Add no_std support to bevy_input (#16995)

# Objective

- Contributes to #15460

## Solution

- Added the following features:
  - `std` (default)
  - `smol_str` (default)
  - `portable-atomic`
  - `critical-section`
  - `libm`
- Fixed an existing issue where `bevy_reflect` wasn't properly feature
gated.

## Testing

- CI

## Notes

- There were some minor issues with `bevy_math` and `bevy_ecs` noticed
in this PR which I have also resolved here. I can split these out if
desired, but I've left them here for now as they're very small changes
and I don't consider this PR itself to be very controversial.
- `libm`, `portable-atomic`, and `critical-section` are shortcuts to
enable the relevant features in dependencies, making the usage of this
crate on atomically challenged platforms possible and simpler.
- `smol_str` is gated as it doesn't support atomically challenged
platforms (e.g., Raspberry Pi Pico). I have an issue and a
[PR](https://github.com/rust-analyzer/smol_str/pull/91) to discuss this
upstream.

crates/bevy_ecs/src/name.rs

@@ -13,9 +13,12 @@ use core::{
 };
 
 #[cfg(feature = "serialize")]
-use serde::{
+use {
+    alloc::string::ToString,
+    serde::{
         de::{Error, Visitor},
         Deserialize, Deserializer, Serialize, Serializer,
+    },
 };
 
 #[cfg(feature = "bevy_reflect")]

crates/bevy_input/Cargo.toml

@@ -9,36 +9,72 @@ license = "MIT OR Apache-2.0"
 keywords = ["bevy"]
 
 [features]
-default = ["bevy_reflect"]
+default = ["std", "bevy_reflect", "bevy_ecs/async_executor", "smol_str"]
+
+# Functionality
+
+## Adds runtime reflection support using `bevy_reflect`.
 bevy_reflect = [
   "dep:bevy_reflect",
   "bevy_app/bevy_reflect",
   "bevy_ecs/bevy_reflect",
   "bevy_math/bevy_reflect",
 ]
-serialize = ["serde", "smol_str/serde"]
+
+## Adds serialization support through `serde`.
+serialize = [
+  "serde",
+  "smol_str/serde",
+  "bevy_ecs/serialize",
+  "bevy_math/serialize",
+]
+
+## Uses the small-string optimization provided by `smol_str`.
+smol_str = ["dep:smol_str", "bevy_reflect/smol_str"]
+
+# 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_math/std",
+  "bevy_utils/std",
+  "bevy_reflect/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"]
+
+## `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"]
+
+## Uses the `libm` maths library instead of the one provided in `std` and `core`.
+libm = ["bevy_math/libm"]
 
 [dependencies]
 # bevy
 bevy_app = { path = "../bevy_app", version = "0.15.0-dev", default-features = false }
-bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev", default-features = false, features = [
+bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev", default-features = false }
-  "serialize",
+bevy_math = { path = "../bevy_math", version = "0.15.0-dev", default-features = false }
-] }
+bevy_utils = { path = "../bevy_utils", version = "0.15.0-dev", default-features = false }
-bevy_math = { path = "../bevy_math", version = "0.15.0-dev", default-features = false, features = [
-  "rand",
-  "serialize",
-] }
-bevy_utils = { path = "../bevy_utils", version = "0.15.0-dev" }
 bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", features = [
   "glam",
-  "smol_str",
+], default-features = false, optional = true }
-], optional = true }
 
 # other
-serde = { version = "1", features = ["derive"], optional = true }
+serde = { version = "1", features = [
+  "alloc",
+  "derive",
+], default-features = false, optional = true }
 thiserror = { version = "2", default-features = false }
 derive_more = { version = "1", default-features = false, features = ["from"] }
-smol_str = "0.2"
+smol_str = { version = "0.2", default-features = false, optional = true }
+log = { version = "0.4", default-features = false }
 
 [lints]
 workspace = true

crates/bevy_input/src/gamepad.rs

@@ -1,6 +1,7 @@
 //! The gamepad input functionality.
 
 use crate::{Axis, ButtonInput, ButtonState};
+use alloc::string::String;
 #[cfg(feature = "bevy_reflect")]
 use bevy_ecs::prelude::ReflectComponent;
 use bevy_ecs::{
@@ -12,16 +13,15 @@ use bevy_ecs::{
     prelude::require,
     system::{Commands, Query},
 };
+use bevy_math::ops;
 use bevy_math::Vec2;
 #[cfg(feature = "bevy_reflect")]
 use bevy_reflect::{std_traits::ReflectDefault, Reflect};
 #[cfg(all(feature = "serialize", feature = "bevy_reflect"))]
 use bevy_reflect::{ReflectDeserialize, ReflectSerialize};
-use bevy_utils::{
+use bevy_utils::{Duration, HashMap};
-    tracing::{info, warn},
-    Duration, HashMap,
-};
 use derive_more::derive::From;
+use log::{info, warn};
 use thiserror::Error;
 
 /// A gamepad event.
@@ -54,11 +54,11 @@ pub enum GamepadEvent {
 /// the in-frame relative ordering of events is important.
 ///
 /// This event type is used by `bevy_input` to feed its components.
-#[derive(Event, Debug, Clone, PartialEq, Reflect, From)]
+#[derive(Event, Debug, Clone, PartialEq, From)]
-#[reflect(Debug, PartialEq)]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug, PartialEq))]
+#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(
-    feature = "serialize",
+    all(feature = "serialize", feature = "bevy_reflect"),
-    derive(serde::Serialize, serde::Deserialize),
     reflect(Serialize, Deserialize)
 )]
 pub enum RawGamepadEvent {
@@ -71,11 +71,11 @@ pub enum RawGamepadEvent {
 }
 
 /// [`GamepadButton`] changed event unfiltered by [`GamepadSettings`]
-#[derive(Event, Debug, Copy, Clone, PartialEq, Reflect)]
+#[derive(Event, Debug, Copy, Clone, PartialEq)]
-#[reflect(Debug, PartialEq)]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug, PartialEq))]
+#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(
-    feature = "serialize",
+    all(feature = "serialize", feature = "bevy_reflect"),
-    derive(serde::Serialize, serde::Deserialize),
     reflect(Serialize, Deserialize)
 )]
 pub struct RawGamepadButtonChangedEvent {
@@ -99,11 +99,11 @@ impl RawGamepadButtonChangedEvent {
 }
 
 /// [`GamepadAxis`] changed event unfiltered by [`GamepadSettings`]
-#[derive(Event, Debug, Copy, Clone, PartialEq, Reflect)]
+#[derive(Event, Debug, Copy, Clone, PartialEq)]
-#[reflect(Debug, PartialEq)]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug, PartialEq))]
+#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(
-    feature = "serialize",
+    all(feature = "serialize", feature = "bevy_reflect"),
-    derive(serde::Serialize, serde::Deserialize),
     reflect(Serialize, Deserialize)
 )]
 pub struct RawGamepadAxisChangedEvent {
@@ -128,11 +128,11 @@ impl RawGamepadAxisChangedEvent {
 
 /// A Gamepad connection event. Created when a connection to a gamepad
 /// is established and when a gamepad is disconnected.
-#[derive(Event, Debug, Clone, PartialEq, Reflect)]
+#[derive(Event, Debug, Clone, PartialEq)]
-#[reflect(Debug, PartialEq)]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug, PartialEq))]
+#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(
-    feature = "serialize",
+    all(feature = "serialize", feature = "bevy_reflect"),
-    derive(serde::Serialize, serde::Deserialize),
     reflect(Serialize, Deserialize)
 )]
 pub struct GamepadConnectionEvent {
@@ -163,11 +163,11 @@ impl GamepadConnectionEvent {
 }
 
 /// [`GamepadButton`] event triggered by a digital state change
-#[derive(Event, Debug, Clone, Copy, PartialEq, Eq, Reflect)]
+#[derive(Event, Debug, Clone, Copy, PartialEq, Eq)]
-#[reflect(Debug, PartialEq)]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug, PartialEq))]
+#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(
-    feature = "serialize",
+    all(feature = "serialize", feature = "bevy_reflect"),
-    derive(serde::Serialize, serde::Deserialize),
     reflect(Serialize, Deserialize)
 )]
 pub struct GamepadButtonStateChangedEvent {
@@ -191,11 +191,11 @@ impl GamepadButtonStateChangedEvent {
 }
 
 /// [`GamepadButton`] event triggered by an analog state change
-#[derive(Event, Debug, Clone, Copy, PartialEq, Reflect)]
+#[derive(Event, Debug, Clone, Copy, PartialEq)]
-#[reflect(Debug, PartialEq)]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug, PartialEq))]
+#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
 #[cfg_attr(
-    feature = "serialize",
+    all(feature = "serialize", feature = "bevy_reflect"),
-    derive(serde::Serialize, serde::Deserialize),
     reflect(Serialize, Deserialize)
 )]
 pub struct GamepadButtonChangedEvent {
@@ -222,11 +222,11 @@ impl GamepadButtonChangedEvent {
 }
 
 /// [`GamepadAxis`] event triggered by an analog state change
-#[derive(Event, Debug, Clone, Copy, PartialEq, Reflect)]
+#[derive(Event, Debug, Clone, Copy, PartialEq)]
-#[reflect(Debug, PartialEq)]
+#[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "bevy_reflect", derive(Reflect), reflect(Debug, PartialEq))]
 #[cfg_attr(
-    feature = "serialize",
+    all(feature = "bevy_reflect", feature = "serialize"),
-    derive(serde::Serialize, serde::Deserialize),
     reflect(Serialize, Deserialize)
 )]
 pub struct GamepadAxisChangedEvent {
@@ -1232,7 +1232,7 @@ impl AxisSettings {
             return true;
         }
 
-        f32::abs(new_value - old_value.unwrap()) > self.threshold
+        ops::abs(new_value - old_value.unwrap()) > self.threshold
     }
 
     /// Filters the `new_value` based on the `old_value`, according to the [`AxisSettings`].
@@ -1307,7 +1307,7 @@ impl ButtonAxisSettings {
             return true;
         }
 
-        f32::abs(new_value - old_value.unwrap()) > self.threshold
+        ops::abs(new_value - old_value.unwrap()) > self.threshold
     }
 
     /// Filters the `new_value` based on the `old_value`, according to the [`ButtonAxisSettings`].

crates/bevy_input/src/keyboard.rs

@@ -72,8 +72,14 @@ use bevy_ecs::{
     event::{Event, EventReader},
     system::ResMut,
 };
+
 #[cfg(feature = "bevy_reflect")]
 use bevy_reflect::Reflect;
+
+#[cfg(not(feature = "smol_str"))]
+use alloc::string::String as SmolStr;
+
+#[cfg(feature = "smol_str")]
 use smol_str::SmolStr;
 
 #[cfg(all(feature = "serialize", feature = "bevy_reflect"))]

crates/bevy_input/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"
 )]
+#![cfg_attr(not(feature = "std"), no_std)]
 
 //! Input functionality for the [Bevy game engine](https://bevyengine.org/).
 //!
@@ -11,6 +12,8 @@
 //!
 //! `bevy` currently supports keyboard, mouse, gamepad, and touch inputs.
 
+extern crate alloc;
+
 mod axis;
 mod button_input;
 /// Common run conditions

crates/bevy_math/Cargo.toml

@@ -25,7 +25,7 @@ approx = { version = "0.5", default-features = false, optional = true }
 rand = { version = "0.8", default-features = false, optional = true }
 rand_distr = { version = "0.4.3", optional = true }
 smallvec = { version = "1.11" }
-bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", features = [
+bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", default-features = false, features = [
   "glam",
 ], optional = true }
 variadics_please = "1.1"
@@ -52,6 +52,7 @@ std = [
   "approx?/std",
   "rand?/std",
   "rand_distr?/std",
+  "bevy_reflect?/std",
 ]
 alloc = [
   "itertools/use_alloc",
@@ -76,8 +77,8 @@ debug_glam_assert = ["glam/debug-glam-assert"]
 rand = ["dep:rand", "dep:rand_distr", "glam/rand"]
 # Include code related to the Curve trait
 curve = []
-# Enable bevy_reflect (requires std)
+# Enable bevy_reflect (requires alloc)
-bevy_reflect = ["dep:bevy_reflect", "std"]
+bevy_reflect = ["dep:bevy_reflect", "alloc"]
 
 [lints]
 workspace = true

tools/ci/src/commands/compile_check_no_std.rs

@@ -118,6 +118,14 @@ impl Prepare for CompileCheckNoStdCommand {
             "Please fix compiler errors in output above for bevy_hierarchy no_std compatibility.",
         ));
 
+        commands.push(PreparedCommand::new::<Self>(
+            cmd!(
+                sh,
+                "cargo check -p bevy_input --no-default-features --features libm,serialize,bevy_reflect --target {target}"
+            ),
+            "Please fix compiler errors in output above for bevy_input no_std compatibility.",
+        ));
+
         commands
     }
 }