Start 0.5 -> 0.6 Migration guide (#185)

Author: MinerSebas

content/learn/book/migration-guides/0.5-0.6/_index.md

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++++
+title = "0.5 to 0.6"
+weight = 1
+sort_by = "weight"
+template = "book-section.html"
+page_template = "book-section.html"
+[extra]
+long_title = "Migration Guide: 0.5 to 0.6"
++++
+
+### "AppBuilder" was merged into "App"
+
+All functions of {{rust_type(type="struct" crate="bevy_app" mod="" version="0.5.0" name="AppBuilder" no_mod=true)}} were merged into {{rust_type(type="struct" crate="bevy_app" mod="" version="0.6.0" name="App" no_mod=true)}}.
+
+In practice this means that you start constructing an {{rust_type(type="struct" crate="bevy_app" mod="" version="0.6.0" name="App" no_mod=true)}} by calling {{rust_type(type="struct" crate="bevy_app" mod="" version="0.6.0" name="App" no_mod=true method="new")}} instead of {{rust_type(type="struct" crate="bevy_app" mod="" version="0.5.0" name="App" no_mod=true method="build")}} and {{rust_type(type="trait" crate="bevy_app" mod="" version="0.5.0" name="Plugin" no_mod=true method="build")}} takes a {{rust_type(type="struct" crate="bevy_app" mod="" version="0.6.0" name="App" no_mod=true)}} instead of a {{rust_type(type="struct" crate="bevy_app" mod="" version="0.5.0" name="AppBuilder" no_mod=true)}}
+
+```rs
+// 0.5
+fn main() {
+    App::build()
+        .add_plugin(SomePlugin)
+        .run();
+}
+
+impl Plugin for SomePlugin {
+    fn build(&self, app: &mut AppBuilder) {
+
+    }
+}
+
+// 0.6
+fn main() {
+    App::new()
+        .add_plugin(SomePlugin)
+        .run();
+}
+
+impl Plugin for SomePlugin {
+    fn build(&self, app: &mut App) {
+
+    }
+}
+```
+
+### The "Component" trait now needs to be derived
+
+Bevy no longer has a blanket implementation for the {{rust_type(type="trait" crate="bevy_ecs" mod="component" version="0.6.0" name="Component" no_mod=true)}} trait.
+Instead you need to derive (or manualy implement) the trait for every Type that needs it.
+
+```rust
+// 0.5
+struct MyComponent;
+
+// 0.6
+#[derive(Component)]
+struct MyComponent;
+```
+
+In order to use foreign types as components, wrap them using the newtype pattern.
+
+```rust
+#[derive(Component)]
+struct Cooldown(std::time::Duration);
+```
+
+### Setting the Component Storage is now done in "Component" Trait
+
+The change to deriving {{rust_type(type="trait" crate="bevy_ecs" mod="component" version="0.6.0" name="Component" no_mod=true)}}, enabled setting the Component Storage at compiletime instead of runtime.
+
+```rust
+// 0.5
+appbuilder
+    .world
+    .register_component(ComponentDescriptor::new::<MyComponent>(
+        StorageType::SparseSet,
+    ))
+    .unwrap();
+
+// 0.6
+#[derive(Component)]
+#[component(storage = "SparseSet")]
+struct MyComponent;
+```
+
+### Calling ".system()" on a system is now optional
+
+When adding a system to Bevy it is no longer necessary to call `.system()` beforehand.
+
+```rust
+// 0.5
+fn main() {
+    App::build()
+        .add_system(first_system.system())
+        .add_system(second_system.system())
+        .run();
+}
+
+// 0.6
+fn main() {
+    App::new()
+        .add_system(first_system)
+        .add_system(second_system.system())
+        .run();
+}
+```
+
+System configuration Functions like `.label()` or `.config()` can now also be directly called on a system.
+
+```rust
+// 0.5
+fn main() {
+    App::build()
+        .add_system(first_system.system().label("FirstSystem"))
+        .add_system(second_system.system().after("FirstSystem"))
+        .run();
+}
+
+// 0.6
+fn main() {
+    App::new()
+        .add_system(first_system.label("FirstSystem"))
+        .add_system(second_system.after("FirstSystem"))
+        .run();
+}
+```
+
+### ".single()" and ".single_mut()" are now infallible
+
+The functions {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.6.0" name="Query" no_mod=true method="single")}} and {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.6.0" name="Query" no_mod=true method="single_mut")}} no longer return a {{rust_type(type="enum", crate="std" mod="result", name="Result", no_mod=true)}} and Panic instead, if not exactly one Entity was found.
+
+If you need the old behavior you can use the fallible {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.6.0" name="Query" no_mod=true method="get_single")}} and {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.6.0" name="Query" no_mod=true method="get_single_mut")}} instead.
+
+```rs
+// 0.5
+fn player_system(query: Query<&Transform, With<Player>>) {
+    let player_position = query.single().unwrap();
+    // do something with player_position
+}
+
+// 0.6
+fn player_system_infallible(query: Query<&Transform, With<Player>>) {
+    let player_position = query.single();
+    // do something with player_position
+}
+
+fn player_system_fallible(query: Query<&Transform, With<Player>>) {
+    let player_position = query.get_single().unwrap();
+    // do something with player_position
+}
+```
+
+### "Light" and "LightBundle" are now "PointLight" and "PointLightBundle"
+
+```rust
+// 0.5
+commands.spawn_bundle(LightBundle {
+    light: Light {
+        color: Color::rgb(1.0, 1.0, 1.0),
+        depth: 0.1..50.0,
+        fov: f32::to_radians(60.0),
+        intensity: 200.0,
+        range: 20.0,
+    },
+    ..Default::default()
+});
+
+// 0.6
+commands.spawn_bundle(PointLightBundle {
+    light: PointLight {
+        color: Color::rgb(1.0, 1.0, 1.0),
+        intensity: 200.0,
+        range: 20.0,
+    },
+    ..Default::default()
+});
+```
+
+The {{rust_type(type="struct" crate="bevy_pbr" mod="" version="0.5.0" name="Light" no_mod=true)}} and {{rust_type(type="struct" crate="bevy_pbr" mod="" version="0.5.0" name="LightBundle" no_mod=true)}} were renamed to {{rust_type(type="struct" crate="bevy_pbr" mod="" version="0.6.0" name="PointLight" no_mod=true)}} and {{rust_type(type="struct" crate="bevy_pbr" mod="" version="0.6.0" name="PointLightBundle" no_mod=true)}} to more clearly communicate the behavior of the Light Source.
+At the same time the `fov` and `depth` fields were removed from the {{rust_type(type="struct" crate="bevy_pbr" mod="" version="0.6.0" name="PointLight" no_mod=true)}} as they were unused.
+
+<!-- TODO: Remove this comment if https://github.com/bevyengine/bevy/pull/2367 is merged.
+
+In addition the {{rust_type(type="struct" crate="bevy_pbr" mod="" version="0.6.0" name="DirectionalLight" no_mod=true)}} and {{rust_type(type="struct" crate="bevy_pbr" mod="" version="0.6.0" name="DirectionalLightBundle" no_mod=true)}} were introduced with `0.6`.
+
+-->
+
+### System Param Lifetime Split
+
+The Lifetime of {{rust_type(type="trait" crate="bevy_ecs" mod="system" version="0.5.0" name="SystemParam" no_mod=true)}} was split in two separate Lifetimes.
+
+```rust
+// 0.5
+type SystemParamAlias<'a> = (Res<'a, AssetServer>, Query<'a, &'static Transform>, Local<'a, i32>);
+
+#[derive(SystemParam)]
+struct SystemParamDerive<'a> {
+    res: Res<'a, AssetServer>,
+    query: Query<'a, &Transform>,
+    local: Local<'a, i32>,
+}
+
+// 0.6
+type SystemParamAlias<'w, 's> = (Res<'w, AssetServer>, Query<'w, 's, &'static Transform>, Local<'s, i32>);
+
+#[derive(SystemParam)]
+struct SystemParamDerive<'w, 's> {
+    res: Res<'w, AssetServer>,
+    query: Query<'w, 's, &'static Transform>,
+    local: Local<'s, i32>,
+}
+```
+
+### QuerySet declare "QueryState" instead of "Query"
+<!-- Adapt for ParamSet instead, if https://github.com/bevyengine/bevy/pull/2765 is merged -->
+
+Due to the [System Param Lifetime Split](#system-param-lifetime-split), {{rust_type(type="struct" crate="bevy_ecs" mod="system" name="QuerySet" version="0.6.0" no_mod=true plural=true)}} now need to specify their Queries with {{rust_type(type="struct" crate="bevy_ecs" mod="query" version="0.6.0" name="QuerySet" no_mod=true)}} instead of {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.6.0" name="Query" no_mod=true)}}.
+
+```rust
+// 0.5
+fn query_set(mut queries: QuerySet<(Query<&mut Transform>, Query<&Transform>)>) {
+
+}
+
+// 0.6
+fn query_set(mut queries: QuerySet<(QueryState<&mut Transform>, QueryState<&Transform>)>) {
+
+}
+```
+
+### "Input\<T\>.update()" is renamed to "Input\<T\>.clear()"
+
+The {{rust_type(type="struct" crate="bevy_input" mod="" version="0.5.0" name="Input" no_mod=true method="update")}} function was renamed to {{rust_type(type="struct" crate="bevy_input" mod="" version="0.6.0" name="Input" no_mod=true method="clear")}}.
+
+### "SystemState" is now "SystemMeta"
+
+The {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.5.0" name="SystemState" no_mod=true)}} struct, which stores the metadata of a System, was renamed to {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.6.0" name="SystemMeta" no_mod=true)}}.
+
+This was done to accommodate the new {{rust_type(type="struct" crate="bevy_ecs" mod="system" version="0.6.0" name="SystemState" no_mod=true)}} which allows easier cached access to {{rust_type(type="trait" crate="bevy_ecs" mod="system" version="0.6.0" name="SystemParam" no_mod=true plural=true)}} outside of a regular System.
+<!-- TODO: Link to entry for SystemState in the release blog post. -->