cargo-unused-allow

Detect unused #[allow(...)] attributes in Rust projects.

How it works

1. Temporarily replaces every #[allow(...)] / #![allow(...)] with #[expect(...)] / #![expect(...)] in your source files.
2. Runs cargo clippy --message-format=json -- -Wunfulfilled-lint-expectations once.
3. Parses unfulfilled_lint_expectations diagnostics — each one corresponds to an #[allow] that was suppressing nothing.
4. Restores all original files (even on failure or panic).

Why?

Rust 1.81 stabilized #[expect(...)], which warns you when the suppressed lint no longer fires — but many projects still carry #[allow] attributes added before #[expect] existed, or out of habit. Over time, some of these become stale: the guarded code is refactored away, the lint rule changes, or the attribute was copy-pasted without thought. This is especially common in larger codebases. Stale #[allow]s silently hide real warnings and mask code-quality regressions, yet finding them manually is tedious.

cargo-unused-allow automates this. It detects every #[allow] that suppresses nothing — useful as a one-time cleanup, a CI gate, or a stepping stone toward migrating to #[expect].

Requirements

• Rust toolchain 1.81 or later (for #[expect] support)
• clippy (rustup component add clippy)

Installation

From local source

cargo install --path .

From crates.io

cargo install cargo-unused-allow

From GitHub

cargo install --git https://github.com/lapla-cogito/cargo-unused-allow

Usage

# Run in any Rust project directory
cd /path/to/your/rust/project
# Basic detection
cargo-unused-allow
# Also check tests, examples, and benches
cargo-unused-allow --all-targets
# Automatically remove unused #[allow] attributes
cargo-unused-allow --fix
# Exclude specific lints from detection
cargo-unused-allow --exclude dead_code --exclude unused_imports
# Combine options
cargo-unused-allow --all-targets --fix --exclude dead_code

# Pass extra arguments to cargo clippy (after --)
cargo-unused-allow -- --workspace
cargo-unused-allow -- --package my-crate
cargo-unused-allow -- --workspace --features serde
cargo-unused-allow --all-targets -- --workspace

When installed via cargo install, you can also invoke it as a cargo subcommand:

cargo unused-allow --all-targets

Options

$ cargo unused-allow --help

Detect unused #[allow(...)] attributes in Rust projects

Usage: cargo-unused-allow [OPTIONS] [-- <CLIPPY_ARGS>...]

Arguments:
  [CLIPPY_ARGS]...  Extra arguments passed through to `cargo clippy` (specify after --)

Options:
      --all-targets     Check all targets (tests, examples, etc...)
      --fix             Automatically remove unused #[allow(...)] attributes from source files
      --exclude <LINT>  Lint names to exclude from detection (can be specified multiple times)
  -h, --help            Print help
  -V, --version         Print version

Exit codes

Example output

See the examples directory for sample output. *.rs files are the original sources, *.rs.output files contain the tool's output, and *.rs.fixed files are generated with --fix.

--fix behavior

When --fix is specified, the tool modifies source files directly:

• Single-lint attributes like #[allow(dead_code)] are removed entirely (including the line).
• Multi-lint attributes like #[allow(dead_code, unused_variables)] are rewritten to keep only the lints that are still needed (e.g., #[allow(unused_variables)]).
• Inner attributes like #![allow(...)] are handled the same way.
• cfg_attr-wrapped attributes like #[cfg_attr(feature = "foo", allow(dead_code))] are removed entirely when all lints are unused, or rewritten to keep remaining lints (e.g., #[cfg_attr(feature = "foo", allow(unused_imports))]).
• Indentation and surrounding code are preserved.

--exclude behavior

You can exclude specific lint names from detection. This is useful when you intentionally keep certain #[allow] attributes (e.g., for forward compatibility):

# Ignore unused dead_code and unused_imports allows
cargo-unused-allow --exclude dead_code --exclude unused_imports

The --exclude flag can be specified multiple times. Clippy lints use their full path:

cargo-unused-allow --exclude clippy::needless_return

Try with included examples

The repository includes example files in examples/ that demonstrate detection:

# From the repository root — detect only
cargo-unused-allow --all-targets

# Detect and auto-fix
cargo-unused-allow --all-targets --fix

License

MIT