Replace bevy_a11y::Focus with InputFocus (#16863)

# Objective

Bevy now has first-class input focus handling! We should use this for
accessibility purpose via accesskit too.

## Solution

- Removed bevy_a11y::Focus.
- Replaced all usages of Focus with InputFocus
- Changed the dependency tree so bevy_a11y relies on bevy_input_focus
- Moved initialization of the focus (starts with the primary window)
from bevy_window to bevy_input_focus to avoid circular dependencies (and
it's cleaner)

## Testing

TODO

## Migration Guide

`bevy_a11y::Focus` has been replaced with `bevy_input_focus::Focus`.

crates/bevy_a11y/Cargo.toml

@@ -14,6 +14,7 @@ bevy_app = { path = "../bevy_app", version = "0.15.0-dev" }
 bevy_derive = { path = "../bevy_derive", version = "0.15.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev" }
+bevy_input_focus = { path = "../bevy_input_focus", version = "0.15.0-dev" }
 
 accesskit = "0.17"
 

crates/bevy_a11y/src/lib.rs

@@ -22,11 +22,10 @@ use accesskit::Node;
 use bevy_app::Plugin;
 use bevy_derive::{Deref, DerefMut};
 use bevy_ecs::{
-    prelude::{Component, Entity, Event, ReflectResource},
+    prelude::{Component, Event},
     schedule::SystemSet,
     system::Resource,
 };
-use bevy_reflect::{std_traits::ReflectDefault, Reflect};
 
 /// Wrapper struct for [`accesskit::ActionRequest`]. Required to allow it to be used as an `Event`.
 #[derive(Event, Deref, DerefMut)]
@@ -97,11 +96,6 @@ impl From<Node> for AccessibilityNode {
     }
 }
 
-/// Resource representing which entity has keyboard focus, if any.
-#[derive(Resource, Default, Deref, DerefMut, Reflect)]
-#[reflect(Resource, Default)]
-pub struct Focus(pub Option<Entity>);
-
 /// Set enum for the systems relating to accessibility
 #[derive(Debug, Hash, PartialEq, Eq, Clone, SystemSet)]
 pub enum AccessibilitySystem {
@@ -115,11 +109,8 @@ pub struct AccessibilityPlugin;
 
 impl Plugin for AccessibilityPlugin {
     fn build(&self, app: &mut bevy_app::App) {
-        app.register_type::<Focus>();
-
         app.init_resource::<AccessibilityRequested>()
             .init_resource::<ManageAccessibilityUpdates>()
-            .init_resource::<Focus>()
             .allow_ambiguous_component::<AccessibilityNode>();
     }
 }

crates/bevy_input_focus/src/lib.rs

@@ -18,13 +18,13 @@
 
 pub mod tab_navigation;
 
-use bevy_app::{App, Plugin, PreUpdate};
+use bevy_app::{App, Plugin, PreUpdate, Startup};
 use bevy_ecs::{
     component::Component,
     entity::Entity,
     event::{Event, EventReader},
     query::{QueryData, With},
-    system::{Commands, Query, Res, Resource, SystemParam},
+    system::{Commands, Query, Res, ResMut, Resource, Single, SystemParam},
     traversal::Traversal,
     world::{Command, DeferredWorld, World},
 };
@@ -149,12 +149,21 @@ pub struct InputDispatchPlugin;
 
 impl Plugin for InputDispatchPlugin {
     fn build(&self, app: &mut App) {
-        app.insert_resource(InputFocus(None))
+        app.add_systems(Startup, set_initial_focus)
+            .insert_resource(InputFocus(None))
             .insert_resource(InputFocusVisible(false))
             .add_systems(PreUpdate, dispatch_keyboard_input);
     }
 }
 
+/// Sets the initial focus to the primary window, if any.
+pub fn set_initial_focus(
+    mut input_focus: ResMut<InputFocus>,
+    window: Single<Entity, With<PrimaryWindow>>,
+) {
+    input_focus.0 = Some(*window);
+}
+
 /// System which dispatches keyboard input events to the focused entity, or to the primary window
 /// if no entity has focus.
 fn dispatch_keyboard_input(
@@ -377,6 +386,9 @@ mod tests {
         };
         app.world_mut().spawn((window, PrimaryWindow));
 
+        // Run the world for a single frame to set up the initial focus
+        app.update();
+
         let entity_a = app
             .world_mut()
             .spawn((GatherKeyboardEvents::default(), SetFocusOnAdd))

crates/bevy_window/Cargo.toml

@@ -13,7 +13,6 @@ serialize = ["serde", "smol_str/serde", "bevy_ecs/serialize"]
 
 [dependencies]
 # bevy
-bevy_a11y = { path = "../bevy_a11y", version = "0.15.0-dev" }
 bevy_app = { path = "../bevy_app", version = "0.15.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev" }
 bevy_input = { path = "../bevy_input", version = "0.15.0-dev" }

crates/bevy_window/src/lib.rs

@@ -16,8 +16,6 @@ extern crate alloc;
 use alloc::sync::Arc;
 use std::sync::Mutex;
 
-use bevy_a11y::Focus;
-
 mod event;
 mod monitor;
 mod raw_handle;
@@ -118,17 +116,10 @@ impl Plugin for WindowPlugin {
             .add_event::<AppLifecycle>();
 
         if let Some(primary_window) = &self.primary_window {
-            let initial_focus = app
-                .world_mut()
-                .spawn(primary_window.clone())
-                .insert((
-                    PrimaryWindow,
-                    RawHandleWrapperHolder(Arc::new(Mutex::new(None))),
-                ))
-                .id();
-            if let Some(mut focus) = app.world_mut().get_resource_mut::<Focus>() {
-                **focus = Some(initial_focus);
-            }
+            app.world_mut().spawn(primary_window.clone()).insert((
+                PrimaryWindow,
+                RawHandleWrapperHolder(Arc::new(Mutex::new(None))),
+            ));
         }
 
         match self.exit_condition {

crates/bevy_winit/Cargo.toml

@@ -29,6 +29,7 @@ bevy_derive = { path = "../bevy_derive", version = "0.15.0-dev" }
 bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev" }
 bevy_hierarchy = { path = "../bevy_hierarchy", version = "0.15.0-dev" }
 bevy_input = { path = "../bevy_input", version = "0.15.0-dev" }
+bevy_input_focus = { path = "../bevy_input_focus", version = "0.15.0-dev" }
 bevy_log = { path = "../bevy_log", version = "0.15.0-dev" }
 bevy_math = { path = "../bevy_math", version = "0.15.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev" }

crates/bevy_winit/src/accessibility.rs

@@ -1,6 +1,7 @@
 //! Helpers for mapping window entities to accessibility types
 
 use alloc::{collections::VecDeque, sync::Arc};
+use bevy_input_focus::InputFocus;
 use std::sync::Mutex;
 
 use accesskit::{
@@ -10,13 +11,14 @@ use accesskit::{
 use accesskit_winit::Adapter;
 use bevy_a11y::{
     AccessibilityNode, AccessibilityRequested, AccessibilitySystem,
-    ActionRequest as ActionRequestWrapper, Focus, ManageAccessibilityUpdates,
+    ActionRequest as ActionRequestWrapper, ManageAccessibilityUpdates,
 };
 use bevy_app::{App, Plugin, PostUpdate};
 use bevy_derive::{Deref, DerefMut};
 use bevy_ecs::{
+    change_detection::DetectChanges,
     entity::EntityHashMap,
-    prelude::{DetectChanges, Entity, EventReader, EventWriter},
+    prelude::{Entity, EventReader, EventWriter},
     query::With,
     schedule::IntoSystemConfigs,
     system::{NonSendMut, Query, Res, ResMut, Resource},
@@ -179,7 +181,7 @@ fn should_update_accessibility_nodes(
 
 fn update_accessibility_nodes(
     mut adapters: NonSendMut<AccessKitAdapters>,
-    focus: Res<Focus>,
+    focus: Res<InputFocus>,
     primary_window: Query<(Entity, &Window), With<PrimaryWindow>>,
     nodes: Query<(
         Entity,
@@ -218,7 +220,7 @@ fn update_adapter(
     node_entities: Query<Entity, With<AccessibilityNode>>,
     primary_window: &Window,
     primary_window_id: Entity,
-    focus: Res<Focus>,
+    focus: Res<InputFocus>,
 ) -> TreeUpdate {
     let mut to_update = vec![];
     let mut window_children = vec![];
@@ -241,7 +243,7 @@ fn update_adapter(
     TreeUpdate {
         nodes: to_update,
         tree: None,
-        focus: NodeId(focus.unwrap_or(primary_window_id).to_bits()),
+        focus: NodeId(focus.0.unwrap_or(primary_window_id).to_bits()),
     }
 }