Commit Graph

19 Commits

Author SHA1 Message Date
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
Joona Aalto
7b1c9f192e
Adopt consistent FooSystems naming convention for system sets (#18900)
# Objective

Fixes a part of #14274.

Bevy has an incredibly inconsistent naming convention for its system
sets, both internally and across the ecosystem.

<img alt="System sets in Bevy"
src="https://github.com/user-attachments/assets/d16e2027-793f-4ba4-9cc9-e780b14a5a1b"
width="450" />

*Names of public system set types in Bevy*

Most Bevy types use a naming of `FooSystem` or just `Foo`, but there are
also a few `FooSystems` and `FooSet` types. In ecosystem crates on the
other hand, `FooSet` is perhaps the most commonly used name in general.
Conventions being so wildly inconsistent can make it harder for users to
pick names for their own types, to search for system sets on docs.rs, or
to even discern which types *are* system sets.

To reign in the inconsistency a bit and help unify the ecosystem, it
would be good to establish a common recommended naming convention for
system sets in Bevy itself, similar to how plugins are commonly suffixed
with `Plugin` (ex: `TimePlugin`). By adopting a consistent naming
convention in first-party Bevy, we can softly nudge ecosystem crates to
follow suit (for types where it makes sense to do so).

Choosing a naming convention is also relevant now, as the [`bevy_cli`
recently adopted
lints](https://github.com/TheBevyFlock/bevy_cli/pull/345) to enforce
naming for plugins and system sets, and the recommended naming used for
system sets is still a bit open.

## Which Name To Use?

Now the contentious part: what naming convention should we actually
adopt?

This was discussed on the Bevy Discord at the end of last year, starting
[here](<https://discord.com/channels/691052431525675048/692572690833473578/1310659954683936789>).
`FooSet` and `FooSystems` were the clear favorites, with `FooSet` very
narrowly winning an unofficial poll. However, it seems to me like the
consensus was broadly moving towards `FooSystems` at the end and after
the poll, with Cart
([source](https://discord.com/channels/691052431525675048/692572690833473578/1311140204974706708))
and later Alice
([source](https://discord.com/channels/691052431525675048/692572690833473578/1311092530732859533))
and also me being in favor of it.

Let's do a quick pros and cons list! Of course these are just what I
thought of, so take it with a grain of salt.

`FooSet`:

- Pro: Nice and short!
- Pro: Used by many ecosystem crates.
- Pro: The `Set` suffix comes directly from the trait name `SystemSet`.
- Pro: Pairs nicely with existing APIs like `in_set` and
`configure_sets`.
- Con: `Set` by itself doesn't actually indicate that it's related to
systems *at all*, apart from the implemented trait. A set of what?
- Con: Is `FooSet` a set of `Foo`s or a system set related to `Foo`? Ex:
`ContactSet`, `MeshSet`, `EnemySet`...

`FooSystems`:

- Pro: Very clearly indicates that the type represents a collection of
systems. The actual core concept, system(s), is in the name.
- Pro: Parallels nicely with `FooPlugins` for plugin groups.
- Pro: Low risk of conflicts with other names or misunderstandings about
what the type is.
- Pro: In most cases, reads *very* nicely and clearly. Ex:
`PhysicsSystems` and `AnimationSystems` as opposed to `PhysicsSet` and
`AnimationSet`.
- Pro: Easy to search for on docs.rs.
- Con: Usually results in longer names.
- Con: Not yet as widely used.

Really the big problem with `FooSet` is that it doesn't actually
describe what it is. It describes what *kind of thing* it is (a set of
something), but not *what it is a set of*, unless you know the type or
check its docs or implemented traits. `FooSystems` on the other hand is
much more self-descriptive in this regard, at the cost of being a bit
longer to type.

Ultimately, in some ways it comes down to preference and how you think
of system sets. Personally, I was originally in favor of `FooSet`, but
have been increasingly on the side of `FooSystems`, especially after
seeing what the new names would actually look like in Avian and now
Bevy. I prefer it because it usually reads better, is much more clearly
related to groups of systems than `FooSet`, and overall *feels* more
correct and natural to me in the long term.

For these reasons, and because Alice and Cart also seemed to share a
preference for it when it was previously being discussed, I propose that
we adopt a `FooSystems` naming convention where applicable.

## Solution

Rename Bevy's system set types to use a consistent `FooSet` naming where
applicable.

- `AccessibilitySystem` → `AccessibilitySystems`
- `GizmoRenderSystem` → `GizmoRenderSystems`
- `PickSet` → `PickingSystems`
- `RunFixedMainLoopSystem` → `RunFixedMainLoopSystems`
- `TransformSystem` → `TransformSystems`
- `RemoteSet` → `RemoteSystems`
- `RenderSet` → `RenderSystems`
- `SpriteSystem` → `SpriteSystems`
- `StateTransitionSteps` → `StateTransitionSystems`
- `RenderUiSystem` → `RenderUiSystems`
- `UiSystem` → `UiSystems`
- `Animation` → `AnimationSystems`
- `AssetEvents` → `AssetEventSystems`
- `TrackAssets` → `AssetTrackingSystems`
- `UpdateGizmoMeshes` → `GizmoMeshSystems`
- `InputSystem` → `InputSystems`
- `InputFocusSet` → `InputFocusSystems`
- `ExtractMaterialsSet` → `MaterialExtractionSystems`
- `ExtractMeshesSet` → `MeshExtractionSystems`
- `RumbleSystem` → `RumbleSystems`
- `CameraUpdateSystem` → `CameraUpdateSystems`
- `ExtractAssetsSet` → `AssetExtractionSystems`
- `Update2dText` → `Text2dUpdateSystems`
- `TimeSystem` → `TimeSystems`
- `AudioPlaySet` → `AudioPlaybackSystems`
- `SendEvents` → `EventSenderSystems`
- `EventUpdates` → `EventUpdateSystems`

A lot of the names got slightly longer, but they are also a lot more
consistent, and in my opinion the majority of them read much better. For
a few of the names I took the liberty of rewording things a bit;
definitely open to any further naming improvements.

There are still also cases where the `FooSystems` naming doesn't really
make sense, and those I left alone. This primarily includes system sets
like `Interned<dyn SystemSet>`, `EnterSchedules<S>`, `ExitSchedules<S>`,
or `TransitionSchedules<S>`, where the type has some special purpose and
semantics.

## Todo

- [x] Should I keep all the old names as deprecated type aliases? I can
do this, but to avoid wasting work I'd prefer to first reach consensus
on whether these renames are even desired.
- [x] Migration guide
- [x] Release notes
2025-05-06 15:18:03 +00:00
Hennadii Chernyshchyk
d82c359a5a
Add Default for all schedule labels (#18731)
# Objective

In `bevy_enhanced_input`, I'm trying to associate `Actions` with a
schedule. I can do this via an associated type on a trait, but there's
no way to construct the associated label except by requiring a `Default`
implementation. However, Bevy labels don't implement `Default`.

## Solution

Add `Default` to all built-in labels. I think it should be useful in
general.
2025-04-06 16:44:33 +00:00
Nick
d20f8553bf
Fix misleading documentation of Main schedule (#18579)
# Objective

Fixes #18562.

## Solution

- Specified that `StateTransition` is actually run before `PreStartup`.
- Specified consequences of this and how to actually run systems before
any game logic regardless of state.
- Updated docs of `StateTransition` to reflect that it is run before
`PreStartup` in addition to being run after `PreUpdate`.

## Testing

- `cargo doc`
- `cargo test --doc`
2025-03-28 01:12:19 +00:00
newclarityex
ecccd57417
Generic system config (#17962)
# Objective
Prevents duplicate implementation between IntoSystemConfigs and
IntoSystemSetConfigs using a generic, adds a NodeType trait for more
config flexibility (opening the door to implement
https://github.com/bevyengine/bevy/issues/14195?).

## Solution
Followed writeup by @ItsDoot:
https://hackmd.io/@doot/rJeefFHc1x

Removes IntoSystemConfigs and IntoSystemSetConfigs, instead using
IntoNodeConfigs with generics.

## Testing
Pending

---

## Showcase
N/A

## Migration Guide
SystemSetConfigs -> NodeConfigs<InternedSystemSet>
SystemConfigs -> NodeConfigs<ScheduleSystem>
IntoSystemSetConfigs -> IntoNodeConfigs<InternedSystemSet, M>
IntoSystemConfigs -> IntoNodeConfigs<ScheduleSystem, M>

---------

Co-authored-by: Christian Hughes <9044780+ItsDoot@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-03-12 00:12:30 +00:00
AlephCubed
5f86668bbb
Renamed EventWriter::send methods to write. (#17977)
Fixes #17856.

## Migration Guide
- `EventWriter::send` has been renamed to `EventWriter::write`.
- `EventWriter::send_batch` has been renamed to
`EventWriter::write_batch`.
- `EventWriter::send_default` has been renamed to
`EventWriter::write_default`.

---------

Co-authored-by: François Mockers <mockersf@gmail.com>
2025-02-23 21:18:52 +00:00
Phoqinu
c6147e57f4
Make StateTransitionSteps public (#16612)
# Objective

- Fixes #16594 

## Solution

- `StateTransitionSteps` was made public

## Testing

- _Did you test these changes? If so, how?_
 I am now able to import it and use it.

---

## Showcase

- Users can now write their own state scoped resources

```rust
    fn init_state_scoped_resource<R: Resource + FromWorld>(
        &mut self,
        state: impl States,
    ) -> &mut Self {
        use bevy::state::state::StateTransitionSteps; // this PR in action

        self.add_systems(
            StateTransition,
            (
                clear_state_scoped_resource_impl::<_, R>(state.clone())
                    .in_set(StateTransitionSteps::ExitSchedules), // and here
                init_state_scoped_resource_impl::<_, R>(state)
                    .in_set(StateTransitionSteps::EnterSchedules), // here too
            ),
        );

        self
    }
```
2024-12-03 19:48:00 +00:00
Rob Parrett
30d84519a2
Use en-us locale for typos (#16037)
# Objective

Bevy seems to want to standardize on "American English" spellings. Not
sure if this is laid out anywhere in writing, but see also #15947.

While perusing the docs for `typos`, I noticed that it has a `locale`
config option and tried it out.

## Solution

Switch to `en-us` locale in the `typos` config and run `typos -w`

## Migration Guide

The following methods or fields have been renamed from `*dependants*` to
`*dependents*`.

- `ProcessorAssetInfo::dependants`
- `ProcessorAssetInfos::add_dependant`
- `ProcessorAssetInfos::non_existent_dependants`
- `AssetInfo::dependants_waiting_on_load`
- `AssetInfo::dependants_waiting_on_recursive_dep_load`
- `AssetInfos::loader_dependants`
- `AssetInfos::remove_dependants_and_labels`
2024-10-20 18:55:17 +00:00
Christian Hughes
b4071ca370
Add World::get_resource_or_init as an alternative to World::get_resource_or_insert_with (#15758)
# Objective

If a `Resource` implements `FromWorld` or `Default`, it's nicer to be
able to write:

```rust
let foo = world.get_resource_or_init::<Foo>();
```

Rather than:

```rust
let foo = world.get_resource_or_insert_with(Foo::default);
```

The latter is also not possible if a type implements `FromWorld` only,
and not `Default`.

## Solution

Added:

```rust
impl World {
    pub fn get_resource_or_init<R: Resource + FromWorld>(&mut self) -> Mut<'_, R>;
}
```

Turns out all current in-engine uses of `get_resource_or_insert_with`
are exactly the above, so they've also been replaced.

## Testing

- Added a doc-test.
- Also added a doc-test for `World::get_resource_or_insert_with`.
2024-10-09 20:56:26 +00:00
Zachary Harrold
d70595b667
Add core and alloc over std Lints (#15281)
# Objective

- Fixes #6370
- Closes #6581

## Solution

- Added the following lints to the workspace:
  - `std_instead_of_core`
  - `std_instead_of_alloc`
  - `alloc_instead_of_core`
- Used `cargo +nightly fmt` with [item level use
formatting](https://rust-lang.github.io/rustfmt/?version=v1.6.0&search=#Item%5C%3A)
to split all `use` statements into single items.
- Used `cargo clippy --workspace --all-targets --all-features --fix
--allow-dirty` to _attempt_ to resolve the new linting issues, and
intervened where the lint was unable to resolve the issue automatically
(usually due to needing an `extern crate alloc;` statement in a crate
root).
- Manually removed certain uses of `std` where negative feature gating
prevented `--all-features` from finding the offending uses.
- Used `cargo +nightly fmt` with [crate level use
formatting](https://rust-lang.github.io/rustfmt/?version=v1.6.0&search=#Crate%5C%3A)
to re-merge all `use` statements matching Bevy's previous styling.
- Manually fixed cases where the `fmt` tool could not re-merge `use`
statements due to conditional compilation attributes.

## Testing

- Ran CI locally

## Migration Guide

The MSRV is now 1.81. Please update to this version or higher.

## Notes

- This is a _massive_ change to try and push through, which is why I've
outlined the semi-automatic steps I used to create this PR, in case this
fails and someone else tries again in the future.
- Making this change has no impact on user code, but does mean Bevy
contributors will be warned to use `core` and `alloc` instead of `std`
where possible.
- This lint is a critical first step towards investigating `no_std`
options for Bevy.

---------

Co-authored-by: François Mockers <francois.mockers@vleue.com>
2024-09-27 00:59:59 +00:00
MiniaczQ
bc72cedfe3
Make initial StateTransition run before PreStartup (#14208)
# Objective

- Fixes #14206 

## Solution

- Run initial `StateTransition` as a startup schedule before
`PreStartup`, instead of running it inside `Startup` as an exclusive
system.

Related discord discussion:

https://discord.com/channels/691052431525675048/692572690833473578/1259543775668207678

## Testing

Reproduction now works correctly:

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

#[derive(Debug, Clone, Copy, Default, Eq, PartialEq, Hash, States)]
enum AppState {
    #[default]
    Menu,
    InGame,
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .init_state::<AppState>()
        .add_systems(Startup, setup)
        .add_systems(OnEnter(AppState::Menu), enter_menu_state)
        .run();
}

fn setup(mut next_state: ResMut<NextState<AppState>>) {
    next_state.set(AppState::Menu);
}

fn enter_menu_state() {
    println!("Entered menu state");
}
```


![image](https://github.com/bevyengine/bevy/assets/13040204/96d7a533-c439-4c0b-8f15-49f620903ce1)


---

## Changelog

- Initial `StateTransition` runs before `PreStartup` instead of inside
`Startup`.
2024-07-15 15:08:54 +00:00
Giacomo Stevanato
d7080369a7
Fix intra-doc links and make CI test them (#14076)
# Objective

- Bevy currently has lot of invalid intra-doc links, let's fix them!
- Also make CI test them, to avoid future regressions.
- Helps with #1983 (but doesn't fix it, as there could still be explicit
links to docs.rs that are broken)

## Solution

- Make `cargo r -p ci -- doc-check` check fail on warnings (could also
be changed to just some specific lints)
- Manually fix all the warnings (note that in some cases it was unclear
to me what the fix should have been, I'll try to highlight them in a
self-review)
2024-07-11 13:08:31 +00:00
Lee-Orr
7ec301c48d
fix docs around StateTransition and remove references to `apply_sta… (#13772)
The documentation for the `State` resource still referenced the use of
`apply_state_transition` to manually force a state transition to occur,
and the question around how to force transitions had come up a few times
on discord.

This is a docs-only change, that does the following:
- Properly references `StateTransition` in the `MainSchedule` docs
- replace the explanations for applying `NextState` with ones that
explain the `StateTransition` schedule, and mentions the possibility of
calling it manually
- Add an example of calling `StateTransition` manually in the docs for
the state transition schedule itself.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2024-06-10 13:23:14 +00:00
MiniaczQ
6d0b7504a2
Add more granular system sets for state transition schedule ordering (#13763)
# Objective

Fixes #13711 

## Solution

Introduce smaller, generic system sets for each schedule variant, which
are ordered against other generic variants:
- `ExitSchedules<S>` - For `OnExit` schedules, runs from leaf states to
root states.
- `TransitionSchedules<S>` - For `OnTransition` schedules, runs in
arbitrary order.
- `EnterSchedules<S>` - For `OnEnter` schedules, runs from root states
to leaf states.

Also unified `ApplyStateTransition<S>` schedule which works in basically
the same way, just for internals.

## Testing

- One test that tests schedule execution order

---------

Co-authored-by: Lee-Orr <lee-orr@users.noreply.github.com>
2024-06-10 13:13:58 +00:00
MiniaczQ
49338245ea
Generalize StateTransitionEvent<S> to allow identity transitions (#13579)
# Objective

This PR addresses one of the issues from [discord state
discussion](https://discord.com/channels/691052431525675048/1237949214017716356).
Same-state transitions can be desirable, so there should exist a hook
for them.

Fixes https://github.com/bevyengine/bevy/issues/9130.

## Solution

- Allow `StateTransitionEvent<S>` to contain identity transitions.
- Ignore identity transitions at schedule running level (`OnExit`,
`OnTransition`, `OnEnter`).
- Propagate identity transitions through `SubStates` and
`ComputedStates`.
- Add example about registering custom transition schedules.

## Changelog

- `StateTransitionEvent<S>` can be emitted with same `exited` and
`entered` state.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2024-06-04 14:23:24 +00:00
MiniaczQ
07aa9e5641
Combine transition systems of Substates (#13626)
# Objective

Prerequisite to #13579.
Combine separate `Substates` transition systems to centralize transition
logic and exert more control over it.

## Solution

Originally the transition happened in 2 stages:
- `apply_state_transition` in `ManualTransitions` handled `NextState`,
- closure system in `DependentTransitions` handled parent-related
changes, insertion and deletion of the substate.

Now:
- Both transitions are processed in a single closure system during
`DependentTransitions`.
- Since `Substates` no longer use `ManualTransitions`, it's been renamed
to `RootTransitions`. Only root states use it.
- When `Substates` state comes into existence, it will try to initialize
from `NextState` and fallback to `should_exist` result.
- Remove `apply_state_transition` from public API.

Consequentially, removed the possibility of multiple
`StateTransitionEvent`s when both transition systems fire in a single
frame.

## Changelog

- Renamed `ManualTransitions` to `RootTransitions`.
- `Substates` will initialize their value with `NextState` if available
and fallback to `should_exist` result.

## Migration Guide

- `apply_state_transition` is no longer publicly available, run the
`StateTransition` schedule instead.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2024-06-02 13:36:44 +00:00
MiniaczQ
5cb4808026
Simplify state transitions (#13616)
# Objective

Prerequisite to #13579.
Make state transition schedule running simpler.

## Solution

- Remove `should_run_transition` which read the latest event and
fake-fire an event for the startup transitions (e.g. startup
`OnEnter()`).
- Account for startup event, by actually emitting an event when adding
states to `App`.
- Replace `should_run_transition` with `last_transition`, which is a
light wrapper over `EventReader::read().last()`.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2024-06-01 21:00:38 +00:00
MiniaczQ
912f77b2fe
Unify transition names to exited and entered (#13594)
# Objective

Unifies the naming convention between `StateTransitionEvent<S>` and
transition schedules.

## Migration Guide

- `StateTransitionEvent<S>` and `OnTransition<S>` schedule had their
fields renamed to `exited` and `entered` to match schedules.
2024-05-31 15:20:01 +00:00
Lee-Orr
42ba9dfaea
Separate state crate (#13216)
# Objective

Extracts the state mechanisms into a new crate called "bevy_state".

This comes with a few goals:

- state wasn't really an inherent machinery of the ecs system, and so
keeping it within bevy_ecs felt forced
- by mixing it in with bevy_ecs, the maintainability of our more robust
state system was significantly compromised

moving state into a new crate makes it easier to encapsulate as it's own
feature, and easier to read and understand since it's no longer a
single, massive file.

## Solution

move the state-related elements from bevy_ecs to a new crate

## Testing

- Did you test these changes? If so, how? all the automated tests
migrated and passed, ran the pre-existing examples without changes to
validate.

---

## Migration Guide

Since bevy_state is now gated behind the `bevy_state` feature, projects
that use state but don't use the `default-features` will need to add
that feature flag.

Since it is no longer part of bevy_ecs, projects that use bevy_ecs
directly will need to manually pull in `bevy_state`, trigger the
StateTransition schedule, and handle any of the elements that bevy_app
currently sets up.

---------

Co-authored-by: Kristoffer Søholm <k.soeholm@gmail.com>
2024-05-09 18:06:05 +00:00