bevy/crates/bevy_app/src/lib.rs
Zachary Harrold cc69fdd0c6
Add no_std support to bevy (#17955)
# Objective

- Fixes #15460 (will open new issues for further `no_std` efforts)
- Supersedes #17715

## Solution

- Threaded in new features as required
- Made certain crates optional but default enabled
- Removed `compile-check-no-std` from internal `ci` tool since GitHub CI
can now simply check `bevy` itself now
- Added CI task to check `bevy` on `thumbv6m-none-eabi` to ensure
`portable-atomic` support is still valid [^1]

[^1]: This may be controversial, since it could be interpreted as
implying Bevy will maintain support for `thumbv6m-none-eabi` going
forward. In reality, just like `x86_64-unknown-none`, this is a
[canary](https://en.wiktionary.org/wiki/canary_in_a_coal_mine) target to
make it clear when `portable-atomic` no longer works as intended (fixing
atomic support on atomically challenged platforms). If a PR comes
through and makes supporting this class of platforms impossible, then
this CI task can be removed. I however wager this won't be a problem.

## Testing

- CI

---

## Release Notes

Bevy now has support for `no_std` directly from the `bevy` crate.

Users can disable default features and enable a new `default_no_std`
feature instead, allowing `bevy` to be used in `no_std` applications and
libraries.

```toml
# Bevy for `no_std` platforms
bevy = { version = "0.16", default-features = false, features = ["default_no_std"] }
```

`default_no_std` enables certain required features, such as `libm` and
`critical-section`, and as many optional crates as possible (currently
just `bevy_state`). For atomically-challenged platforms such as the
Raspberry Pi Pico, `portable-atomic` will be used automatically.

For library authors, we recommend depending on `bevy` with
`default-features = false` to allow `std` and `no_std` users to both
depend on your crate. Here are some recommended features a library crate
may want to expose:

```toml
[features]
# Most users will be on a platform which has `std` and can use the more-powerful `async_executor`.
default = ["std", "async_executor"]

# Features for typical platforms.
std = ["bevy/std"]
async_executor = ["bevy/async_executor"]

# Features for `no_std` platforms.
libm = ["bevy/libm"]
critical-section = ["bevy/critical-section"]

[dependencies]
# We disable default features to ensure we don't accidentally enable `std` on `no_std` targets, for example. 
bevy = { version = "0.16", default-features = false }
```

While this is verbose, it gives the maximum control to end-users to
decide how they wish to use Bevy on their platform.

We encourage library authors to experiment with `no_std` support. For
libraries relying exclusively on `bevy` and no other dependencies, it
may be as simple as adding `#![no_std]` to your `lib.rs` and exposing
features as above! Bevy can also provide many `std` types, such as
`HashMap`, `Mutex`, and `Instant` on all platforms. See
`bevy::platform_support` for details on what's available out of the box!

## Migration Guide

- If you were previously relying on `bevy` with default features
disabled, you may need to enable the `std` and `async_executor`
features.
- `bevy_reflect` has had its `bevy` feature removed. If you were relying
on this feature, simply enable `smallvec` and `smol_str` instead.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2025-03-07 03:39:46 +00:00

64 lines
1.7 KiB
Rust

#![cfg_attr(
any(docsrs, docsrs_dep),
expect(
internal_features,
reason = "rustdoc_internals is needed for fake_variadic"
)
)]
#![cfg_attr(any(docsrs, docsrs_dep), feature(doc_auto_cfg, rustdoc_internals))]
#![forbid(unsafe_code)]
#![doc(
html_logo_url = "https://bevyengine.org/assets/icon.png",
html_favicon_url = "https://bevyengine.org/assets/icon.png"
)]
#![no_std]
//! This crate is about everything concerning the highest-level, application layer of a Bevy app.
#[cfg(feature = "std")]
extern crate std;
extern crate alloc;
// Required to make proc macros work in bevy itself.
extern crate self as bevy_app;
mod app;
mod main_schedule;
mod panic_handler;
mod plugin;
mod plugin_group;
mod schedule_runner;
mod sub_app;
mod task_pool_plugin;
#[cfg(all(any(unix, windows), feature = "std"))]
mod terminal_ctrl_c_handler;
pub use app::*;
pub use main_schedule::*;
pub use panic_handler::*;
pub use plugin::*;
pub use plugin_group::*;
pub use schedule_runner::*;
pub use sub_app::*;
pub use task_pool_plugin::*;
#[cfg(all(any(unix, windows), feature = "std"))]
pub use terminal_ctrl_c_handler::*;
/// The app prelude.
///
/// This includes the most common types in this crate, re-exported for your convenience.
pub mod prelude {
#[doc(hidden)]
pub use crate::{
app::{App, AppExit},
main_schedule::{
First, FixedFirst, FixedLast, FixedPostUpdate, FixedPreUpdate, FixedUpdate, Last, Main,
PostStartup, PostUpdate, PreStartup, PreUpdate, RunFixedMainLoop,
RunFixedMainLoopSystem, SpawnScene, Startup, Update,
},
sub_app::SubApp,
NonSendMarker, Plugin, PluginGroup, TaskPoolOptions, TaskPoolPlugin,
};
}