery>,
    entity: Option<ROQueryItem<'w, Self::ItemQuery>>,
    param: SystemParamItem<'w, '_, Self::Param>,
    pass: &mut TrackedRenderPass<'w>,
) -> RenderCommandResult;
```

After: 

```rust
fn render<'w>(
    item: &P,
    view: ROQueryItem<'w, '_, Self::ViewQuery>,
    entity: Option<ROQueryItem<'w, '_, Self::ItemQuery>>,
    param: SystemParamItem<'w, '_, Self::Param>,
    pass: &mut TrackedRenderPass<'w>,
) -> RenderCommandResult;
```

---

Methods on `QueryState` that take `&mut self` may now result in
conflicting borrows if the query items capture the lifetime of the
mutable reference. This affects `get()`, `iter()`, and others. To fix
the errors, first call `QueryState::update_archetypes()`, and then
replace a call `state.foo(world, param)` with
`state.query_manual(world).foo_inner(param)`. Alternately, you may be
able to restructure the code to call `state.query(world)` once and then
make multiple calls using the `Query`.

Before:
```rust
let mut state: QueryState<_, _> = ...;
let d1 = state.get(world, e1);
let d2 = state.get(world, e2); // Error: cannot borrow `state` as mutable more than once at a time
println!("{d1:?}");
println!("{d2:?}");
```

After: 
```rust
let mut state: QueryState<_, _> = ...;

state.update_archetypes(world);
let d1 = state.get_manual(world, e1);
let d2 = state.get_manual(world, e2);
// OR
state.update_archetypes(world);
let d1 = state.query(world).get_inner(e1);
let d2 = state.query(world).get_inner(e2);
// OR
let query = state.query(world);
let d1 = query.get_inner(e1);
let d1 = query.get_inner(e2);

println!("{d1:?}");
println!("{d2:?}");
```
2025-06-16 21:05:41 +00:00
Joona Aalto
38c3423693
Event Split: Event, EntityEvent, and BufferedEvent (#19647)
# Objective

Closes #19564.

The current `Event` trait looks like this:

```rust
pub trait Event: Send + Sync + 'static {
    type Traversal: Traversal<Self>;
    const AUTO_PROPAGATE: bool = false;
    
    fn register_component_id(world: &mut World) -> ComponentId { ... }
    fn component_id(world: &World) -> Option<ComponentId> { ... }
}
```

The `Event` trait is used by both buffered events
(`EventReader`/`EventWriter`) and observer events. If they are observer
events, they can optionally be targeted at specific `Entity`s or
`ComponentId`s, and can even be propagated to other entities.

However, there has long been a desire to split the trait semantically
for a variety of reasons, see #14843, #14272, and #16031 for discussion.
Some reasons include:

- It's very uncommon to use a single event type as both a buffered event
and targeted observer event. They are used differently and tend to have
distinct semantics.
- A common footgun is using buffered events with observers or event
readers with observer events, as there is no type-level error that
prevents this kind of misuse.
- #19440 made `Trigger::target` return an `Option<Entity>`. This
*seriously* hurts ergonomics for the general case of entity observers,
as you need to `.unwrap()` each time. If we could statically determine
whether the event is expected to have an entity target, this would be
unnecessary.

There's really two main ways that we can categorize events: push vs.
pull (i.e. "observer event" vs. "buffered event") and global vs.
targeted:

|              | Push            | Pull                        |
| ------------ | --------------- | --------------------------- |
| **Global**   | Global observer | `EventReader`/`EventWriter` |
| **Targeted** | Entity observer | -                           |

There are many ways to approach this, each with their tradeoffs.
Ultimately, we kind of want to split events both ways:

- A type-level distinction between observer events and buffered events,
to prevent people from using the wrong kind of event in APIs
- A statically designated entity target for observer events to avoid
accidentally using untargeted events for targeted APIs

This PR achieves these goals by splitting event traits into `Event`,
`EntityEvent`, and `BufferedEvent`, with `Event` being the shared trait
implemented by all events.

## `Event`, `EntityEvent`, and `BufferedEvent`

`Event` is now a very simple trait shared by all events.

```rust
pub trait Event: Send + Sync + 'static {
    // Required for observer APIs
    fn register_component_id(world: &mut World) -> ComponentId { ... }
    fn component_id(world: &World) -> Option<ComponentId> { ... }
}
```

You can call `trigger` for *any* event, and use a global observer for
listening to the event.

```rust
#[derive(Event)]
struct Speak {
    message: String,
}

// ...

app.add_observer(|trigger: On<Speak>| {
    println!("{}", trigger.message);
});

// ...

commands.trigger(Speak {
    message: "Y'all like these reworked events?".to_string(),
});
```

To allow an event to be targeted at entities and even propagated
further, you can additionally implement the `EntityEvent` trait:

```rust
pub trait EntityEvent: Event {
    type Traversal: Traversal<Self>;
    const AUTO_PROPAGATE: bool = false;
}
```

This lets you call `trigger_targets`, and to use targeted observer APIs
like `EntityCommands::observe`:

```rust
#[derive(Event, EntityEvent)]
#[entity_event(traversal = &'static ChildOf, auto_propagate)]
struct Damage {
    amount: f32,
}

// ...

let enemy = commands.spawn((Enemy, Health(100.0))).id();

// Spawn some armor as a child of the enemy entity.
// When the armor takes damage, it will bubble the event up to the enemy.
let armor_piece = commands
    .spawn((ArmorPiece, Health(25.0), ChildOf(enemy)))
    .observe(|trigger: On<Damage>, mut query: Query<&mut Health>| {
        // Note: `On::target` only exists because this is an `EntityEvent`.
        let mut health = query.get(trigger.target()).unwrap();
        health.0 -= trigger.amount();
    });

commands.trigger_targets(Damage { amount: 10.0 }, armor_piece);
```

> [!NOTE]
> You *can* still also trigger an `EntityEvent` without targets using
`trigger`. We probably *could* make this an either-or thing, but I'm not
sure that's actually desirable.

To allow an event to be used with the buffered API, you can implement
`BufferedEvent`:

```rust
pub trait BufferedEvent: Event {}
```

The event can then be used with `EventReader`/`EventWriter`:

```rust
#[derive(Event, BufferedEvent)]
struct Message(String);

fn write_hello(mut writer: EventWriter<Message>) {
    writer.write(Message("I hope these examples are alright".to_string()));
}

fn read_messages(mut reader: EventReader<Message>) {
    // Process all buffered events of type `Message`.
    for Message(message) in reader.read() {
        println!("{message}");
    }
}
```

In summary:

- Need a basic event you can trigger and observe? Derive `Event`!
- Need the event to be targeted at an entity? Derive `EntityEvent`!
- Need the event to be buffered and support the
`EventReader`/`EventWriter` API? Derive `BufferedEvent`!

## Alternatives

I'll now cover some of the alternative approaches I have considered and
briefly explored. I made this section collapsible since it ended up
being quite long :P

<details>

<summary>Expand this to see alternatives</summary>

### 1. Unified `Event` Trait

One option is not to have *three* separate traits (`Event`,
`EntityEvent`, `BufferedEvent`), and to instead just use associated
constants on `Event` to determine whether an event supports targeting
and buffering or not:

```rust
pub trait Event: Send + Sync + 'static {
    type Traversal: Traversal<Self>;
    const AUTO_PROPAGATE: bool = false;
    const TARGETED: bool = false;
    const BUFFERED: bool = false;
    
    fn register_component_id(world: &mut World) -> ComponentId { ... }
    fn component_id(world: &World) -> Option<ComponentId> { ... }
}
```

Methods can then use bounds like `where E: Event<TARGETED = true>` or
`where E: Event<BUFFERED = true>` to limit APIs to specific kinds of
events.

This would keep everything under one `Event` trait, but I don't think
it's necessarily a good idea. It makes APIs harder to read, and docs
can't easily refer to specific types of events. You can also create
weird invariants: what if you specify `TARGETED = false`, but have
`Traversal` and/or `AUTO_PROPAGATE` enabled?

### 2. `Event` and `Trigger`

Another option is to only split the traits between buffered events and
observer events, since that is the main thing people have been asking
for, and they have the largest API difference.

If we did this, I think we would need to make the terms *clearly*
separate. We can't really use `Event` and `BufferedEvent` as the names,
since it would be strange that `BufferedEvent` doesn't implement
`Event`. Something like `ObserverEvent` and `BufferedEvent` could work,
but it'd be more verbose.

For this approach, I would instead keep `Event` for the current
`EventReader`/`EventWriter` API, and call the observer event a
`Trigger`, since the "trigger" terminology is already used in the
observer context within Bevy (both as a noun and a verb). This is also
what a long [bikeshed on
Discord](https://discord.com/channels/691052431525675048/749335865876021248/1298057661878898791)
seemed to land on at the end of last year.

```rust
// For `EventReader`/`EventWriter`
pub trait Event: Send + Sync + 'static {}

// For observers
pub trait Trigger: Send + Sync + 'static {
    type Traversal: Traversal<Self>;
    const AUTO_PROPAGATE: bool = false;
    const TARGETED: bool = false;
    
    fn register_component_id(world: &mut World) -> ComponentId { ... }
    fn component_id(world: &World) -> Option<ComponentId> { ... }
}
```

The problem is that "event" is just a really good term for something
that "happens". Observers are rapidly becoming the more prominent API,
so it'd be weird to give them the `Trigger` name and leave the good
`Event` name for the less common API.

So, even though a split like this seems neat on the surface, I think it
ultimately wouldn't really work. We want to keep the `Event` name for
observer events, and there is no good alternative for the buffered
variant. (`Message` was suggested, but saying stuff like "sends a
collision message" is weird.)

### 3. `GlobalEvent` + `TargetedEvent`

What if instead of focusing on the buffered vs. observed split, we
*only* make a distinction between global and targeted events?

```rust
// A shared event trait to allow global observers to work
pub trait Event: Send + Sync + 'static {
    fn register_component_id(world: &mut World) -> ComponentId { ... }
    fn component_id(world: &World) -> Option<ComponentId> { ... }
}

// For buffered events and non-targeted observer events
pub trait GlobalEvent: Event {}

// For targeted observer events
pub trait TargetedEvent: Event {
    type Traversal: Traversal<Self>;
    const AUTO_PROPAGATE: bool = false;
}
```

This is actually the first approach I implemented, and it has the neat
characteristic that you can only use non-targeted APIs like `trigger`
with a `GlobalEvent` and targeted APIs like `trigger_targets` with a
`TargetedEvent`. You have full control over whether the entity should or
should not have a target, as they are fully distinct at the type-level.

However, there's a few problems:

- There is no type-level indication of whether a `GlobalEvent` supports
buffered events or just non-targeted observer events
- An `Event` on its own does literally nothing, it's just a shared trait
required to make global observers accept both non-targeted and targeted
events
- If an event is both a `GlobalEvent` and `TargetedEvent`, global
observers again have ambiguity on whether an event has a target or not,
undermining some of the benefits
- The names are not ideal

### 4. `Event` and `EntityEvent`

We can fix some of the problems of Alternative 3 by accepting that
targeted events can also be used in non-targeted contexts, and simply
having the `Event` and `EntityEvent` traits:

```rust
// For buffered events and non-targeted observer events
pub trait Event: Send + Sync + 'static {
    fn register_component_id(world: &mut World) -> ComponentId { ... }
    fn component_id(world: &World) -> Option<ComponentId> { ... }
}

// For targeted observer events
pub trait EntityEvent: Event {
    type Traversal: Traversal<Self>;
    const AUTO_PROPAGATE: bool = false;
}
```

This is essentially identical to this PR, just without a dedicated
`BufferedEvent`. The remaining major "problem" is that there is still
zero type-level indication of whether an `Event` event *actually*
supports the buffered API. This leads us to the solution proposed in
this PR, using `Event`, `EntityEvent`, and `BufferedEvent`.

</details>

## Conclusion

The `Event` + `EntityEvent` + `BufferedEvent` split proposed in this PR
aims to solve all the common problems with Bevy's current event model
while keeping the "weirdness" factor minimal. It splits in terms of both
the push vs. pull *and* global vs. targeted aspects, while maintaining a
shared concept for an "event".

### Why I Like This

- The term "event" remains as a single concept for all the different
kinds of events in Bevy.
- Despite all event types being "events", they use fundamentally
different APIs. Instead of assuming that you can use an event type with
any pattern (when only one is typically supported), you explicitly opt
in to each one with dedicated traits.
- Using separate traits for each type of event helps with documentation
and clearer function signatures.
- I can safely make assumptions on expected usage.
- If I see that an event is an `EntityEvent`, I can assume that I can
use `observe` on it and get targeted events.
- If I see that an event is a `BufferedEvent`, I can assume that I can
use `EventReader` to read events.
- If I see both `EntityEvent` and `BufferedEvent`, I can assume that
both APIs are supported.

In summary: This allows for a unified concept for events, while limiting
the different ways to use them with opt-in traits. No more guess-work
involved when using APIs.

### Problems?

- Because `BufferedEvent` implements `Event` (for more consistent
semantics etc.), you can still use all buffered events for non-targeted
observers. I think this is fine/good. The important part is that if you
see that an event implements `BufferedEvent`, you know that the
`EventReader`/`EventWriter` API should be supported. Whether it *also*
supports other APIs is secondary.
- I currently only support `trigger_targets` for an `EntityEvent`.
However, you can technically target components too, without targeting
any entities. I consider that such a niche and advanced use case that
it's not a huge problem to only support it for `EntityEvent`s, but we
could also split `trigger_targets` into `trigger_entities` and
`trigger_components` if we wanted to (or implement components as
entities :P).
- You can still trigger an `EntityEvent` *without* targets. I consider
this correct, since `Event` implements the non-targeted behavior, and
it'd be weird if implementing another trait *removed* behavior. However,
it does mean that global observers for entity events can technically
return `Entity::PLACEHOLDER` again (since I got rid of the
`Option<Entity>` added in #19440 for ergonomics). I think that's enough
of an edge case that it's not a huge problem, but it is worth keeping in
mind.
- ~~Deriving both `EntityEvent` and `BufferedEvent` for the same type
currently duplicates the `Event` implementation, so you instead need to
manually implement one of them.~~ Changed to always requiring `Event` to
be derived.

## Related Work

There are plans to implement multi-event support for observers,
especially for UI contexts. [Cart's
example](https://github.com/bevyengine/bevy/issues/14649#issuecomment-2960402508)
API looked like this:

```rust
// Truncated for brevity
trigger: Trigger<(
    OnAdd<Pressed>,
    OnRemove<Pressed>,
    OnAdd<InteractionDisabled>,
    OnRemove<InteractionDisabled>,
    OnInsert<Hovered>,
)>,
```

I believe this shouldn't be in conflict with this PR. If anything, this
PR might *help* achieve the multi-event pattern for entity observers
with fewer footguns: by statically enforcing that all of these events
are `EntityEvent`s in the context of `EntityCommands::observe`, we can
avoid misuse or weird cases where *some* events inside the trigger are
targeted while others are not.
2025-06-15 16:46:34 +00:00
Chris Russell
bb4ea9c28b
Stop storing access for all systems (#19477)
# Objective

Reduce memory usage by storing fewer copies of
`FilteredAccessSet<ComponentId>`.

Currently, the `System` trait exposes the `component_access_set` for the
system, which is used by the multi-threaded executor to determine which
systems can run concurrently. But because it is available on the trait,
it needs to be stored for *every* system, even ones that are not run by
the executor! In particular, it is never needed for observers, or for
the inner systems in a `PipeSystem` or `CombinatorSystem`.


## Solution

Instead of exposing the access from a method on `System`, return it from
`System::initialize`. Since it is still needed during scheduling, store
the access alongside the boxed system in the schedule.

That's not quite enough for systems built using `SystemParamBuilder`s,
though. Those calculate the access in `SystemParamBuilder::build`, which
happens earlier than `System::initialize`. To handle those, we separate
`SystemParam::init_state` into `init_state`, which creates the state
value, and `init_access`, which calculates the access. This lets
`System::initialize` call `init_access` on a state that was provided by
the builder.

An additional benefit of that separation is that it removes the need to
duplicate access checks between `SystemParamBuilder::build` and
`SystemParam::init_state`.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-06-13 17:56:09 +00:00
Alice Cecile
6ddd0f16a8
Component lifecycle reorganization and documentation (#19543)
# Objective

I set out with one simple goal: clearly document the differences between
each of the component lifecycle events via module docs.

Unfortunately, no such module existed: the various lifecycle code was
scattered to the wind.
Without a unified module, it's very hard to discover the related types,
and there's nowhere good to put my shiny new documentation.

## Solution

1. Unify the assorted types into a single
`bevy_ecs::component_lifecycle` module.
2. Write docs.
3. Write a migration guide.

## Testing

Thanks CI!

## Follow-up

1. The lifecycle event names are pretty confusing, especially
`OnReplace`. We should consider renaming those. No bikeshedding in my PR
though!
2. Observers need real module docs too :(
3. Any additional functional changes should be done elsewhere; this is a
simple docs and re-org PR.

---------

Co-authored-by: theotherphil <phil.j.ellison@gmail.com>
2025-06-10 00:59:16 +00:00
Marcel Müller
2768af5d2d
Allow not emitting BundleFromComponents with Bundle derive macro (#19249)
# Objective

Fixes #19136

## Solution

- Add a new container attribute which when set does not emit
`BundleFromComponents`

## Testing

- Did you test these changes?

Yes, a new test was added.

- Are there any parts that need more testing?

Since `BundleFromComponents` is unsafe I made extra sure that I did not
misunderstand its purpose. As far as I can tell, _not_ implementing it
is ok.

- How can other people (reviewers) test your changes? Is there anything
specific they need to know?

Nope

- If relevant, what platforms did you test these changes on, and are
there any important ones you can't test?

I don't think the platform is relevant

---



One thing I am not sure about is how to document this? I'll gladly add
it

---------

Signed-off-by: Marcel Müller <neikos@neikos.email>
2025-06-09 20:15:42 +00:00
theotherphil
6b5289bd5e
deny(missing_docs) for bevy_ecs_macros (#19523)
# Objective

Deny missing docs for bevy_ecs_macros, towards
https://github.com/bevyengine/bevy/issues/3492.

## Solution

More docs of the form

```
/// Does the thing
fn do_the_thing() {}
```

But I don't think the derive macros are where anyone is going to be
looking for details of these concepts and deny(missing_docs) inevitably
results in some items having noddy docs.
2025-06-08 16:28:31 +00:00
SpecificProtagonist
a266e7e642
More uninlined_format_args fixes (#19396)
# Objective

There are several uninlined format args (seems to be in more formatting
macros and in more crates) that are not detected on stable, but are on
nightly.

## Solution

Fix them.
2025-05-28 02:35:18 +00:00
Chris Russell
571b3ba475
Remove ArchetypeComponentId and archetype_component_access (#19143)
# Objective

Remove `ArchetypeComponentId` and `archetype_component_access`.
Following #16885, they are no longer used by the engine, so we can stop
spending time calculating them or space storing them.

## Solution

Remove `ArchetypeComponentId` and everything that touches it.  

The `System::update_archetype_component_access` method no longer needs
to update `archetype_component_access`. We do still need to update query
caches, but we no longer need to do so *before* running the system. We'd
have to touch every caller anyway if we gave the method a better name,
so just remove `System::update_archetype_component_access` and
`SystemParam::new_archetype` entirely, and update the query cache in
`Query::get_param`.

The `Single` and `Populated` params also need their query caches updated
in `SystemParam::validate_param`, so change `validate_param` to take
`&mut Self::State` instead of `&Self::State`.
2025-05-27 19:04:32 +00:00
Emerson Coskey
fb2d79ad60
Better macro errors for get_struct_fields (#17639)
# Objective

- Currently, the error span for `get_struct_field` when encountering an
enum or union points to the macro invocation, rather than the `enum` or
`union` token. It also doesn't mention which macro reported the error.

## Solution

- Report the correct error span
- Add parameter for passing in the name of the macro invocation

## Testing

Bevy compiles fine with this change

## Migration Guide

```rs
// before
let fields = get_struct_fields(&ast.data);

// after
let fields = get_struct_fields(&ast.data, "derive(Bundle)");
```

---------

Co-authored-by: Chris Russell <8494645+chescock@users.noreply.github.com>
2025-05-26 16:57:03 +00:00
Tim
4924cf5828
Remove upcasting methods + Cleanup interned label code (#18984)
Hiya!

# Objective

- Remove upcasting methods that are no longer necessary since Rust 1.86.
- Cleanup the interned label code.
 
## Notes
- I didn't try to remove the upcasting methods from `bevy_reflect`, as
there appears to be some complexity related to remote type reflection.
- There are likely some other upcasting methods floating around.

## Testing
I ran the `breakout` example to check that the hashing/eq
implementations of the labels are still correct.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-05-26 15:38:12 +00:00
mgi388
01d2b8571c
Remove dead states code from bevy_ecs (#19210)
`bevy_ecs` was meant to have the `States` and `SubStates`
`proc_macro_derive`s removed when the separate `bevy_state` [was
created](https://github.com/bevyengine/bevy/issues/13216) but they were
missed.
2025-05-14 13:19:20 +00:00
Jordan Dominion
86cc02dca2
Fix macro pollution in SystemParam derive (#19155)
# Objective

Fixes #19130 

## Solution

Fully quality `Result::Ok` so as to not accidentally invoke the anyhow
function of the same name

## Testing

Tested on this minimal repro with and without change.

main.rs
```rs
use anyhow::Ok;
use bevy::ecs::system::SystemParam;

#[derive(SystemParam)]
pub struct SomeParams;

fn main() {
}
```
Cargo.toml
```toml
[package]
name = "bevy-playground"
version = "0.1.0"
edition = "2024"

[dependencies]
anyhow = "1.0.98"
bevy = { path = "../bevy" }
```
2025-05-10 02:45:25 +00:00
Tim Overbeek
60cdefd128
Derive clone_behavior for Components (#18811)
Allow Derive(Component) to specify a clone_behavior

```rust
#[derive(Component)]
#[component(clone_behavior = Ignore)]
MyComponent;
```
2025-05-06 00:32:59 +00:00
Chris Russell
bea0a0a9bc
Let FilteredEntity(Ref|Mut) receive access when nested. (#18236)
# Objective

Let `FilteredEntityRef` and `FilteredEntityMut` receive access when
nested inside tuples or `#[derive(QueryData)]` types. Make sure to
exclude any access that would conflict with other subqueries!

Fixes #14349

## Solution

Replace `WorldQuery::set_access(state, access)` with a new method,
`QueryData::provide_extra_access(state, access, available_access)`, that
passes both the total available access and the currently used access.
This is called after `WorldQuery::update_component_access()`, so any
access used by ordinary subqueries will be known. `FilteredEntityRef`
and `FilteredEntityMut` can use the combination to determine how much
access they can safely take, while tuples can safely pass those
parameters directly to their subqueries.

This requires a new `Access::remove_conflicting_access()` method that
can be used to remove any access that would conflict with existing
access. Implementing this method was easier by first factoring some
common set manipulation code out of `Access::extend`. I can extract that
refactoring to a separate PR if desired.

Have `FilteredEntity(Ref|Mut)` store `Access` instead of
`FilteredAccess` because they do not need to keep track of the filter.
This was necessary in an early draft but no longer is. I left it in
because it's small and I'm touching that code anyway, but I can extract
it to a separate PR if desired.
2025-05-05 23:23:46 +00:00
Tim Overbeek
e02c3662fb
Code quality cleanup pass for #[require] (#18621)
#18555 improved syntax for required components.

However some code was a bit redundant after the new parsing and struct
initializing would not give proper errors.
This PR fixes that.

---------

Co-authored-by: Tim Overbeek <oorbecktim@Tims-MacBook-Pro.local>
2025-04-02 20:09:04 +00:00
Chris Russell
9e240ee99a
Improve error message for missing events (#18683)
# Objective

Improve the parameter validation error message for
`Event(Reader|Writer|Mutator)`.

System parameters defined using `#[derive(SystemParam)]`, including the
parameters for events, currently propagate the validation errors from
their subparameters. The error includes the type of the failing
parameter, so the resulting error includes the type of the failing
subparameter instead of the derived parameter.

In particular, `EventReader<T>` will report an error from a
`Res<Events<T>>`, even though the user has no parameter of that type!

This is a follow-up to #18593.

## Solution

Have `#[derive]`d system parameters map errors during propagation so
that they report the outer parameter type.

To continue to provide context, add a field to
`SystemParamValidationError` that identifies the subparameter by name,
and is empty for non-`#[derive]`d parameters.

Allow them to override the failure message for individual parameters.
Use this to convert "Resource does not exist" to "Event not initialized"
for `Event(Reader|Writer|Mutator)`.

## Showcase

The validation error for a `EventReader<SomeEvent>` parameter when
`add_event` has not been called changes from:

Before: 
```
Parameter `Res<Events<SomeEvent>>` failed validation: Resource does not exist
```

After
```
Parameter `EventReader<SomeEvent>::events` failed validation: Event not initialized
```
2025-04-02 19:25:48 +00:00
krunchington
83ffc90c6c
Fix relationship macro for multiple named members fields (#18530)
# Objective

Fixes #18466 

## Solution

Updated the macro generation pattern to place the comma in the correct
place in the pattern.

## Testing

- Tried named and unnamed fields in combination, and used rust expand
macro tooling to see the generated code and verify its correctness (see
screenshots in example below)

---

## Showcase

Screenshot showing expanded macro with multiple named fields

![image](https://github.com/user-attachments/assets/7ecd324c-10ba-4b23-9b53-b94da03567d3)

Screenshot showing expanded macro with single unnamed field

![image](https://github.com/user-attachments/assets/be72f061-5f07-4d19-b5f6-7ff6c35ec679)

## Migration Guide

n/a
2025-03-27 21:35:47 +00:00
Carter Anderson
1ba9da0812
Required Components: pass through all tokens in {} and () syntax (#18578)
# Objective

#18555 added improved require syntax, but inline structs didn't support
`..Default::default()` syntax (for technical reasons we can't parse the
struct directly, so there is manual logic that missed this case).

## Solution

When a `{}` or `()` section is encountered for a required component,
rather than trying to parse the fields directly, just pass _all_ of the
tokens through. This ensures no tokens are dropped, protects us against
any future syntax changes, and optimizes our parsing logic (as we're
dropping the field parsing logic entirely).
2025-03-27 21:20:08 +00:00
Carter Anderson
538afe2330
Improved Require Syntax (#18555)
# Objective

Requires are currently more verbose than they need to be. People would
like to define inline component values. Additionally, the current
`#[require(Foo(custom_constructor))]` and `#[require(Foo(|| Foo(10))]`
syntax doesn't really make sense within the context of the Rust type
system. #18309 was an attempt to improve ergonomics for some cases, but
it came at the cost of even more weirdness / unintuitive behavior. Our
approach as a whole needs a rethink.

## Solution

Rework the `#[require()]` syntax to make more sense. This is a breaking
change, but I think it will make the system easier to learn, while also
improving ergonomics substantially:

```rust
#[derive(Component)]
#[require(
    A, // this will use A::default()
    B(1), // inline tuple-struct value
    C { value: 1 }, // inline named-struct value
    D::Variant, // inline enum variant
    E::SOME_CONST, // inline associated const
    F::new(1), // inline constructor
    G = returns_g(), // an expression that returns G
    H = SomethingElse::new(), // expression returns SomethingElse, where SomethingElse: Into<H> 
)]
struct Foo;
```

## Migration Guide

Custom-constructor requires should use the new expression-style syntax:

```rust
// before
#[derive(Component)]
#[require(A(returns_a))]
struct Foo;

// after
#[derive(Component)]
#[require(A = returns_a())]
struct Foo;
```

Inline-closure-constructor requires should use the inline value syntax
where possible:

```rust
// before
#[derive(Component)]
#[require(A(|| A(10))]
struct Foo;

// after
#[derive(Component)]
#[require(A(10)]
struct Foo;
```

In cases where that is not possible, use the expression-style syntax:

```rust
// before
#[derive(Component)]
#[require(A(|| A(10))]
struct Foo;

// after
#[derive(Component)]
#[require(A = A(10)]
struct Foo;
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: François Mockers <mockersf@gmail.com>
2025-03-26 17:48:27 +00:00
Chris Russell
837991a5b5
Replace ValidationOutcome with Result (#18541)
# Objective

Make it easier to short-circuit system parameter validation.  

Simplify the API surface by combining `ValidationOutcome` with
`SystemParamValidationError`.

## Solution

Replace `ValidationOutcome` with `Result<(),
SystemParamValidationError>`. Move the docs from `ValidationOutcome` to
`SystemParamValidationError`.

Add a `skipped` field to `SystemParamValidationError` to distinguish the
`Skipped` and `Invalid` variants.

Use the `?` operator to short-circuit validation in tuples of system
params.
2025-03-26 03:36:16 +00:00
Alice Cecile
6a981aaa6f
Define system param validation on a per-system parameter basis (#18504)
# Objective

When introduced, `Single` was intended to simply be silently skipped,
allowing for graceful and efficient handling of systems during invalid
game states (such as when the player is dead).

However, this also caused missing resources to *also* be silently
skipped, leading to confusing and very hard to debug failures. In
0.15.1, this behavior was reverted to a panic, making missing resources
easier to debug, but largely making `Single` (and `Populated`)
worthless, as they would panic during expected game states.

Ultimately, the consensus is that this behavior should differ on a
per-system-param basis. However, there was no sensible way to *do* that
before this PR.

## Solution

Swap `SystemParam::validate_param` from a `bool` to:

```rust
/// The outcome of system / system param validation,
/// used by system executors to determine what to do with a system.
pub enum ValidationOutcome {
    /// All system parameters were validated successfully and the system can be run.
    Valid,
    /// At least one system parameter failed validation, and an error must be handled.
    /// By default, this will result in1 a panic. See [crate::error] for more information.
    ///
    /// This is the default behavior, and is suitable for system params that should *always* be valid,
    /// either because sensible fallback behavior exists (like [`Query`] or because
    /// failures in validation should be considered a bug in the user's logic that must be immediately addressed (like [`Res`]).
    Invalid,
    /// At least one system parameter failed validation, but the system should be skipped due to [`ValidationBehavior::Skip`].
    /// This is suitable for system params that are intended to only operate in certain application states, such as [`Single`].
    Skipped,
}
```
Then, inside of each `SystemParam` implementation, return either Valid,
Invalid or Skipped.

Currently, only `Single`, `Option<Single>` and `Populated` use the
`Skipped` behavior. Other params (like resources) retain their current
failing

## Testing

Messed around with the fallible_params example. Added a pair of tests:
one for panicking when resources are missing, and another for properly
skipping `Single` and `Populated` system params.

## To do

- [x] get https://github.com/bevyengine/bevy/pull/18454 merged
- [x] fix the todo!() in the macro-powered tuple implementation (please
help 🥺)
- [x] test
- [x] write a migration guide
- [x] update the example comments

## Migration Guide

Various system and system parameter validation methods
(`SystemParam::validate_param`, `System::validate_param` and
`System::validate_param_unsafe`) now return and accept a
`ValidationOutcome` enum, rather than a `bool`. The previous `true`
values map to `ValidationOutcome::Valid`, while `false` maps to
`ValidationOutcome::Invalid`.

However, if you wrote a custom schedule executor, you should now respect
the new `ValidationOutcome::Skipped` parameter, skipping any systems
whose validation was skipped. By contrast, `ValidationOutcome::Invalid`
systems should also be skipped, but you should call the
`default_error_handler` on them first, which by default will result in a
panic.

If you are implementing a custom `SystemParam`, you should consider
whether failing system param validation is an error or an expected
state, and choose between `Invalid` and `Skipped` accordingly. In Bevy
itself, `Single` and `Populated` now once again skip the system when
their conditions are not met. This is the 0.15.0 behavior, but stands in
contrast to the 0.15.1 behavior, where they would panic.

---------

Co-authored-by: MiniaczQ <xnetroidpl@gmail.com>
Co-authored-by: Dmytro Banin <banind@cs.washington.edu>
Co-authored-by: Chris Russell <8494645+chescock@users.noreply.github.com>
2025-03-25 04:27:20 +00:00
Carter Anderson
a033f1b206
Replace VisitEntities with MapEntities (#18432)
# Objective

There are currently too many disparate ways to handle entity mapping,
especially after #17687. We now have MapEntities, VisitEntities,
VisitEntitiesMut, Component::visit_entities,
Component::visit_entities_mut.

Our only known use case at the moment for these is entity mapping. This
means we have significant consolidation potential.

Additionally, VisitEntitiesMut cannot be implemented for map-style
collections like HashSets, as you cant "just" mutate a `&mut Entity`.
Our current approach to Component mapping requires VisitEntitiesMut,
meaning this category of entity collection isn't mappable. `MapEntities`
is more generally applicable. Additionally, the _existence_ of the
blanket From impl on VisitEntitiesMut blocks us from implementing
MapEntities for HashSets (or any types we don't own), because the owner
could always add a conflicting impl in the future.

## Solution

Use `MapEntities` everywhere and remove all "visit entities" usages.

* Add `Component::map_entities`
* Remove `Component::visit_entities`, `Component::visit_entities_mut`,
`VisitEntities`, and `VisitEntitiesMut`
* Support deriving `Component::map_entities` in `#[derive(Coomponent)]`
* Add `#[derive(MapEntities)]`, and share logic with the
`Component::map_entities` derive.
* Add `ComponentCloneCtx::queue_deferred`, which is command-like logic
that runs immediately after normal clones. Reframe `FromWorld` fallback
logic in the "reflect clone" impl to use it. This cuts out a lot of
unnecessary work and I think justifies the existence of a pseudo-command
interface (given how niche, yet performance sensitive this is).

Note that we no longer auto-impl entity mapping for ` IntoIterator<Item
= &'a Entity>` types, as this would block our ability to implement cases
like `HashMap`. This means the onus is on us (or type authors) to add
explicit support for types that should be mappable.

Also note that the Component-related changes do not require a migration
guide as there hasn't been a release with them yet.

## Migration Guide

If you were previously implementing `VisitEntities` or
`VisitEntitiesMut` (likely via a derive), instead use `MapEntities`.
Those were almost certainly used in the context of Bevy Scenes or
reflection via `ReflectMapEntities`. If you have a case that uses
`VisitEntities` or `VisitEntitiesMut` directly, where `MapEntities` is
not a viable replacement, please let us know!

```rust
// before
#[derive(VisitEntities, VisitEntitiesMut)]
struct Inventory {
  items: Vec<Entity>,
  #[visit_entities(ignore)]
  label: String,
}

// after
#[derive(MapEntities)]
struct Inventory {
  #[entities]
  items: Vec<Entity>,
  label: String,
}
```
2025-03-21 00:18:10 +00:00
Wuketuke
55fd10502c
Required components accept const values (#16720) (#18309)
# Objective

Const values should be more ergonomic to insert, since this is too
verbose
``` rust
#[derive(Component)]
#[require(
    LockedAxes(||LockedAxes::ROTATION_LOCKED),
)]
pub struct CharacterController;
```
instead, users can now abbreviate that nonsense like this
``` rust
#[derive(Component)]
#[require(
    LockedAxes = ROTATION_LOCKED),
)]
pub struct CharacterController;
```
it also works for enum labels.
I chose to omit the type, since were trying to reduce typing here. The
alternative would have been this:
```rust
#[require(
    LockedAxes = LockedAxes::ROTATION_LOCKED),
)]
```
This of course has its disadvantages, since the const has to be
associated, but the old closure method is still possible, so I dont
think its a problem.
- Fixes #16720

## Testing

I added one new test in the docs, which also explain the new change. I
also saw that the docs for the required components on line 165 was
missing an assertion, so I added it back in

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-03-21 00:02:10 +00:00
Eagster
246ce590e5
Queued component registration (#18173)
# Objective

This is an alternative to #17871 and #17701 for tracking issue #18155.
This thanks to @maniwani for help with this design.

The goal is to enable component ids to be reserved from multiple threads
concurrently and with only `&World`. This contributes to assets as
entities, read-only query and system parameter initialization, etc.

## What's wrong with #17871 ?

In #17871, I used my proposed staging utilities to allow *fully*
registering components from any thread concurrently with only
`&Components`. However, if we want to pursue components as entities
(which is desirable for a great many reasons. See
[here](https://discord.com/channels/691052431525675048/692572690833473578/1346499196655505534)
on discord), this staging isn't going to work. After all, if registering
a component requires spawning an entity, and spawning an entity requires
`&mut World`, it is impossible to register a component fully with only
`&World`.

## Solution

But what if we don't have to register it all the way? What if it's
enough to just know the `ComponentId` it will have once it is registered
and to queue it to be registered at a later time? Spoiler alert: That is
all we need for these features.

Here's the basic design:

Queue a registration:

1. Check if it has already been registered.
2. Check if it has already been queued.
3. Reserve a `ComponentId`.
4. Queue the registration at that id.

Direct (normal) registration:

1. Check if this registration has been queued.
2. If it has, use the queued registration instead.
3. Otherwise, proceed like normal.

Appllying the queue:

1. Pop queued items off one by one.
2. Register them directly.

One other change:

The whole point of this design over #17871 is to facilitate coupling
component registration with the World. To ensure that this would fully
work with that, I went ahead and moved the `ComponentId` generator onto
the world itself. That stemmed a couple of minor organizational changes
(see migration guide). As we do components as entities, we will replace
this generator with `Entities`, which lives on `World` too. Doing this
move early let me verify the design and will reduce migration headaches
in the future. If components as entities is as close as I think it is, I
don't think splitting this up into different PRs is worth it. If it is
not as close as it is, it might make sense to still do #17871 in the
meantime (see the risks section). I'll leave it up to y'all what we end
up doing though.

## Risks and Testing

The biggest downside of this compared to #17871 is that now we have to
deal with correct but invalid `ComponentId`s. They are invalid because
the component still isn't registered, but they are correct because, once
registered, the component will have exactly that id.

However, the only time this becomes a problem is if some code violates
safety rules by queuing a registration and using the returned id as if
it was valid. As this is a new feature though, nothing in Bevy does
this, so no new tests were added for it. When we do use it, I left
detailed docs to help mitigate issues here, and we can test those
usages. Ex: we will want some tests on using queries initialized from
queued registrations.

## Migration Guide

Component registration can now be queued with only `&World`. To
facilitate this, a few APIs needed to be moved around.

The following functions have moved from `Components` to
`ComponentsRegistrator`:

- `register_component`
- `register_component_with_descriptor`
- `register_resource_with_descriptor`
- `register_non_send`
- `register_resource`
- `register_required_components_manual`

Accordingly, functions in `Bundle` and `Component` now take
`ComponentsRegistrator` instead of `Components`.
You can obtain `ComponentsRegistrator` from the new
`World::components_registrator`.
You can obtain `ComponentsQueuedRegistrator` from the new
`World::components_queue`, and use it to stage component registration if
desired.

# Open Question

Can we verify that it is enough to queue registration with `&World`? I
don't think it would be too difficult to package this up into a
`Arc<MyComponentsManager>` type thing if we need to, but keeping this on
`&World` certainly simplifies things. If we do need the `Arc`, we'll
need to look into partitioning `Entities` for components as entities, so
we can keep most of the allocation fast on `World` and only keep a
smaller partition in the `Arc`. I'd love an SME on assets as entities to
shed some light on this.

---------

Co-authored-by: andriyDev <andriydzikh@gmail.com>
2025-03-10 21:46:27 +00:00
Tim Overbeek
664000f848
Improve derive(Event) and simplify macro code (#18083)
# Objective

simplify some code and improve Event macro

Closes https://github.com/bevyengine/bevy/issues/14336,


# Showcase

you can now write derive Events like so
```rust
#[derive(event)]
#[event(auto_propagate, traversal = MyType)]
struct MyEvent;
```
2025-03-07 02:01:23 +00:00
RobWalt
a85a3a2a15
allow Call and Closure expressions in hook macro attributes (#18017)
# Objective

This PR adds:

- function call hook attributes `#[component(on_add = func(42))]`
  - main feature of this commit
- closure hook attributes `#[component(on_add = |w, ctx| { /* ... */
})]`
  - maybe too verbose
  - but was easy to add
  - was suggested on discord

This allows to reuse common functionality without replicating a lot of
boilerplate. A small example is a hook which just adds different default
sprites. The sprite loading code would be the same for every component.
Unfortunately we can't use the required components feature, since we
need at least an `AssetServer` or other `Resource`s or `Component`s to
load the sprite.

```rs
fn load_sprite(path: &str) -> impl Fn(DeferredWorld, HookContext) {
  |mut world, ctx| {
    // ... use world to load sprite
  }
}

#[derive(Component)]
#[component(on_add = load_sprite("knight.png"))]
struct Knight;

#[derive(Component)]
#[component(on_add = load_sprite("monster.png"))]
struct Monster;
```

---

The commit also reorders the logic of the derive macro a bit. It's
probably a bit less lazy now, but the functionality shouldn't be
performance critical and is executed at compile time anyways.

## Solution

- Introduce `HookKind` enum in the component proc macro module
- extend parsing to allow more cases of expressions

## Testing

I have some code laying around. I'm not sure where to put it yet though.
Also is there a way to check compilation failures? Anyways, here it is:

```rs
use bevy::prelude::*;

#[derive(Component)]
#[component(
    on_add = fooing_and_baring,
    on_insert = fooing_and_baring,
    on_replace = fooing_and_baring,
    on_despawn = fooing_and_baring,
    on_remove = fooing_and_baring
)]
pub struct FooPath;

fn fooing_and_baring(
    world: bevy::ecs::world::DeferredWorld,
    ctx: bevy::ecs::component::HookContext,
) {
}

#[derive(Component)]
#[component(
    on_add = baring_and_bazzing("foo"),
    on_insert = baring_and_bazzing("foo"),
    on_replace = baring_and_bazzing("foo"),
    on_despawn = baring_and_bazzing("foo"),
    on_remove = baring_and_bazzing("foo")
)]
pub struct FooCall;

fn baring_and_bazzing(
    path: &str,
) -> impl Fn(bevy::ecs::world::DeferredWorld, bevy::ecs::component::HookContext) {
    |world, ctx| {}
}

#[derive(Component)]
#[component(
    on_add = |w,ctx| {},
    on_insert = |w,ctx| {},
    on_replace = |w,ctx| {},
    on_despawn = |w,ctx| {},
    on_remove = |w,ctx| {}
)]
pub struct FooClosure;

#[derive(Component, Debug)]
#[relationship(relationship_target = FooTargets)]
#[component(
    on_add = baring_and_bazzing("foo"),
    // on_insert = baring_and_bazzing("foo"),
    // on_replace = baring_and_bazzing("foo"),
    on_despawn = baring_and_bazzing("foo"),
    on_remove = baring_and_bazzing("foo")
)]
pub struct FooTargetOf(Entity);

#[derive(Component, Debug)]
#[relationship_target(relationship = FooTargetOf)]
#[component(
    on_add = |w,ctx| {},
    on_insert = |w,ctx| {},
    // on_replace = |w,ctx| {},
    // on_despawn = |w,ctx| {},
    on_remove = |w,ctx| {}
)]
pub struct FooTargets(Vec<Entity>);

// MSG:  mismatched types  expected fn pointer `for<'w> fn(bevy::bevy_ecs::world::DeferredWorld<'w>, bevy::bevy_ecs::component::HookContext)`    found struct `Bar`
//
// pub struct Bar;
// #[derive(Component)]
// #[component(
//     on_add = Bar,
// )]
// pub struct FooWrongPath;

// MSG: this function takes 1 argument but 2 arguements were supplied
//
// #[derive(Component)]
// #[component(
//     on_add = wrong_bazzing("foo"),
// )]
// pub struct FooWrongCall;
//
// fn wrong_bazzing(path: &str) -> impl Fn(bevy::ecs::world::DeferredWorld) {
//     |world| {}
// }

// MSG: expected 1 argument, found 2
//
// #[derive(Component)]
// #[component(
//     on_add = |w| {},
// )]
// pub struct FooWrongCall;
```

---

## Showcase

I'll try to continue to work on this to have a small section in the
release notes.
2025-03-06 16:39:11 +00:00
Carter Anderson
06cb5c5fd9
Fix Component require() IDE integration (#18165)
# Objective

Component `require()` IDE integration is fully broken, as of #16575.

## Solution

This reverts us back to the previous "put the docs on Component trait"
impl. This _does_ reduce the accessibility of the required components in
rust docs, but the complete erasure of "required component IDE
experience" is not worth the price of slightly increased prominence of
requires in docs.

Additionally, Rust Analyzer has recently started including derive
attributes in suggestions, so we aren't losing that benefit of the
proc_macro attribute impl.
2025-03-06 02:44:47 +00:00
Carter Anderson
a530c07bc5
Preserve spawned RelationshipTarget order and other improvements (#17858)
Fixes #17720

## Objective

Spawning RelationshipTargets from scenes currently fails to preserve
RelationshipTarget ordering (ex: `Children` has an arbitrary order).
This is because it uses the normal hook flow to set up the collection,
which means we are pushing onto the collection in _spawn order_ (which
is currently in archetype order, which will often produce mismatched
orderings).

We need to preserve the ordering in the original RelationshipTarget
collection. Ideally without expensive checking / fixups.

## Solution

One solution would be to spawn in hierarchy-order. However this gets
complicated as there can be multiple hierarchies, and it also means we
can't spawn in more cache-friendly orders (ex: the current per-archetype
spawning, or future even-smarter per-table spawning). Additionally,
same-world cloning has _slightly_ more nuanced needs (ex: recursively
clone linked relationships, while maintaining _original_ relationships
outside of the tree via normal hooks).

The preferred approach is to directly spawn the remapped
RelationshipTarget collection, as this trivially preserves the ordering.
Unfortunately we can't _just_ do that, as when we spawn the children
with their Relationships (ex: `ChildOf`), that will insert a duplicate.

We could "fixup" the collection retroactively by just removing the back
half of duplicates, but this requires another pass / more lookups /
allocating twice as much space. Additionally, it becomes complicated
because observers could insert additional children, making it harder
(aka more expensive) to determine which children are dupes and which are
not.

The path I chose is to support "opting out" of the relationship target
hook in the contexts that need that, as this allows us to just cheaply
clone the mapped collection. The relationship hook can look for this
configuration when it runs and skip its logic when that happens. A
"simple" / small-amount-of-code way to do this would be to add a "skip
relationship spawn" flag to World. Sadly, any hook / observer that runs
_as the result of an insert_ would also read this flag. We really need a
way to scope this setting to a _specific_ insert.

Therefore I opted to add a new `RelationshipInsertHookMode` enum and an
`entity.insert_with_relationship_insert_hook_mode` variant. Obviously
this is verbose and ugly. And nobody wants _more_ insert variants. But
sadly this was the best I could come up with from a performance and
capability perspective. If you have alternatives let me know!

There are three variants:

1. `RelationshipInsertHookMode::Run`: always run relationship insert
hooks (this is the default)
2. `RelationshipInsertHookMode::Skip`: do not run any relationship
insert hooks for this insert (this is used by spawner code)
3. `RelationshipInsertHookMode::RunIfNotLinked`: only run hooks for
_unlinked_ relationships (this is used in same-world recursive entity
cloning to preserve relationships outside of the deep-cloned tree)

Note that I have intentionally only added "insert with relationship hook
mode" variants to the cases we absolutely need (everything else uses the
default `Run` mode), just to keep the code size in check. I do not think
we should add more without real _very necessary_ use cases.

I also made some other minor tweaks:

1. I split out `SourceComponent` from `ComponentCloneCtx`. Reading the
source component no longer needlessly blocks mutable access to
`ComponentCloneCtx`.
2. Thanks to (1), I've removed the `RefCell` wrapper over the cloned
component queue.
3. (1) also allowed me to write to the EntityMapper while queuing up
clones, meaning we can reserve entities during the component clone and
write them to the mapper _before_ inserting the component, meaning
cloned collections can be mapped on insert.
4. I've removed the closure from `write_target_component_ptr` to
simplify the API / make it compatible with the split `SourceComponent`
approach.
5. I've renamed `EntityCloner::recursive` to
`EntityCloner::linked_cloning` to connect that feature more directly
with `RelationshipTarget::LINKED_SPAWN`
6. I've removed `EntityCloneBehavior::RelationshipTarget`. This was
always intended to be temporary, and this new behavior removes the need
for it.

---------

Co-authored-by: Viktor Gustavsson <villor94@gmail.com>
2025-03-05 22:18:57 +00:00
Chris Russell
1f6642df4c
Fix unsound query transmutes on queries obtained from Query::as_readonly() (#17973)
# Objective

Fix unsound query transmutes on queries obtained from
`Query::as_readonly()`.

The following compiles, and the call to `transmute_lens()` should panic,
but does not:
```rust
fn bad_system(query: Query<&mut A>) {
    let mut readonly = query.as_readonly();
    let mut lens: QueryLens<&mut A> = readonly.transmute_lens();
    let other_readonly: Query<&A> = query.as_readonly();
    // `lens` and `other_readonly` alias, and are both alive here!
}
```

To make `Query::as_readonly()` zero-cost, we pointer-cast
`&QueryState<D, F>` to `&QueryState<D::ReadOnly, F>`. This means that
the `component_access` for a read-only query's state may include
accesses for the original mutable version, but the `Query` does not have
exclusive access to those components! `transmute` and `join` use that
access to ensure that a join is valid, and will incorrectly allow a
transmute that includes mutable access.

As a bonus, allow `Query::join`s that output `FilteredEntityRef` or
`FilteredEntityMut` to receive access from the `other` query. Currently
they only receive access from `self`.

## Solution

When transmuting or joining from a read-only query, remove any writes
before performing checking that the transmute is valid. For joins, be
sure to handle the case where one input query was the result of
`as_readonly()` but the other has valid mutable access.

This requires identifying read-only queries, so add a
`QueryData::IS_READ_ONLY` associated constant. Note that we only call
`QueryState::as_transmuted_state()` with `NewD: ReadOnlyQueryData`, so
checking for read-only queries is sufficient to check for
`as_transmuted_state()`.

Removing writes requires allocating a new `FilteredAccess`, so only do
so if the query is read-only and the state has writes. Otherwise, the
existing access is correct and we can continue using a reference to it.

Use the new read-only state to call `NewD::set_access`, so that
transmuting to a `FilteredAccessMut` results in a read-only
`FilteredAccessMut`. Otherwise, it would take the original write access,
and then the transmute would panic because it had too much access.

Note that `join` was previously passing `self.component_access` to
`NewD::set_access`. Switching it to `joined_component_access` also
allows a join that outputs `FilteredEntity(Ref|Mut)` to receive access
from `other`. The fact that it didn't do that before seems like an
oversight, so I didn't try to prevent that change.

## Testing

Added unit tests with the unsound transmute and join.
2025-03-04 19:26:31 +00:00
Tim Overbeek
173680944f
fix generics for relationships (#18136)
# Objective
Allow Relationship to be derived for structs with generics.

fixes #18133
## Solution

"X" inside #[relationship_target(relationship = X)] was previously
parsed as Idents,
now they are parsed as syn::Type

## Testing

```rust
#[derive(Component)]
#[relationship(relationship_target = Attachments<T>)]
pub struct AttachedTo<T: Send + Sync + 'static> {
    #[relationship]
    pub entity: Entity,
    pub marker: PhantomData<T>,
}

#[derive(Component)]
#[relationship_target(relationship = AttachedTo<T>)]
pub struct Attachments<T: Send + Sync + 'static> {
    #[relationship]
    entities: Vec<Entity>,
    pub marker: PhantomData<T>,
}
```
This now compiles!
2025-03-03 19:33:29 +00:00
Tim Overbeek
ccb7069e7f
Change ChildOf to Childof { parent: Entity} and support deriving Relationship and RelationshipTarget with named structs (#17905)
# Objective

fixes #17896 

## Solution

Change ChildOf ( Entity ) to ChildOf { parent: Entity }

by doing this we also allow users to use named structs for relationship
derives, When you have more than 1 field in a struct with named fields
the macro will look for a field with the attribute #[relationship] and
all of the other fields should implement the Default trait. Unnamed
fields are still supported.

When u have a unnamed struct with more than one field the macro will
fail.
Do we want to support something like this ? 

```rust
 #[derive(Component)]
 #[relationship_target(relationship = ChildOf)]
 pub struct Children (#[relationship] Entity, u8);
```
I could add this, it but doesn't seem nice.
## Testing

crates/bevy_ecs - cargo test


## Showcase


```rust

use bevy_ecs::component::Component;
use bevy_ecs::entity::Entity;

 #[derive(Component)]
 #[relationship(relationship_target = Children)]
 pub struct ChildOf {
     #[relationship]
     pub parent: Entity,
     internal: u8,
 };

 #[derive(Component)]
 #[relationship_target(relationship = ChildOf)]
 pub struct Children {
     children: Vec<Entity>
 };

```

---------

Co-authored-by: Tim Overbeek <oorbecktim@Tims-MacBook-Pro.local>
Co-authored-by: Tim Overbeek <oorbecktim@c-001-001-042.client.nl.eduvpn.org>
Co-authored-by: Tim Overbeek <oorbecktim@c-001-001-059.client.nl.eduvpn.org>
Co-authored-by: Tim Overbeek <oorbecktim@c-001-001-054.client.nl.eduvpn.org>
Co-authored-by: Tim Overbeek <oorbecktim@c-001-001-027.client.nl.eduvpn.org>
2025-02-27 19:22:17 +00:00
Zachary Harrold
5241e09671
Upgrade to Rust Edition 2024 (#17967)
# Objective

- Fixes #17960

## Solution

- Followed the [edition upgrade
guide](https://doc.rust-lang.org/edition-guide/editions/transitioning-an-existing-project-to-a-new-edition.html)

## Testing

- CI

---

## Summary of Changes

### Documentation Indentation

When using lists in documentation, proper indentation is now linted for.
This means subsequent lines within the same list item must start at the
same indentation level as the item.

```rust
/* Valid */
/// - Item 1
///   Run-on sentence.
/// - Item 2
struct Foo;

/* Invalid */
/// - Item 1
///     Run-on sentence.
/// - Item 2
struct Foo;
```

### Implicit `!` to `()` Conversion

`!` (the never return type, returned by `panic!`, etc.) no longer
implicitly converts to `()`. This is particularly painful for systems
with `todo!` or `panic!` statements, as they will no longer be functions
returning `()` (or `Result<()>`), making them invalid systems for
functions like `add_systems`. The ideal fix would be to accept functions
returning `!` (or rather, _not_ returning), but this is blocked on the
[stabilisation of the `!` type
itself](https://doc.rust-lang.org/std/primitive.never.html), which is
not done.

The "simple" fix would be to add an explicit `-> ()` to system
signatures (e.g., `|| { todo!() }` becomes `|| -> () { todo!() }`).
However, this is _also_ banned, as there is an existing lint which (IMO,
incorrectly) marks this as an unnecessary annotation.

So, the "fix" (read: workaround) is to put these kinds of `|| -> ! { ...
}` closuers into variables and give the variable an explicit type (e.g.,
`fn()`).

```rust
// Valid
let system: fn() = || todo!("Not implemented yet!");
app.add_systems(..., system);

// Invalid
app.add_systems(..., || todo!("Not implemented yet!"));
```

### Temporary Variable Lifetimes

The order in which temporary variables are dropped has changed. The
simple fix here is _usually_ to just assign temporaries to a named
variable before use.

### `gen` is a keyword

We can no longer use the name `gen` as it is reserved for a future
generator syntax. This involved replacing uses of the name `gen` with
`r#gen` (the raw-identifier syntax).

### Formatting has changed

Use statements have had the order of imports changed, causing a
substantial +/-3,000 diff when applied. For now, I have opted-out of
this change by amending `rustfmt.toml`

```toml
style_edition = "2021"
```

This preserves the original formatting for now, reducing the size of
this PR. It would be a simple followup to update this to 2024 and run
`cargo fmt`.

### New `use<>` Opt-Out Syntax

Lifetimes are now implicitly included in RPIT types. There was a handful
of instances where it needed to be added to satisfy the borrow checker,
but there may be more cases where it _should_ be added to avoid
breakages in user code.

### `MyUnitStruct { .. }` is an invalid pattern

Previously, you could match against unit structs (and unit enum
variants) with a `{ .. }` destructuring. This is no longer valid.

### Pretty much every use of `ref` and `mut` are gone

Pattern binding has changed to the point where these terms are largely
unused now. They still serve a purpose, but it is far more niche now.

### `iter::repeat(...).take(...)` is bad

New lint recommends using the more explicit `iter::repeat_n(..., ...)`
instead.

## Migration Guide

The lifetimes of functions using return-position impl-trait (RPIT) are
likely _more_ conservative than they had been previously. If you
encounter lifetime issues with such a function, please create an issue
to investigate the addition of `+ use<...>`.

## Notes

- Check the individual commits for a clearer breakdown for what
_actually_ changed.

---------

Co-authored-by: François Mockers <francois.mockers@vleue.com>
2025-02-24 03:54:47 +00:00
person93
575f66504b
Silence deprecation warning in Bundle derive macro (#17369) (#17790)
# Objective

- Fixes #17369

## Solution

- Add `#[allow(deprecated)]` to the generated code.
2025-02-11 00:56:09 +00:00
Carter Anderson
ea578415e1
Improved Spawn APIs and Bundle Effects (#17521)
## Objective

A major critique of Bevy at the moment is how boilerplatey it is to
compose (and read) entity hierarchies:

```rust
commands
    .spawn(Foo)
    .with_children(|p| {
        p.spawn(Bar).with_children(|p| {
            p.spawn(Baz);
        });
        p.spawn(Bar).with_children(|p| {
            p.spawn(Baz);
        });
    });
```

There is also currently no good way to statically define and return an
entity hierarchy from a function. Instead, people often do this
"internally" with a Commands function that returns nothing, making it
impossible to spawn the hierarchy in other cases (direct World spawns,
ChildSpawner, etc).

Additionally, because this style of API results in creating the
hierarchy bits _after_ the initial spawn of a bundle, it causes ECS
archetype changes (and often expensive table moves).

Because children are initialized after the fact, we also can't count
them to pre-allocate space. This means each time a child inserts itself,
it has a high chance of overflowing the currently allocated capacity in
the `RelationshipTarget` collection, causing literal worst-case
reallocations.

We can do better!

## Solution

The Bundle trait has been extended to support an optional
`BundleEffect`. This is applied directly to World immediately _after_
the Bundle has fully inserted. Note that this is
[intentionally](https://github.com/bevyengine/bevy/discussions/16920)
_not done via a deferred Command_, which would require repeatedly
copying each remaining subtree of the hierarchy to a new command as we
walk down the tree (_not_ good performance).

This allows us to implement the new `SpawnRelated` trait for all
`RelationshipTarget` impls, which looks like this in practice:

```rust
world.spawn((
    Foo,
    Children::spawn((
        Spawn((
            Bar,
            Children::spawn(Spawn(Baz)),
        )),
        Spawn((
            Bar,
            Children::spawn(Spawn(Baz)),
        )),
    ))
))
```

`Children::spawn` returns `SpawnRelatedBundle<Children, L:
SpawnableList>`, which is a `Bundle` that inserts `Children`
(preallocated to the size of the `SpawnableList::size_hint()`).
`Spawn<B: Bundle>(pub B)` implements `SpawnableList` with a size of 1.
`SpawnableList` is also implemented for tuples of `SpawnableList` (same
general pattern as the Bundle impl).

There are currently three built-in `SpawnableList` implementations:

```rust
world.spawn((
    Foo,
    Children::spawn((
        Spawn(Name::new("Child1")),   
        SpawnIter(["Child2", "Child3"].into_iter().map(Name::new),
        SpawnWith(|parent: &mut ChildSpawner| {
            parent.spawn(Name::new("Child4"));
            parent.spawn(Name::new("Child5"));
        })
    )),
))
```

We get the benefits of "structured init", but we have nice flexibility
where it is required!

Some readers' first instinct might be to try to remove the need for the
`Spawn` wrapper. This is impossible in the Rust type system, as a tuple
of "child Bundles to be spawned" and a "tuple of Components to be added
via a single Bundle" is ambiguous in the Rust type system. There are two
ways to resolve that ambiguity:

1. By adding support for variadics to the Rust type system (removing the
need for nested bundles). This is out of scope for this PR :)
2. Using wrapper types to resolve the ambiguity (this is what I did in
this PR).

For the single-entity spawn cases, `Children::spawn_one` does also
exist, which removes the need for the wrapper:

```rust
world.spawn((
    Foo,
    Children::spawn_one(Bar),
))
```

## This works for all Relationships

This API isn't just for `Children` / `ChildOf` relationships. It works
for any relationship type, and they can be mixed and matched!

```rust
world.spawn((
    Foo,
    Observers::spawn((
        Spawn(Observer::new(|trigger: Trigger<FuseLit>| {})),
        Spawn(Observer::new(|trigger: Trigger<Exploded>| {})),
    )),
    OwnerOf::spawn(Spawn(Bar))
    Children::spawn(Spawn(Baz))
))
```

## Macros

While `Spawn` is necessary to satisfy the type system, we _can_ remove
the need to express it via macros. The example above can be expressed
more succinctly using the new `children![X]` macro, which internally
produces `Children::spawn(Spawn(X))`:

```rust
world.spawn((
    Foo,
    children![
        (
            Bar,
            children![Baz],
        ),
        (
            Bar,
            children![Baz],
        ),
    ]
))
```

There is also a `related!` macro, which is a generic version of the
`children!` macro that supports any relationship type:

```rust
world.spawn((
    Foo,
    related!(Children[
        (
            Bar,
            related!(Children[Baz]),
        ),
        (
            Bar,
            related!(Children[Baz]),
        ),
    ])
))
```

## Returning Hierarchies from Functions

Thanks to these changes, the following pattern is now possible:

```rust
fn button(text: &str, color: Color) -> impl Bundle {
    (
        Node {
            width: Val::Px(300.),
            height: Val::Px(100.),
            ..default()
        },
        BackgroundColor(color),
        children![
            Text::new(text),
        ]
    )
}

fn ui() -> impl Bundle {
    (
        Node {
            width: Val::Percent(100.0),
            height: Val::Percent(100.0),
            ..default(),
        },
        children![
            button("hello", BLUE),
            button("world", RED),
        ]
    )
}

// spawn from a system
fn system(mut commands: Commands) {
    commands.spawn(ui());
}

// spawn directly on World
world.spawn(ui());
```

## Additional Changes and Notes

* `Bundle::from_components` has been split out into
`BundleFromComponents::from_components`, enabling us to implement
`Bundle` for types that cannot be "taken" from the ECS (such as the new
`SpawnRelatedBundle`).
* The `NoBundleEffect` trait (which implements `BundleEffect`) is
implemented for empty tuples (and tuples of empty tuples), which allows
us to constrain APIs to only accept bundles that do not have effects.
This is critical because the current batch spawn APIs cannot efficiently
apply BundleEffects in their current form (as doing so in-place could
invalidate the cached raw pointers). We could consider allocating a
buffer of the effects to be applied later, but that does have
performance implications that could offset the balance and value of the
batched APIs (and would likely require some refactors to the underlying
code). I've decided to be conservative here. We can consider relaxing
that requirement on those APIs later, but that should be done in a
followup imo.
* I've ported a few examples to illustrate real-world usage. I think in
a followup we should port all examples to the `children!` form whenever
possible (and for cases that require things like SpawnIter, use the raw
APIs).
* Some may ask "why not use the `Relationship` to spawn (ex:
`ChildOf::spawn(Foo)`) instead of the `RelationshipTarget` (ex:
`Children::spawn(Spawn(Foo))`)?". That _would_ allow us to remove the
`Spawn` wrapper. I've explicitly chosen to disallow this pattern.
`Bundle::Effect` has the ability to create _significant_ weirdness.
Things in `Bundle` position look like components. For example
`world.spawn((Foo, ChildOf::spawn(Bar)))` _looks and reads_ like Foo is
a child of Bar. `ChildOf` is in Foo's "component position" but it is not
a component on Foo. This is a huge problem. Now that `Bundle::Effect`
exists, we should be _very_ principled about keeping the "weird and
unintuitive behavior" to a minimum. Things that read like components
_should be the components they appear to be".

## Remaining Work

* The macros are currently trivially implemented using macro_rules and
are currently limited to the max tuple length. They will require a
proc_macro implementation to work around the tuple length limit.

## Next Steps

* Port the remaining examples to use `children!` where possible and raw
`Spawn` / `SpawnIter` / `SpawnWith` where the flexibility of the raw API
is required.

## Migration Guide

Existing spawn patterns will continue to work as expected.

Manual Bundle implementations now require a `BundleEffect` associated
type. Exisiting bundles would have no bundle effect, so use `()`.
Additionally `Bundle::from_components` has been moved to the new
`BundleFromComponents` trait.

```rust
// Before
unsafe impl Bundle for X {
    unsafe fn from_components<T, F>(ctx: &mut T, func: &mut F) -> Self {
    }
    /* remaining bundle impl here */
}

// After
unsafe impl Bundle for X {
    type Effect = ();
    /* remaining bundle impl here */
}

unsafe impl BundleFromComponents for X {
    unsafe fn from_components<T, F>(ctx: &mut T, func: &mut F) -> Self {
    }
}
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Gino Valente <49806985+MrGVSV@users.noreply.github.com>
Co-authored-by: Emerson Coskey <emerson@coskey.dev>
2025-02-09 23:32:56 +00:00
François Mockers
7400e7adfd
Cleanup publish process (#17728)
# Objective

- publish script copy the license files to all subcrates, meaning that
all publish are dirty. this breaks git verification of crates
- the order and list of crates to publish is manually maintained,
leading to error. cargo 1.84 is more strict and the list is currently
wrong

## Solution

- duplicate all the licenses to all crates and remove the
`--allow-dirty` flag
- instead of a manual list of crates, get it from `cargo package
--workspace`
- remove the `--no-verify` flag to... verify more things?
2025-02-09 17:46:19 +00:00
Carter Anderson
3c8fae2390
Improved Entity Mapping and Cloning (#17687)
Fixes #17535

Bevy's approach to handling "entity mapping" during spawning and cloning
needs some work. The addition of
[Relations](https://github.com/bevyengine/bevy/pull/17398) both
[introduced a new "duplicate entities" bug when spawning scenes in the
scene system](#17535) and made the weaknesses of the current mapping
system exceedingly clear:

1. Entity mapping requires _a ton_ of boilerplate (implement or derive
VisitEntities and VisitEntitesMut, then register / reflect MapEntities).
Knowing the incantation is challenging and if you forget to do it in
part or in whole, spawning subtly breaks.
2. Entity mapping a spawned component in scenes incurs unnecessary
overhead: look up ReflectMapEntities, create a _brand new temporary
instance_ of the component using FromReflect, map the entities in that
instance, and then apply that on top of the actual component using
reflection. We can do much better.

Additionally, while our new [Entity cloning
system](https://github.com/bevyengine/bevy/pull/16132) is already pretty
great, it has some areas we can make better:

* It doesn't expose semantic info about the clone (ex: ignore or "clone
empty"), meaning we can't key off of that in places where it would be
useful, such as scene spawning. Rather than duplicating this info across
contexts, I think it makes more sense to add that info to the clone
system, especially given that we'd like to use cloning code in some of
our spawning scenarios.
* EntityCloner is currently built in a way that prioritizes a single
entity clone
* EntityCloner's recursive cloning is built to be done "inside out" in a
parallel context (queue commands that each have a clone of
EntityCloner). By making EntityCloner the orchestrator of the clone we
can remove internal arcs, improve the clarity of the code, make
EntityCloner mutable again, and simplify the builder code.
* EntityCloner does not currently take into account entity mapping. This
is necessary to do true "bullet proof" cloning, would allow us to unify
the per-component scene spawning and cloning UX, and ultimately would
allow us to use EntityCloner in place of raw reflection for scenes like
`Scene(World)` (which would give us a nice performance boost: fewer
archetype moves, less reflection overhead).

## Solution

### Improved Entity Mapping

First, components now have first-class "entity visiting and mapping"
behavior:

```rust
#[derive(Component, Reflect)]
#[reflect(Component)]
struct Inventory {
    size: usize,
    #[entities]
    items: Vec<Entity>,
}
```

Any field with the `#[entities]` annotation will be viewable and
mappable when cloning and spawning scenes.

Compare that to what was required before!

```rust
#[derive(Component, Reflect, VisitEntities, VisitEntitiesMut)]
#[reflect(Component, MapEntities)]
struct Inventory {
    #[visit_entities(ignore)]
    size: usize,
    items: Vec<Entity>,
}
```

Additionally, for relationships `#[entities]` is implied, meaning this
"just works" in scenes and cloning:

```rust
#[derive(Component, Reflect)]
#[relationship(relationship_target = Children)]
#[reflect(Component)]
struct ChildOf(pub Entity);
```

Note that Component _does not_ implement `VisitEntities` directly.
Instead, it has `Component::visit_entities` and
`Component::visit_entities_mut` methods. This is for a few reasons:

1. We cannot implement `VisitEntities for C: Component` because that
would conflict with our impl of VisitEntities for anything that
implements `IntoIterator<Item=Entity>`. Preserving that impl is more
important from a UX perspective.
2. We should not implement `Component: VisitEntities` VisitEntities in
the Component derive, as that would increase the burden of manual
Component trait implementors.
3. Making VisitEntitiesMut directly callable for components would make
it easy to invalidate invariants defined by a component author. By
putting it in the `Component` impl, we can make it harder to call
naturally / unavailable to autocomplete using `fn
visit_entities_mut(this: &mut Self, ...)`.

`ReflectComponent::apply_or_insert` is now
`ReflectComponent::apply_or_insert_mapped`. By moving mapping inside
this impl, we remove the need to go through the reflection system to do
entity mapping, meaning we no longer need to create a clone of the
target component, map the entities in that component, and patch those
values on top. This will make spawning mapped entities _much_ faster
(The default `Component::visit_entities_mut` impl is an inlined empty
function, so it will incur no overhead for unmapped entities).

### The Bug Fix

To solve #17535, spawning code now skips entities with the new
`ComponentCloneBehavior::Ignore` and
`ComponentCloneBehavior::RelationshipTarget` variants (note
RelationshipTarget is a temporary "workaround" variant that allows
scenes to skip these components. This is a temporary workaround that can
be removed as these cases should _really_ be using EntityCloner logic,
which should be done in a followup PR. When that is done,
`ComponentCloneBehavior::RelationshipTarget` can be merged into the
normal `ComponentCloneBehavior::Custom`).

### Improved Cloning

* `Option<ComponentCloneHandler>` has been replaced by
`ComponentCloneBehavior`, which encodes additional intent and context
(ex: `Default`, `Ignore`, `Custom`, `RelationshipTarget` (this last one
is temporary)).
* Global per-world entity cloning configuration has been removed. This
felt overly complicated, increased our API surface, and felt too
generic. Each clone context can have different requirements (ex: what a
user wants in a specific system, what a scene spawner wants, etc). I'd
prefer to see how far context-specific EntityCloners get us first.
* EntityCloner's internals have been reworked to remove Arcs and make it
mutable.
* EntityCloner is now directly stored on EntityClonerBuilder,
simplifying the code somewhat
* EntityCloner's "bundle scratch" pattern has been moved into the new
BundleScratch type, improving its usability and making it usable in
other contexts (such as future cross-world cloning code). Currently this
is still private, but with some higher level safe APIs it could be used
externally for making dynamic bundles
* EntityCloner's recursive cloning behavior has been "externalized". It
is now responsible for orchestrating recursive clones, meaning it no
longer needs to be sharable/clone-able across threads / read-only.
* EntityCloner now does entity mapping during clones, like scenes do.
This gives behavior parity and also makes it more generically useful.
* `RelatonshipTarget::RECURSIVE_SPAWN` is now
`RelationshipTarget::LINKED_SPAWN`, and this field is used when cloning
relationship targets to determine if cloning should happen recursively.
The new `LINKED_SPAWN` term was picked to make it more generically
applicable across spawning and cloning scenarios.

## Next Steps

* I think we should adapt EntityCloner to support cross world cloning. I
think this PR helps set the stage for that by making the internals
slightly more generalized. We could have a CrossWorldEntityCloner that
reuses a lot of this infrastructure.
* Once we support cross world cloning, we should use EntityCloner to
spawn `Scene(World)` scenes. This would yield significant performance
benefits (no archetype moves, less reflection overhead).

---------

Co-authored-by: eugineerd <70062110+eugineerd@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-02-06 22:13:41 +00:00
ElliottjPierce
1b2cf7d6cd
Isolate component registration (#17671)
# Objective

Progresses #17569. The end goal here is to synchronize component
registration. See the other PR for details for the motivation behind
that.

For this PR specifically, the objective is to decouple `Components` from
`Storages`. What components are registered etc should have nothing to do
with what Storages looks like. Storages should only care about what
entity archetypes have been spawned.

## Solution

Previously, this was used to create sparse sets for relevant components
when those components were registered. Now, we do that when the
component is inserted/spawned.

This PR proposes doing that in `BundleInfo::new`, but there may be a
better place.

## Testing

In theory, this shouldn't have changed any functionality, so no new
tests were created. I'm not aware of any examples that make heavy use of
sparse set components either.

## Migration Guide

- Remove storages from functions where it is no longer needed.
- Note that SparseSets are no longer present for all registered sparse
set components, only those that have been spawned.

---------

Co-authored-by: SpecificProtagonist <vincentjunge@posteo.net>
Co-authored-by: Chris Russell <8494645+chescock@users.noreply.github.com>
2025-02-05 19:59:30 +00:00
Zachary Harrold
d0c0bad7b4
Split Component::register_component_hooks into individual methods (#17685)
# Objective

- Fixes #17411

## Solution

- Deprecated `Component::register_component_hooks`
- Added individual methods for each hook which return `None` if the hook
is unused.

## Testing

- CI

---

## Migration Guide

`Component::register_component_hooks` is now deprecated and will be
removed in a future release. When implementing `Component` manually,
also implement the respective hook methods on `Component`.

```rust
// Before
impl Component for Foo {
    // snip
    fn register_component_hooks(hooks: &mut ComponentHooks) {
            hooks.on_add(foo_on_add);
    }
}

// After
impl Component for Foo {
    // snip
    fn on_add() -> Option<ComponentHook> {
            Some(foo_on_add)
    }
}
```

## Notes

I've chosen to deprecate `Component::register_component_hooks` rather
than outright remove it to ease the migration guide. While it is in a
state of deprecation, it must be used by
`Components::register_component_internal` to ensure users who haven't
migrated to the new hook definition scheme aren't left behind. For users
of the new scheme, a default implementation of
`Component::register_component_hooks` is provided which forwards the new
individual hook implementations.

Personally, I think this is a cleaner API to work with, and would allow
the documentation for hooks to exist on the respective `Component`
methods (e.g., documentation for `OnAdd` can exist on
`Component::on_add`). Ideally, `Component::on_add` would be the hook
itself rather than a getter for the hook, but it is the only way to
early-out for a no-op hook, which is important for performance.

## Migration Guide

`Component::register_component_hooks` has been deprecated. If you are
manually implementing the `Component` trait and registering hooks there,
use the individual methods such as `on_add` instead for increased
clarity.
2025-02-05 19:33:05 +00:00
couyit
03af547c28
Move Item and fetch to QueryData from WorldQuery (#17679)
# Objective

Fixes #17662

## Solution

Moved `Item` and `fetch` from `WorldQuery` to `QueryData`, and adjusted
their implementations accordingly.

Currently, documentation related to `fetch` is written under
`WorldQuery`. It would be more appropriate to move it to the `QueryData`
documentation for clarity.

I am not very experienced with making contributions. If there are any
mistakes or areas for improvement, I would appreciate any suggestions
you may have.

## Migration Guide

The `WorldQuery::Item` type and `WorldQuery::fetch` method have been
moved to `QueryData`, as they were not useful for `QueryFilter` types.

---------

Co-authored-by: Chris Russell <8494645+chescock@users.noreply.github.com>
2025-02-05 18:46:18 +00:00
Tim Overbeek
eb04f8a476
Simplify derive_from_world (#17534)
# Objective

simplify existing implementation

---------

Co-authored-by: Gino Valente <49806985+MrGVSV@users.noreply.github.com>
2025-01-26 22:25:29 +00:00
Tim Overbeek
da57dfb62f
DeriveWorld for enums (#17496)
# Objective

Fixes #17457 

## Solution

#[derive(FromWorld)] now works with enums by specifying which variant
should be used.

## Showcase

```rust
#[Derive(FromWorld)]
enum Game {
    #[from_world]
    Playing, 
    Stopped
}
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: Benjamin Brienen <benjamin.brienen@outlook.com>
2025-01-23 04:06:00 +00:00
Alice Cecile
44ad3bf62b
Move Resource trait to its own file (#17469)
# Objective

`bevy_ecs`'s `system` module is something of a grab bag, and *very*
large. This is particularly true for the `system_param` module, which is
more than 2k lines long!

While it could be defensible to put `Res` and `ResMut` there (lol no
they're in change_detection.rs, obviously), it doesn't make any sense to
put the `Resource` trait there. This is confusing to navigate (and
painful to work on and review).

## Solution

- Create a root level `bevy_ecs/resource.rs` module to mirror
`bevy_ecs/component.rs`
- move the `Resource` trait to that module
- move the `Resource` derive macro to that module as well (Rust really
likes when you pun on the names of the derive macro and trait and put
them in the same path)
- fix all of the imports

## Notes to reviewers

- We could probably move more stuff into here, but I wanted to keep this
PR as small as possible given the absurd level of import changes.
- This PR is ground work for my upcoming attempts to store resource data
on components (resources-as-entities). Splitting this code out will make
the work and review a bit easier, and is the sort of overdue refactor
that's good to do as part of more meaningful work.

## Testing

cargo build works!

## Migration Guide

`bevy_ecs::system::Resource` has been moved to
`bevy_ecs::resource::Resource`.
2025-01-21 19:47:08 +00:00
Emerson Coskey
a99674ab86
FromWorld derive macro (#17352)
simple derive macro for `FromWorld`. Going to be needed for composable
pipeline specializers but probably a nice thing to have regardless

## Testing

simple manual testing, nothing seemed to blow up. I'm no proc macro pro
though, so there's a chance I've mishandled spans somewhere or
something.
2025-01-20 20:51:30 +00:00
Carter Anderson
21f1e3045c
Relationships (non-fragmenting, one-to-many) (#17398)
This adds support for one-to-many non-fragmenting relationships (with
planned paths for fragmenting and non-fragmenting many-to-many
relationships). "Non-fragmenting" means that entities with the same
relationship type, but different relationship targets, are not forced
into separate tables (which would cause "table fragmentation").

Functionally, this fills a similar niche as the current Parent/Children
system. The biggest differences are:

1. Relationships have simpler internals and significantly improved
performance and UX. Commands and specialized APIs are no longer
necessary to keep everything in sync. Just spawn entities with the
relationship components you want and everything "just works".
2. Relationships are generalized. Bevy can provide additional built in
relationships, and users can define their own.

**REQUEST TO REVIEWERS**: _please don't leave top level comments and
instead comment on specific lines of code. That way we can take
advantage of threaded discussions. Also dont leave comments simply
pointing out CI failures as I can read those just fine._

## Built on top of what we have

Relationships are implemented on top of the Bevy ECS features we already
have: components, immutability, and hooks. This makes them immediately
compatible with all of our existing (and future) APIs for querying,
spawning, removing, scenes, reflection, etc. The fewer specialized APIs
we need to build, maintain, and teach, the better.

## Why focus on one-to-many non-fragmenting first?

1. This allows us to improve Parent/Children relationships immediately,
in a way that is reasonably uncontroversial. Switching our hierarchy to
fragmenting relationships would have significant performance
implications. ~~Flecs is heavily considering a switch to non-fragmenting
relations after careful considerations of the performance tradeoffs.~~
_(Correction from @SanderMertens: Flecs is implementing non-fragmenting
storage specialized for asset hierarchies, where asset hierarchies are
many instances of small trees that have a well defined structure)_
2. Adding generalized one-to-many relationships is currently a priority
for the [Next Generation Scene / UI
effort](https://github.com/bevyengine/bevy/discussions/14437).
Specifically, we're interested in building reactions and observers on
top.

## The changes

This PR does the following:

1. Adds a generic one-to-many Relationship system
3. Ports the existing Parent/Children system to Relationships, which now
lives in `bevy_ecs::hierarchy`. The old `bevy_hierarchy` crate has been
removed.
4. Adds on_despawn component hooks
5. Relationships can opt-in to "despawn descendants" behavior, meaning
that the entire relationship hierarchy is despawned when
`entity.despawn()` is called. The built in Parent/Children hierarchies
enable this behavior, and `entity.despawn_recursive()` has been removed.
6. `world.spawn` now applies commands after spawning. This ensures that
relationship bookkeeping happens immediately and removes the need to
manually flush. This is in line with the equivalent behaviors recently
added to the other APIs (ex: insert).
7. Removes the ValidParentCheckPlugin (system-driven / poll based) in
favor of a `validate_parent_has_component` hook.

## Using Relationships

The `Relationship` trait looks like this:

```rust
pub trait Relationship: Component + Sized {
    type RelationshipSources: RelationshipSources<Relationship = Self>;
    fn get(&self) -> Entity;
    fn from(entity: Entity) -> Self;
}
```

A relationship is a component that:

1. Is a simple wrapper over a "target" Entity.
2. Has a corresponding `RelationshipSources` component, which is a
simple wrapper over a collection of entities. Every "target entity"
targeted by a "source entity" with a `Relationship` has a
`RelationshipSources` component, which contains every "source entity"
that targets it.

For example, the `Parent` component (as it currently exists in Bevy) is
the `Relationship` component and the entity containing the Parent is the
"source entity". The entity _inside_ the `Parent(Entity)` component is
the "target entity". And that target entity has a `Children` component
(which implements `RelationshipSources`).

In practice, the Parent/Children relationship looks like this:

```rust
#[derive(Relationship)]
#[relationship(relationship_sources = Children)]
pub struct Parent(pub Entity);

#[derive(RelationshipSources)]
#[relationship_sources(relationship = Parent)]
pub struct Children(Vec<Entity>);
```

The Relationship and RelationshipSources derives automatically implement
Component with the relevant configuration (namely, the hooks necessary
to keep everything in sync).

The most direct way to add relationships is to spawn entities with
relationship components:

```rust
let a = world.spawn_empty().id();
let b = world.spawn(Parent(a)).id();

assert_eq!(world.entity(a).get::<Children>().unwrap(), &[b]);
```

There are also convenience APIs for spawning more than one entity with
the same relationship:

```rust
world.spawn_empty().with_related::<Children>(|s| {
    s.spawn_empty();
    s.spawn_empty();
})
```

The existing `with_children` API is now a simpler wrapper over
`with_related`. This makes this change largely non-breaking for existing
spawn patterns.

```rust
world.spawn_empty().with_children(|s| {
    s.spawn_empty();
    s.spawn_empty();
})
```

There are also other relationship APIs, such as `add_related` and
`despawn_related`.

## Automatic recursive despawn via the new on_despawn hook

`RelationshipSources` can opt-in to "despawn descendants" behavior,
which will despawn all related entities in the relationship hierarchy:

```rust
#[derive(RelationshipSources)]
#[relationship_sources(relationship = Parent, despawn_descendants)]
pub struct Children(Vec<Entity>);
```

This means that `entity.despawn_recursive()` is no longer required.
Instead, just use `entity.despawn()` and the relevant related entities
will also be despawned.

To despawn an entity _without_ despawning its parent/child descendants,
you should remove the `Children` component first, which will also remove
the related `Parent` components:

```rust
entity
    .remove::<Children>()
    .despawn()
```

This builds on the on_despawn hook introduced in this PR, which is fired
when an entity is despawned (before other hooks).

## Relationships are the source of truth

`Relationship` is the _single_ source of truth component.
`RelationshipSources` is merely a reflection of what all the
`Relationship` components say. By embracing this, we are able to
significantly improve the performance of the system as a whole. We can
rely on component lifecycles to protect us against duplicates, rather
than needing to scan at runtime to ensure entities don't already exist
(which results in quadratic runtime). A single source of truth gives us
constant-time inserts. This does mean that we cannot directly spawn
populated `Children` components (or directly add or remove entities from
those components). I personally think this is a worthwhile tradeoff,
both because it makes the performance much better _and_ because it means
theres exactly one way to do things (which is a philosophy we try to
employ for Bevy APIs).

As an aside: treating both sides of the relationship as "equivalent
source of truth relations" does enable building simple and flexible
many-to-many relationships. But this introduces an _inherent_ need to
scan (or hash) to protect against duplicates.
[`evergreen_relations`](https://github.com/EvergreenNest/evergreen_relations)
has a very nice implementation of the "symmetrical many-to-many"
approach. Unfortunately I think the performance issues inherent to that
approach make it a poor choice for Bevy's default relationship system.

## Followup Work

* Discuss renaming `Parent` to `ChildOf`. I refrained from doing that in
this PR to keep the diff reasonable, but I'm personally biased toward
this change (and using that naming pattern generally for relationships).
* [Improved spawning
ergonomics](https://github.com/bevyengine/bevy/discussions/16920)
* Consider adding relationship observers/triggers for "relationship
targets" whenever a source is added or removed. This would replace the
current "hierarchy events" system, which is unused upstream but may have
existing users downstream. I think triggers are the better fit for this
than a buffered event queue, and would prefer not to add that back.
* Fragmenting relations: My current idea hinges on the introduction of
"value components" (aka: components whose type _and_ value determines
their ComponentId, via something like Hashing / PartialEq). By labeling
a Relationship component such as `ChildOf(Entity)` as a "value
component", `ChildOf(e1)` and `ChildOf(e2)` would be considered
"different components". This makes the transition between fragmenting
and non-fragmenting a single flag, and everything else continues to work
as expected.
* Many-to-many support
* Non-fragmenting: We can expand Relationship to be a list of entities
instead of a single entity. I have largely already written the code for
this.
* Fragmenting: With the "value component" impl mentioned above, we get
many-to-many support "for free", as it would allow inserting multiple
copies of a Relationship component with different target entities.

Fixes #3742 (If this PR is merged, I think we should open more targeted
followup issues for the work above, with a fresh tracking issue free of
the large amount of less-directed historical context)
Fixes #17301
Fixes #12235 
Fixes #15299
Fixes #15308 

## Migration Guide

* Replace `ChildBuilder` with `ChildSpawnerCommands`.
* Replace calls to `.set_parent(parent_id)` with
`.insert(Parent(parent_id))`.
* Replace calls to `.replace_children()` with `.remove::<Children>()`
followed by `.add_children()`. Note that you'll need to manually despawn
any children that are not carried over.
* Replace calls to `.despawn_recursive()` with `.despawn()`.
* Replace calls to `.despawn_descendants()` with
`.despawn_related::<Children>()`.
* If you have any calls to `.despawn()` which depend on the children
being preserved, you'll need to remove the `Children` component first.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-01-18 22:20:30 +00:00