Spawn now takes a Bundle (bevyengine#6054)

# Objective

Now that we can consolidate Bundles and Components under a single insert (thanks to bevyengine#2975 and bevyengine#6039), almost 100% of world spawns now look like `world.spawn().insert((Some, Tuple, Here))`. Spawning an entity without any components is an extremely uncommon pattern, so it makes sense to give spawn the "first class" ergonomic api. This consolidated api should be made consistent across all spawn apis (such as World and Commands).

## Solution

All `spawn` apis (`World::spawn`, `Commands:;spawn`, `ChildBuilder::spawn`, and `WorldChildBuilder::spawn`) now accept a bundle as input:

```rust
// before:
commands
  .spawn()
  .insert((A, B, C));
world
  .spawn()
  .insert((A, B, C);

// after
commands.spawn((A, B, C));
world.spawn((A, B, C));
```

All existing instances of `spawn_bundle` have been deprecated in favor of the new `spawn` api. A new `spawn_empty` has been added, replacing the old `spawn` api.  

By allowing `world.spawn(some_bundle)` to replace `world.spawn().insert(some_bundle)`, this opened the door to removing the initial entity allocation in the "empty" archetype / table done in `spawn()` (and subsequent move to the actual archetype in `.insert(some_bundle)`).

This improves spawn performance by over 10%:
![image](https://user-images.githubusercontent.com/2694663/191627587-4ab2f949-4ccd-4231-80eb-80dd4d9ad6b9.png)

To take this measurement, I added a new `world_spawn` benchmark.

Unfortunately, optimizing `Commands::spawn` is slightly less trivial, as Commands expose the Entity id of spawned entities prior to actually spawning. Doing the optimization would (naively) require assurances that the `spawn(some_bundle)` command is applied before all other commands involving the entity (which would not necessarily be true, if memory serves). Optimizing `Commands::spawn` this way does feel possible, but it will require careful thought (and maybe some additional checks), which deserves its own PR. For now, it has the same performance characteristics of the current `Commands::spawn_bundle` on main.

**Note that 99% of this PR is simple renames and refactors. The only code that needs careful scrutiny is the new `World::spawn()` impl, which is relatively straightforward, but it has some new unsafe code (which re-uses battle tested BundlerSpawner code path).** 

---

## Changelog

- All `spawn` apis (`World::spawn`, `Commands:;spawn`, `ChildBuilder::spawn`, and `WorldChildBuilder::spawn`) now accept a bundle as input
- All instances of `spawn_bundle` have been deprecated in favor of the new `spawn` api
- World and Commands now have `spawn_empty()`, which is equivalent to the old `spawn()` behavior.  

## Migration Guide

```rust
// Old (0.8):
commands
  .spawn()
  .insert_bundle((A, B, C));
// New (0.9)
commands.spawn((A, B, C));

// Old (0.8):
commands.spawn_bundle((A, B, C));
// New (0.9)
commands.spawn((A, B, C));

// Old (0.8):
let entity = commands.spawn().id();
// New (0.9)
let entity = commands.spawn_empty().id();

// Old (0.8)
let entity = world.spawn().id();
// New (0.9)
let entity = world.spawn_empty();
```

benches/benches/bevy_ecs/components/add_remove_big_sparse_set.rs

@@ -26,8 +26,7 @@ impl Benchmark {
         for _ in 0..10_000 {
             entities.push(
                 world
-                    .spawn()
-                    .insert((
+                    .spawn((
                         A(Mat4::from_scale(Vec3::ONE)),
                         B(Mat4::from_scale(Vec3::ONE)),
                         C(Mat4::from_scale(Vec3::ONE)),

benches/benches/bevy_ecs/components/add_remove_big_table.rs

@@ -25,8 +25,7 @@ impl Benchmark {
         for _ in 0..10_000 {
             entities.push(
                 world
-                    .spawn()
-                    .insert((
+                    .spawn((
                         A(Mat4::from_scale(Vec3::ONE)),
                         B(Mat4::from_scale(Vec3::ONE)),
                         C(Mat4::from_scale(Vec3::ONE)),

benches/benches/bevy_ecs/components/add_remove_sparse_set.rs

@@ -13,7 +13,7 @@ impl Benchmark {
         let mut world = World::default();
         let mut entities = Vec::with_capacity(10_000);
         for _ in 0..10_000 {
-            entities.push(world.spawn().insert(A(0.0)).id());
+            entities.push(world.spawn(A(0.0)).id());
         }
 
         Self(world, entities)

benches/benches/bevy_ecs/components/add_remove_table.rs

@@ -12,7 +12,7 @@ impl Benchmark {
         let mut world = World::default();
         let mut entities = Vec::with_capacity(10_000);
         for _ in 0..10_000 {
-            entities.push(world.spawn().insert(A(0.0)).id());
+            entities.push(world.spawn(A(0.0)).id());
         }
 
         Self(world, entities)

benches/benches/bevy_ecs/components/archetype_updates.rs

@@ -22,7 +22,7 @@ fn setup(system_count: usize) -> (World, SystemStage) {
 /// create `count` entities with distinct archetypes
 fn add_archetypes(world: &mut World, count: u16) {
     for i in 0..count {
-        let mut e = world.spawn();
+        let mut e = world.spawn_empty();
         if i & 1 << 0 != 0 {
             e.insert(A::<0>(1.0));
         }

benches/benches/bevy_ecs/components/insert_simple_unbatched.rs

@@ -23,7 +23,7 @@ impl Benchmark {
     pub fn run(&mut self) {
         let mut world = World::new();
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Position(Vec3::X),
                 Rotation(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_frag.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..20 {
-                $world.spawn().insert(($variants(0.0), Data(1.0)));
+                $world.spawn(($variants(0.0), Data(1.0)));
             }
         )*
     };

benches/benches/bevy_ecs/iteration/iter_frag_foreach.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..20 {
-                $world.spawn().insert(($variants(0.0), Data(1.0)));
+                $world.spawn(($variants(0.0), Data(1.0)));
             }
         )*
     };

benches/benches/bevy_ecs/iteration/iter_frag_foreach_sparse.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..5 {
-                $world.spawn().insert($variants(0.0));
+                $world.spawn($variants(0.0));
             }
         )*
     };
@@ -21,7 +21,7 @@ impl<'w> Benchmark<'w> {
     pub fn new() -> Self {
         let mut world = World::new();
         for _ in 0..5 {
-            world.spawn().insert(Data(1.0));
+            world.spawn(Data(1.0));
         }
 
         create_entities!(world; C00, C01, C02, C03, C04, C05, C06, C07, C08, C09);

benches/benches/bevy_ecs/iteration/iter_frag_foreach_wide.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..20 {
-                $world.spawn().insert((
+                $world.spawn((
                     $variants(0.0),
                     Data::<0>(1.0),
                     Data::<1>(1.0),

benches/benches/bevy_ecs/iteration/iter_frag_foreach_wide_sparse.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..5 {
-                $world.spawn().insert($variants(0.0));
+                $world.spawn($variants(0.0));
             }
         )*
     };
@@ -36,7 +36,7 @@ impl<'w> Benchmark<'w> {
     pub fn new() -> Self {
         let mut world = World::new();
         for _ in 0..5 {
-            world.spawn().insert((
+            world.spawn((
                 Data::<0>(1.0),
                 Data::<1>(1.0),
                 Data::<2>(1.0),

benches/benches/bevy_ecs/iteration/iter_frag_sparse.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..5 {
-                $world.spawn().insert($variants(0.0));
+                $world.spawn($variants(0.0));
             }
         )*
     };
@@ -21,7 +21,7 @@ impl<'w> Benchmark<'w> {
         let mut world = World::new();
 
         for _ in 0..5 {
-            world.spawn().insert(Data(1.0));
+            world.spawn(Data(1.0));
         }
 
         create_entities!(world; C00, C01, C02, C03, C04, C05, C06, C07, C08, C09);

benches/benches/bevy_ecs/iteration/iter_frag_wide.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..20 {
-                $world.spawn().insert((
+                $world.spawn((
                     $variants(0.0),
                     Data::<0>(1.0),
                     Data::<1>(1.0),

benches/benches/bevy_ecs/iteration/iter_frag_wide_sparse.rs

@@ -6,7 +6,7 @@ macro_rules! create_entities {
             #[derive(Component)]
             struct $variants(f32);
             for _ in 0..5 {
-                $world.spawn().insert($variants(0.0));
+                $world.spawn($variants(0.0));
             }
         )*
     };
@@ -36,7 +36,7 @@ impl<'w> Benchmark<'w> {
         let mut world = World::new();
 
         for _ in 0..5 {
-            world.spawn().insert((
+            world.spawn((
                 Data::<0>(1.0),
                 Data::<1>(1.0),
                 Data::<2>(1.0),

benches/benches/bevy_ecs/iteration/iter_simple.rs

@@ -21,7 +21,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Position(Vec3::X),
                 Rotation(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_foreach.rs

@@ -21,7 +21,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Position(Vec3::X),
                 Rotation(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_foreach_sparse_set.rs

@@ -23,7 +23,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Position(Vec3::X),
                 Rotation(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_foreach_wide.rs

@@ -35,7 +35,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Rotation(Vec3::X),
                 Position::<0>(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_foreach_wide_sparse_set.rs

@@ -37,7 +37,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Rotation(Vec3::X),
                 Position::<0>(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_sparse_set.rs

@@ -23,7 +23,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Position(Vec3::X),
                 Rotation(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_system.rs

@@ -21,7 +21,7 @@ impl Benchmark {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Position(Vec3::X),
                 Rotation(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_wide.rs

@@ -35,7 +35,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Rotation(Vec3::X),
                 Position::<0>(Vec3::X),

benches/benches/bevy_ecs/iteration/iter_simple_wide_sparse_set.rs

@@ -37,7 +37,7 @@ impl<'w> Benchmark<'w> {
 
         // TODO: batch this
         for _ in 0..10_000 {
-            world.spawn().insert((
+            world.spawn((
                 Transform(Mat4::from_scale(Vec3::ONE)),
                 Rotation(Vec3::X),
                 Position::<0>(Vec3::X),

benches/benches/bevy_ecs/scheduling/run_criteria.rs

@@ -150,7 +150,7 @@ struct TestBool(pub bool);
 
 pub fn run_criteria_yes_with_query(criterion: &mut Criterion) {
     let mut world = World::new();
-    world.spawn().insert(TestBool(true));
+    world.spawn(TestBool(true));
     let mut group = criterion.benchmark_group("run_criteria/yes_using_query");
     group.warm_up_time(std::time::Duration::from_millis(500));
     group.measurement_time(std::time::Duration::from_secs(3));

benches/benches/bevy_ecs/world/commands.rs

@@ -43,7 +43,7 @@ pub fn spawn_commands(criterion: &mut Criterion) {
             bencher.iter(|| {
                 let mut commands = Commands::new(&mut command_queue, &world);
                 for i in 0..entity_count {
-                    let mut entity = commands.spawn();
+                    let mut entity = commands.spawn_empty();
 
                     if black_box(i % 2 == 0) {
                         entity.insert(A);
@@ -87,7 +87,7 @@ pub fn insert_commands(criterion: &mut Criterion) {
         let mut command_queue = CommandQueue::default();
         let mut entities = Vec::new();
         for _ in 0..entity_count {
-            entities.push(world.spawn().id());
+            entities.push(world.spawn_empty().id());
         }
 
         bencher.iter(|| {
@@ -106,7 +106,7 @@ pub fn insert_commands(criterion: &mut Criterion) {
         let mut command_queue = CommandQueue::default();
         let mut entities = Vec::new();
         for _ in 0..entity_count {
-            entities.push(world.spawn().id());
+            entities.push(world.spawn_empty().id());
         }
 
         bencher.iter(|| {

benches/benches/bevy_ecs/world/mod.rs

@@ -1,9 +1,11 @@
 use criterion::criterion_group;
 
 mod commands;
+mod spawn;
 mod world_get;
 
 use commands::*;
+use spawn::*;
 use world_get::*;
 
 criterion_group!(
@@ -21,6 +23,7 @@ criterion_group!(
     world_query_get,
     world_query_iter,
     world_query_for_each,
+    world_spawn,
     query_get_component_simple,
     query_get_component,
     query_get,

benches/benches/bevy_ecs/world/spawn.rs

@@ -0,0 +1,27 @@
+use bevy_ecs::prelude::*;
+use criterion::Criterion;
+use glam::*;
+
+#[derive(Component)]
+struct A(Mat4);
+#[derive(Component)]
+struct B(Vec4);
+
+pub fn world_spawn(criterion: &mut Criterion) {
+    let mut group = criterion.benchmark_group("spawn_world");
+    group.warm_up_time(std::time::Duration::from_millis(500));
+    group.measurement_time(std::time::Duration::from_secs(4));
+
+    for entity_count in (0..5).map(|i| 10_u32.pow(i)) {
+        group.bench_function(format!("{}_entities", entity_count), |bencher| {
+            let mut world = World::default();
+            bencher.iter(|| {
+                for _ in 0..entity_count {
+                    world.spawn((A(Mat4::default()), B(Vec4::default())));
+                }
+            });
+        });
+    }
+
+    group.finish();
+}

benches/benches/bevy_ecs/world/world_get.rs

@@ -268,7 +268,7 @@ pub fn query_get_component_simple(criterion: &mut Criterion) {
     group.bench_function("unchecked", |bencher| {
         let mut world = World::new();
 
-        let entity = world.spawn().insert(A(0.0)).id();
+        let entity = world.spawn(A(0.0)).id();
         let mut query = world.query::<&mut A>();
 
         bencher.iter(|| {
@@ -281,7 +281,7 @@ pub fn query_get_component_simple(criterion: &mut Criterion) {
     group.bench_function("system", |bencher| {
         let mut world = World::new();
 
-        let entity = world.spawn().insert(A(0.0)).id();
+        let entity = world.spawn(A(0.0)).id();
         fn query_system(In(entity): In<Entity>, mut query: Query<&mut A>) {
             for _ in 0..100_000 {
                 let mut a = query.get_mut(entity).unwrap();

crates/bevy_ecs/README.md

@@ -57,9 +57,8 @@ struct Velocity { x: f32, y: f32 }
 
 let mut world = World::new();
 
-let entity = world.spawn()
-    .insert(Position { x: 0.0, y: 0.0 })
-    .insert(Velocity { x: 1.0, y: 0.0 })
+let entity = world
+    .spawn((Position { x: 0.0, y: 0.0 }, Velocity { x: 1.0, y: 0.0 }))
     .id();
 
 let entity_ref = world.entity(entity);
@@ -141,9 +140,10 @@ fn main() {
     let mut world = World::new();
 
     // Spawn an entity with Position and Velocity components
-    world.spawn()
-        .insert(Position { x: 0.0, y: 0.0 })
-        .insert(Velocity { x: 1.0, y: 0.0 });
+    world.spawn((
+        Position { x: 0.0, y: 0.0 },
+        Velocity { x: 1.0, y: 0.0 },
+    ));
 
     // Create a new Schedule, which defines an execution strategy for Systems
     let mut schedule = Schedule::default();
@@ -276,10 +276,10 @@ struct PlayerBundle {
 let mut world = World::new();
 
 // Spawn a new entity and insert the default PlayerBundle
-world.spawn().insert(PlayerBundle::default());
+world.spawn(PlayerBundle::default());
 
 // Bundles play well with Rust's struct update syntax
-world.spawn().insert(PlayerBundle {
+world.spawn(PlayerBundle {
     position: Position { x: 1.0, y: 1.0 },
     ..Default::default()
 });

crates/bevy_ecs/examples/change_detection.rs

@@ -65,7 +65,7 @@ enum SimulationSystem {
 // If an entity gets spawned, we increase the counter in the EntityCounter resource
 fn spawn_entities(mut commands: Commands, mut entity_counter: ResMut<EntityCounter>) {
     if rand::thread_rng().gen_bool(0.6) {
-        let entity_id = commands.spawn_bundle(Age::default()).id();
+        let entity_id = commands.spawn(Age::default()).id();
         println!("    spawning {:?}", entity_id);
         entity_counter.value += 1;
     }