Add no_std support to bevy_transform (#17030)

# Objective

- Contributes to #15460

## Solution

- Added the following features:
  - `std` (default)
  - `alloc` (default)
  - `bevy_reflect` (default)
  - `libm`

## Testing

- CI

## Notes

- `alloc` feature added to allow using this crate in `no_alloc`
environments.
- `bevy_reflect` was previously always enabled when `bevy-support` was
enabled, which isn't how most other crates handle reflection. I've
brought this in line with how most crates gate `bevy_reflect`.

crates/bevy_transform/Cargo.toml

@@ -10,16 +10,16 @@ keywords = ["bevy"]
 
 [dependencies]
 # bevy
-bevy_app = { path = "../bevy_app", version = "0.15.0-dev", optional = true }
-bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev", features = [
-  "bevy_reflect",
+bevy_app = { path = "../bevy_app", version = "0.15.0-dev", default-features = false, optional = true }
+bevy_ecs = { path = "../bevy_ecs", version = "0.15.0-dev", default-features = false, optional = true }
+bevy_hierarchy = { path = "../bevy_hierarchy", version = "0.15.0-dev", default-features = false, features = [
+  "bevy_app",
 ], optional = true }
-bevy_hierarchy = { path = "../bevy_hierarchy", version = "0.15.0-dev", optional = true }
 bevy_math = { path = "../bevy_math", version = "0.15.0-dev", default-features = false }
-bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", features = [
-  "bevy",
+bevy_reflect = { path = "../bevy_reflect", version = "0.15.0-dev", default-features = false, optional = true }
+serde = { version = "1", default-features = false, features = [
+  "derive",
 ], optional = true }
-serde = { version = "1", features = ["derive"], optional = true }
 thiserror = { version = "2", default-features = false }
 derive_more = { version = "1", default-features = false, features = ["from"] }
 
@@ -31,24 +31,51 @@ bevy_math = { path = "../bevy_math", version = "0.15.0-dev", default-features =
 approx = "0.5.1"
 
 [features]
-# Adds normal Bevy impls like deriving components, bundles, reflection, as well as adding
-# systems for transform propagation and more.
-# This exists because it allows opting out of all of this, leaving only a bare-bones transform struct,
-# which enables users to depend on that without needing the larger Bevy dependency tree.
-bevy-support = [
-  "dep:bevy_app",
-  "dep:bevy_ecs",
-  "dep:bevy_hierarchy",
-  "dep:bevy_reflect",
-  "bevy_math/bevy_reflect",
-]
-
 # Turning off default features leaves you with a barebones
 # definition of transform.
-default = ["bevy-support"]
+default = ["std", "bevy-support", "bevy_reflect"]
 
+# Functionality
+
+## Adds normal Bevy impls like deriving components, bundles, reflection, as well as adding
+## systems for transform propagation and more.
+## This exists because it allows opting out of all of this, leaving only a bare-bones transform struct,
+## which enables users to depend on that without needing the larger Bevy dependency tree.
+bevy-support = ["alloc", "dep:bevy_app", "dep:bevy_ecs", "dep:bevy_hierarchy"]
+
+## Adds serialization support through `serde`.
 serialize = ["dep:serde", "bevy_math/serialize"]
 
+## Adds runtime reflection support using `bevy_reflect`.
+bevy_reflect = [
+  "bevy-support",
+  "dep:bevy_reflect",
+  "bevy_math/bevy_reflect",
+  "bevy_ecs/bevy_reflect",
+  "bevy_app/bevy_reflect",
+]
+
+# 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 = [
+  "alloc",
+  "bevy_app?/std",
+  "bevy_ecs?/std",
+  "bevy_hierarchy?/std",
+  "bevy_math/std",
+  "bevy_reflect?/std",
+  "serde?/std",
+]
+
+## Allows access to the `alloc` crate.
+alloc = ["serde?/alloc"]
+
+## Uses the `libm` maths library instead of the one provided in `std` and `core`.
+libm = ["bevy_math/libm"]
+
 [lints]
 workspace = true
 

crates/bevy_transform/src/components/global_transform.rs

@@ -1,13 +1,18 @@
 use core::ops::Mul;
 
 use super::Transform;
-use bevy_math::{Affine3A, Dir3, Isometry3d, Mat4, Quat, Vec3, Vec3A};
-#[cfg(all(feature = "bevy-support", feature = "serialize"))]
-use bevy_reflect::{ReflectDeserialize, ReflectSerialize};
+use bevy_math::{ops, Affine3A, Dir3, Isometry3d, Mat4, Quat, Vec3, Vec3A};
 use derive_more::derive::From;
+
+#[cfg(all(feature = "bevy_reflect", feature = "serialize"))]
+use bevy_reflect::{ReflectDeserialize, ReflectSerialize};
+
 #[cfg(feature = "bevy-support")]
+use bevy_ecs::component::Component;
+
+#[cfg(feature = "bevy_reflect")]
 use {
-    bevy_ecs::{component::Component, reflect::ReflectComponent},
+    bevy_ecs::reflect::ReflectComponent,
     bevy_reflect::{std_traits::ReflectDefault, Reflect},
 };
 
@@ -42,26 +47,27 @@ use {
 /// [transform_example]: https://github.com/bevyengine/bevy/blob/latest/examples/transforms/transform.rs
 #[derive(Debug, PartialEq, Clone, Copy, From)]
 #[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "bevy-support", derive(Component))]
 #[cfg_attr(
-    feature = "bevy-support",
-    derive(Component, Reflect),
+    feature = "bevy_reflect",
+    derive(Reflect),
     reflect(Component, Default, PartialEq, Debug)
 )]
 #[cfg_attr(
-    all(feature = "bevy-support", feature = "serialize"),
+    all(feature = "bevy_reflect", feature = "serialize"),
     reflect(Serialize, Deserialize)
 )]
 pub struct GlobalTransform(Affine3A);
 
 macro_rules! impl_local_axis {
     ($pos_name: ident, $neg_name: ident, $axis: ident) => {
-        #[doc=std::concat!("Return the local ", std::stringify!($pos_name), " vector (", std::stringify!($axis) ,").")]
+        #[doc=core::concat!("Return the local ", core::stringify!($pos_name), " vector (", core::stringify!($axis) ,").")]
         #[inline]
         pub fn $pos_name(&self) -> Dir3 {
             Dir3::new_unchecked((self.0.matrix3 * Vec3::$axis).normalize())
         }
 
-        #[doc=std::concat!("Return the local ", std::stringify!($neg_name), " vector (-", std::stringify!($axis) ,").")]
+        #[doc=core::concat!("Return the local ", core::stringify!($neg_name), " vector (-", core::stringify!($axis) ,").")]
         #[inline]
         pub fn $neg_name(&self) -> Dir3 {
             -self.$pos_name()
@@ -235,7 +241,7 @@ impl GlobalTransform {
         //Formula based on glam's implementation https://github.com/bitshifter/glam-rs/blob/2e4443e70c709710dfb25958d866d29b11ed3e2b/src/f32/affine3a.rs#L290
         let det = self.0.matrix3.determinant();
         Vec3::new(
-            self.0.matrix3.x_axis.length() * det.signum(),
+            self.0.matrix3.x_axis.length() * ops::copysign(1., det),
             self.0.matrix3.y_axis.length(),
             self.0.matrix3.z_axis.length(),
         )

crates/bevy_transform/src/components/transform.rs

@@ -1,11 +1,12 @@
 use super::GlobalTransform;
 use bevy_math::{Affine3A, Dir3, Isometry3d, Mat3, Mat4, Quat, Vec3};
 use core::ops::Mul;
+
 #[cfg(feature = "bevy-support")]
-use {
-    bevy_ecs::{component::Component, prelude::require, reflect::ReflectComponent},
-    bevy_reflect::prelude::*,
-};
+use bevy_ecs::{component::Component, prelude::require};
+
+#[cfg(feature = "bevy_reflect")]
+use {bevy_ecs::reflect::ReflectComponent, bevy_reflect::prelude::*};
 
 /// Describe the position of an entity. If the entity has a parent, the position is relative
 /// to its parent position.
@@ -38,14 +39,14 @@ use {
 /// [transform_example]: https://github.com/bevyengine/bevy/blob/latest/examples/transforms/transform.rs
 #[derive(Debug, PartialEq, Clone, Copy)]
 #[cfg_attr(feature = "serialize", derive(serde::Serialize, serde::Deserialize))]
+#[cfg_attr(feature = "bevy-support", derive(Component), require(GlobalTransform))]
 #[cfg_attr(
-    feature = "bevy-support",
-    derive(Component, Reflect),
-    require(GlobalTransform),
+    feature = "bevy_reflect",
+    derive(Reflect),
     reflect(Component, Default, PartialEq, Debug)
 )]
 #[cfg_attr(
-    all(feature = "bevy-support", feature = "serialize"),
+    all(feature = "bevy_reflect", feature = "serialize"),
     reflect(Serialize, Deserialize)
 )]
 pub struct Transform {

crates/bevy_transform/src/lib.rs

@@ -4,6 +4,10 @@
     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)]
+
+#[cfg(feature = "alloc")]
+extern crate alloc;
 
 #[cfg(feature = "bevy-support")]
 pub mod commands;

crates/bevy_transform/src/plugins.rs

@@ -3,10 +3,13 @@ use bevy_ecs::schedule::{IntoSystemConfigs, IntoSystemSetConfigs, SystemSet};
 use bevy_hierarchy::ValidParentCheckPlugin;
 
 use crate::{
-    prelude::{GlobalTransform, Transform},
+    components::GlobalTransform,
     systems::{propagate_transforms, sync_simple_transforms},
 };
 
+#[cfg(feature = "bevy_reflect")]
+use crate::components::Transform;
+
 /// Set enum for the systems relating to transform propagation
 #[derive(Debug, Hash, PartialEq, Eq, Clone, SystemSet)]
 pub enum TransformSystem {
@@ -25,9 +28,11 @@ impl Plugin for TransformPlugin {
         #[derive(Debug, Hash, PartialEq, Eq, Clone, SystemSet)]
         struct PropagateTransformsSet;
 
+        #[cfg(feature = "bevy_reflect")]
         app.register_type::<Transform>()
-            .register_type::<GlobalTransform>()
-            .add_plugins(ValidParentCheckPlugin::<GlobalTransform>::default())
+            .register_type::<GlobalTransform>();
+
+        app.add_plugins(ValidParentCheckPlugin::<GlobalTransform>::default())
             .configure_sets(
                 PostStartup,
                 PropagateTransformsSet.in_set(TransformSystem::TransformPropagate),

crates/bevy_transform/src/systems.rs

@@ -1,4 +1,5 @@
 use crate::components::{GlobalTransform, Transform};
+use alloc::vec::Vec;
 use bevy_ecs::{
     change_detection::Ref,
     prelude::{Changed, DetectChanges, Entity, Query, With, Without},

tools/ci/src/commands/compile_check_no_std.rs

@@ -134,6 +134,14 @@ impl Prepare for CompileCheckNoStdCommand {
             "Please fix compiler errors in output above for bevy_state no_std compatibility.",
         ));
 
+        commands.push(PreparedCommand::new::<Self>(
+            cmd!(
+                sh,
+                "cargo check -p bevy_transform --no-default-features --features bevy-support,serialize,libm --target {target}"
+            ),
+            "Please fix compiler errors in output above for bevy_transform no_std compatibility.",
+        ));
+
         commands
     }
 }