Registering bevy as a Tool

When you run bevy_lint on a project, rustc knows an exact list of all bevy:: lints registered. With this it can detect that bevy::missing_reflect is valid and bevy::uh_oh isn't, and emit a corresponding warning.

When you run normal cargo check, however, it does not know about any bevy:: lints. In order to avoid erroring on all usages of bevy::, but to still provide good diagnostics on typos, the #![register_tool(...)] attribute was introduced.

// Note that this is nightly-only. We'll get to that in a second!
#![register_tool(bevy)]

Using #![register_tool(bevy)] tells the compiler that bevy is a valid name in attributes, even if it does not know what bevy is.¹ When cargo check now runs over a project with #[warn(bevy::lint_name)], it will simply skip it instead of emitting an error. (But running bevy_lint will still detect and check this attribute as normal.)

If you wish to refer to a bevy lint at all in your code (usually to toggle it), you must add #![register_tool(bevy)] to each crate root. Unfortunately, #![register_tool(...)] is currently unstable, meaning you need to add #![feature(register_tool)] to your code as well. This isn't an issue if you detect when bevy_lint is enabled, since it is guaranteed to check your code using nightly Rust.

// When `bevy_lint` is used, enable the `register_tool` feature and register `bevy` as a tool.
#![cfg_attr(bevy_lint, feature(register_tool), register_tool(bevy))]

Tip

If your project already uses nightly Rust, you can forego the #[cfg_attr(bevy_lint, ...)] attributes and write #![feature(register_tool)] and #![register_tool(bevy)] directly! Cool!

1. If you've ever used #[rustfmt::skip] in your code, this is how rustc avoids erroring on it. However unlike the bevy namespace, rustfmt is registered automatically without a need for #![register_tool(rustfmt)] due to it being an official tool. ↩