# 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>
# Objective
We want to deny the following lints:
* `clippy::allow_attributes` - Because there's no reason to
`#[allow(...)]` an attribute if it wouldn't lint against anything; you
should always use `#[expect(...)]`
* `clippy::allow_attributes_without_reason` - Because documenting the
reason for allowing/expecting a lint is always good
## Solution
Set the `clippy::allow_attributes` and
`clippy::allow_attributes_without_reason` lints to `deny`, and bring
`bevy_tasks` in line with the new restrictions.
No code changes have been made - except if a lint that was previously
`allow(...)`'d could be removed via small code changes. For example,
`unused_variables` can be handled by adding a `_` to the beginning of a
field's name.
## Testing
I ran `cargo clippy`, and received no errors.
# Objective
- Resolve several warnings encountered when compiling for `no_std`
around `dead_code`
- Fix compatibility with `wasm32-unknown-unknown` when using `no_std`
(identified by Sachymetsu on
[Discord](https://discord.com/channels/691052431525675048/692572690833473578/1323365426901549097))
## Solution
- Removed some unused imports
- Added `allow(dead_code)` for certain private items when compiling on
`no_std`
- Fixed `bevy_app` and `bevy_tasks` compatibility with WASM when
compiling without `std` by appropriately importing `Box` and feature
gating panic unwinding
## Testing
- CI
# Objective
- Contributes to #15460
## Solution
- Added the following features:
- `std` (default)
- `async_executor` (default)
- `edge_executor`
- `critical-section`
- `portable-atomic`
- Added [`edge-executor`](https://crates.io/crates/edge-executor) as a
`no_std` alternative to `async-executor`.
- Updated the `single_threaded_task_pool` to work in `no_std`
environments by gating its reliance on `thread_local`.
## Testing
- Added to `compile-check-no-std` CI command
## Notes
- In previous iterations of this PR, a custom `async-executor`
alternative was vendored in. This raised concerns around maintenance and
testing. In this iteration, an existing version of that same vendoring
is now used, but _only_ in `no_std` contexts. For existing `std`
contexts, the original `async-executor` is used.
- Due to the way statics work, certain `TaskPool` operations have added
restrictions around `Send`/`Sync` in `no_std`. This is because there
isn't a straightforward way to create a thread-local in `no_std`. If
these added constraints pose an issue we can revisit this at a later
date.
- If a user enables both the `async_executor` and `edge_executor`
features, we will default to using `async-executor`. Since enabling
`async_executor` requires `std`, we can safely assume we are in an `std`
context and use the original library.
---------
Co-authored-by: Mike <2180432+hymm@users.noreply.github.com>
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
