Add no_std Support to bevy_a11y (#17505)

# Objective

- Contributes to #15460

## Solution

- Add `std` feature gate
- Fixed partially used serialisation and reflection features.

## Testing

- CI

crates/bevy_a11y/Cargo.toml

@@ -8,15 +8,73 @@ repository = "https://github.com/bevyengine/bevy"
 license = "MIT OR Apache-2.0"
 keywords = ["bevy", "accessibility", "a11y"]
 
+[features]
+default = ["std", "bevy_reflect", "bevy_ecs/async_executor"]
+
+# Functionality
+
+## Adds runtime reflection support using `bevy_reflect`.
+bevy_reflect = [
+  "dep:bevy_reflect",
+  "bevy_app/bevy_reflect",
+  "bevy_ecs/bevy_reflect",
+  "bevy_input_focus/bevy_reflect",
+]
+
+## Adds serialization support through `serde`.
+serialize = [
+  "dep:serde",
+  "bevy_ecs/serialize",
+  "bevy_input_focus/serialize",
+  "accesskit/serde",
+]
+
+# Platform Compatibility
+
+## Allows access to the `std` crate. Enabling this feature will prevent compilation
+## on `no_std` targets, but provides access to certain additional features on
+## supported platforms.
+std = [
+  "bevy_app/std",
+  "bevy_ecs/std",
+  "bevy_reflect/std",
+  "bevy_input_focus/std",
+]
+
+## `critical-section` provides the building blocks for synchronization primitives
+## on all platforms, including `no_std`.
+critical-section = [
+  "bevy_app/critical-section",
+  "bevy_ecs/critical-section",
+  "bevy_reflect?/critical-section",
+  "bevy_input_focus/critical-section",
+]
+
+## `portable-atomic` provides additional platform support for atomic types and
+## operations, even on targets without native support. 
+portable-atomic = [
+  "bevy_app/portable-atomic",
+  "bevy_ecs/portable-atomic",
+  "bevy_reflect?/portable-atomic",
+  "bevy_input_focus/portable-atomic",
+]
+
+## Uses the `libm` maths library instead of the one provided in `std` and `core`.
+libm = ["bevy_input_focus/libm"]
+
 [dependencies]
 # bevy
-bevy_app = { path = "../bevy_app", version = "0.16.0-dev" }
+bevy_app = { path = "../bevy_app", version = "0.16.0-dev", default-features = false }
 bevy_derive = { path = "../bevy_derive", version = "0.16.0-dev" }
-bevy_ecs = { path = "../bevy_ecs", version = "0.16.0-dev" }
-bevy_reflect = { path = "../bevy_reflect", version = "0.16.0-dev" }
-bevy_input_focus = { path = "../bevy_input_focus", version = "0.16.0-dev" }
+bevy_ecs = { path = "../bevy_ecs", version = "0.16.0-dev", default-features = false }
+bevy_reflect = { path = "../bevy_reflect", version = "0.16.0-dev", default-features = false, optional = true }
+bevy_input_focus = { path = "../bevy_input_focus", version = "0.16.0-dev", default-features = false }
 
-accesskit = "0.17"
+# other
+accesskit = { version = "0.17", default-features = false }
+serde = { version = "1", default-features = false, features = [
+  "alloc",
+], optional = true }
 
 [lints]
 workspace = true

crates/bevy_a11y/src/lib.rs

@@ -4,6 +4,7 @@
     html_logo_url = "https://bevyengine.org/assets/icon.png",
     html_favicon_url = "https://bevyengine.org/assets/icon.png"
 )]
+#![no_std]
 
 //! Accessibility for Bevy
 //!
@@ -13,6 +14,9 @@
 //!
 //! Make sure to use the same version of `accesskit` as Bevy.
 
+#[cfg(feature = "std")]
+extern crate std;
+
 extern crate alloc;
 
 use alloc::sync::Arc;
@@ -27,8 +31,21 @@ use bevy_ecs::{
     schedule::SystemSet,
 };
 
+#[cfg(feature = "bevy_reflect")]
+use {
+    bevy_ecs::reflect::ReflectResource, bevy_reflect::std_traits::ReflectDefault,
+    bevy_reflect::Reflect,
+};
+
+#[cfg(feature = "serialize")]
+use serde::{Deserialize, Serialize};
+
+#[cfg(all(feature = "bevy_reflect", feature = "serialize"))]
+use bevy_reflect::{ReflectDeserialize, ReflectSerialize};
+
 /// Wrapper struct for [`accesskit::ActionRequest`]. Required to allow it to be used as an `Event`.
 #[derive(Event, Deref, DerefMut)]
+#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
 pub struct ActionRequest(pub accesskit::ActionRequest);
 
 /// Resource that tracks whether an assistive technology has requested
@@ -37,6 +54,7 @@ pub struct ActionRequest(pub accesskit::ActionRequest);
 /// Useful if a third-party plugin needs to conditionally integrate with
 /// `AccessKit`
 #[derive(Resource, Default, Clone, Debug, Deref, DerefMut)]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Default, Resource))]
 pub struct AccessibilityRequested(Arc<AtomicBool>);
 
 impl AccessibilityRequested {
@@ -59,6 +77,12 @@ impl AccessibilityRequested {
 /// accessibility updates instead. Without this, the external library and ECS
 /// will generate conflicting updates.
 #[derive(Resource, Clone, Debug, Deref, DerefMut)]
+#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Resource))]
+#[cfg_attr(
+    all(feature = "bevy_reflect", feature = "serialize"),
+    reflect(Serialize, Deserialize)
+)]
 pub struct ManageAccessibilityUpdates(bool);
 
 impl Default for ManageAccessibilityUpdates {
@@ -88,6 +112,7 @@ impl ManageAccessibilityUpdates {
 /// If the entity doesn't have a parent, or if the immediate parent doesn't have
 /// an `AccessibilityNode`, its node will be an immediate child of the primary window.
 #[derive(Component, Clone, Deref, DerefMut)]
+#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
 pub struct AccessibilityNode(pub Node);
 
 impl From<Node> for AccessibilityNode {
@@ -98,6 +123,12 @@ impl From<Node> for AccessibilityNode {
 
 /// Set enum for the systems relating to accessibility
 #[derive(Debug, Hash, PartialEq, Eq, Clone, SystemSet)]
+#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect))]
+#[cfg_attr(
+    all(feature = "bevy_reflect", feature = "serialize"),
+    reflect(Serialize, Deserialize)
+)]
 pub enum AccessibilitySystem {
     /// Update the accessibility tree
     Update,

tools/ci/src/commands/compile_check_no_std.rs

@@ -131,7 +131,7 @@ impl Prepare for CompileCheckNoStdCommand {
                 sh,
                 "cargo check -p bevy_window --no-default-features --features libm,bevy_reflect,serialize --target {target}"
             ),
-            "Please fix compiler errors in output above for bevy_state no_std compatibility.",
+            "Please fix compiler errors in output above for bevy_window no_std compatibility.",
         ));
 
         commands.push(PreparedCommand::new::<Self>(
@@ -147,7 +147,7 @@ impl Prepare for CompileCheckNoStdCommand {
                 sh,
                 "cargo check -p bevy_time --no-default-features --features bevy_reflect,serialize --target {target}"
             ),
-            "Please fix compiler errors in output above for bevy_transform no_std compatibility.",
+            "Please fix compiler errors in output above for bevy_time no_std compatibility.",
         ));
 
         commands.push(PreparedCommand::new::<Self>(
@@ -155,7 +155,15 @@ impl Prepare for CompileCheckNoStdCommand {
                 sh,
                 "cargo check -p bevy_input_focus --no-default-features --features libm,serialize,bevy_reflect --target {target}"
             ),
-            "Please fix compiler errors in output above for bevy_input no_std compatibility.",
+            "Please fix compiler errors in output above for bevy_input_focus no_std compatibility.",
+        ));
+
+        commands.push(PreparedCommand::new::<Self>(
+            cmd!(
+                sh,
+                "cargo check -p bevy_a11y --no-default-features --features libm,serialize,bevy_reflect --target {target}"
+            ),
+            "Please fix compiler errors in output above for bevy_a11y no_std compatibility.",
         ));
 
         commands