Adding WorldQuery for WithBundle (#2024)

In response to #2023, here is a draft for a PR. 

Fixes #2023

I've added an example to show how to use `WithBundle`, and also to test it out. 

Right now there is a bug: If a bundle and a query are "the same", then it doesn't filter out
what it needs to filter out. 

Example: 

```
Print component initated from bundle.
[examples/ecs/query_bundle.rs:57] x = Dummy( <========= This should not get printed
    111,
)
[examples/ecs/query_bundle.rs:57] x = Dummy(
    222,
)
Show all components
[examples/ecs/query_bundle.rs:50] x = Dummy(
    111,
)
[examples/ecs/query_bundle.rs:50] x = Dummy(
    222,
)
```

However, it behaves the right way, if I add one more component to the bundle,
so the query and the bundle doesn't look the same:

```
Print component initated from bundle.
[examples/ecs/query_bundle.rs:57] x = Dummy(
    222,
)
Show all components
[examples/ecs/query_bundle.rs:50] x = Dummy(
    111,
)
[examples/ecs/query_bundle.rs:50] x = Dummy(
    222,
)
```

I hope this helps. I'm definitely up for tinkering with this, and adding anything that I'm asked to add
or change. 





Co-authored-by: Carter Anderson <mcanders1@gmail.com>

Cargo.toml

@@ -302,6 +302,10 @@ path = "examples/ecs/system_sets.rs"
 name = "timers"
 path = "examples/ecs/timers.rs"
 
+[[example]]
+name = "query_bundle"
+path = "examples/ecs/query_bundle.rs"
+
 # Games
 [[example]]
 name = "alien_cake_addict"

crates/bevy_ecs/src/bundle.rs

@@ -12,7 +12,7 @@ use std::{any::TypeId, collections::HashMap};
 /// An ordered collection of components, commonly used for spawning entities, and adding and
 /// removing components in bulk.
 ///
-/// You cannot query for a bundle, only individual components within it.
+/// In order to query for components in a bundle use [crate::query::WithBundle].
 ///
 /// Typically, you will simply use `#[derive(Bundle)]` when creating your own `Bundle`.
 /// The `Bundle` trait is automatically implemented for tuples of components:

crates/bevy_ecs/src/query/filter.rs

@@ -295,6 +295,11 @@ impl<'a, T: Component> Fetch<'a> for WithoutFetch<T> {
 
 pub struct WithBundle<T: Bundle>(PhantomData<T>);
 
+impl<T: Bundle> WorldQuery for WithBundle<T> {
+    type Fetch = WithBundleFetch<T>;
+    type State = WithBundleState<T>;
+}
+
 pub struct WithBundleFetch<T: Bundle> {
     is_dense: bool,
     marker: PhantomData<T>,

examples/README.md

@@ -32,6 +32,8 @@ git checkout v0.4.0
 
 ## Table of Contents
 
+- [Examples](#examples)
+  - [Table of Contents](#table-of-contents)
 - [The Bare Minimum](#the-bare-minimum)
   - [Hello, World!](#hello-world)
 - [Cross-Platform Examples](#cross-platform-examples)
@@ -53,8 +55,15 @@ git checkout v0.4.0
   - [Window](#window)
 - [Platform-Specific Examples](#platform-specific-examples)
   - [Android](#android)
+    - [Setup](#setup)
+    - [Build & Run](#build--run)
+    - [Old phones](#old-phones)
   - [iOS](#ios)
+    - [Setup](#setup-1)
+    - [Build & Run](#build--run-1)
   - [WASM](#wasm)
+    - [Setup](#setup-2)
+    - [Build & Run](#build--run-2)
 
 # The Bare Minimum
 
@@ -145,6 +154,7 @@ Example | File | Description
 `fixed_timestep` | [`ecs/fixed_timestep.rs`](./ecs/fixed_timestep.rs) | Shows how to create systems that run every fixed timestep, rather than every tick
 `hierarchy` | [`ecs/hierarchy.rs`](./ecs/hierarchy.rs) | Creates a hierarchy of parents and children entities
 `parallel_query` | [`ecs/parallel_query.rs`](./ecs/parallel_query.rs) | Illustrates parallel queries with `ParallelIterator`
+`query_bundle` | [`ecs/query_bundle.rs`](./ecs/query_bundle.rs) | Shows how to query entities that contain components in a `Bundle`
 `removal_detection` | [`ecs/removal_detection.rs`](./ecs/removal_detection.rs) | Query for entities that had a specific component removed in a previous stage during the current frame.
 `startup_system` | [`ecs/startup_system.rs`](./ecs/startup_system.rs) | Demonstrates a startup system (one that runs once when the app starts up)
 `state` | [`ecs/state.rs`](./ecs/state.rs) | Illustrates how to use States to control transitioning from a Menu state to an InGame state

examples/ecs/query_bundle.rs

@@ -0,0 +1,50 @@
+use bevy::{log::LogPlugin, prelude::*};
+
+fn main() {
+    App::build()
+        .add_plugin(LogPlugin)
+        .add_startup_system(setup.system())
+        .add_system(log_names.system().label(LogNamesSystem))
+        .add_system(log_person_bundles.system().after(LogNamesSystem))
+        .run();
+}
+
+#[derive(Debug, Hash, PartialEq, Eq, Clone, SystemLabel)]
+struct LogNamesSystem;
+
+#[derive(Debug)]
+struct Name(String);
+
+#[derive(Debug)]
+struct Age(usize);
+
+#[derive(Debug, Bundle)]
+struct PersonBundle {
+    name: Name,
+    age: Age,
+}
+
+/// Sets up two entities, one with a [Name] component as part of a bundle,
+/// and one entity with [Name] only.
+fn setup(mut commands: Commands) {
+    commands.spawn().insert(Name("Steve".to_string()));
+    commands.spawn().insert_bundle(PersonBundle {
+        name: Name("Bob".to_string()),
+        age: Age(40),
+    });
+}
+
+fn log_names(query: Query<&Name>) {
+    info!("Log all entities with `Name` component");
+    // this will necessarily have to print both components.
+    for name in query.iter() {
+        info!("{:?}", name);
+    }
+}
+fn log_person_bundles(query: Query<&Name, WithBundle<PersonBundle>>) {
+    info!("Log `Name` components from entities that have all components in `PersonBundle`.");
+    // this should only print `Name("Bob")`.
+    for name in query.iter() {
+        info!("{:?}", name);
+    }
+}