Since Clippy v0.0.97 and before it was shipped with rustup, Clippy implicitly added a feature = "cargo-clippy" config¹ when linting your code with cargo clippy.

Back in the day (2016) this was necessary to allow, warn or deny Clippy lints using attributes:

#[cfg_attr(feature = "cargo-clippy", allow(clippy_lint_name))]

Doing this hasn't been necessary for a long time. Today, Clippy users will set lint levels with tool lint attributes using the clippy:: prefix:

#[allow(clippy::lint_name)]

The implicit feature = "cargo-clippy" has only been kept for backwards compatibility, but will be deprecated in upcoming nightlies and later in 1.78.0.

Alternative

As there is a rare use case for conditional compilation depending on Clippy, we will provide an alternative. So in the future (1.78.0) you will be able to use:

#[cfg(clippy)]

Transitioning

Should you only use stable toolchains, you can wait with the transition until Rust 1.78.0 (2024-05-02) is released.

Should you have instances of feature = "cargo-clippy" in your code base, you will see a warning from the new Clippy lint clippy::deprecated_clippy_cfg_attr available in the latest nightly Clippy. This lint can automatically fix your code. So if you should see this lint triggering, just run:

cargo clippy --fix -- -Aclippy::all -Wclippy::deprecated_clippy_cfg_attr

This will fix all instances in your code.

In addition, check your .cargo/config file for:

[target.'cfg(feature = "cargo-clippy")']
rustflags = ["-Aclippy::..."]

If you have this config, you will have to update it yourself, by either changing it to cfg(clippy) or taking this opportunity to transition to setting lint levels in Cargo.toml directly.

Motivation for Deprecation

Currently, there's a call for testing, in order to stabilize checking conditional compilation at compile time, aka cargo check -Zcheck-cfg. If we were to keep the feature = "cargo-clippy" config, users would start seeing a lot of warnings on their feature = "cargo-clippy" conditions. To work around this, they would either need to allow the lint or have to add a dummy feature to their Cargo.toml in order to silence those warnings:

[features]
cargo-clippy = []

We didn't think this would be user friendly, and decided that instead we want to deprecate the implicit feature = "cargo-clippy" config and replace it with the clippy config.