Tooling: rustfmt, Clippy, docs and editions

Why tools matter

Professional Rust teams rarely argue about style or catch simple mistakes in code review, because tools do it automatically. Rust ships a standard set of tools that every project uses the same way, so you can join any Rust codebase and feel at home.

rustfmt: one style for everyone

cargo fmt            # format the whole project
cargo fmt --check    # only check; fails if anything is not formatted (for CI)

Everyone uses the same default style, so code from any project looks familiar. Set your editor to format on save. You can adjust a few options in a rustfmt.toml file, but most teams keep the defaults.

Clippy: a friendly expert reviewer

Clippy is a linter: a tool that looks for code that compiles but is likely wrong, slow or not idiomatic (not in the usual Rust style). It has hundreds of checks, called lints, each with an explanation and usually a suggested fix.

cargo clippy
cargo clippy -- -D warnings   # treat every warning as an error (for CI)

warning: this `if` has identical blocks
warning: using `clone` on type `u32` which implements the `Copy` trait
warning: length comparison to zero
  help: using `is_empty` is clearer and more explicit: `v.is_empty()`

Other cargo tools

Security-minded teams also use community tools such as cargo-audit, which checks Cargo.lock against the RustSec database of known vulnerable crate versions. Install it with cargo install cargo-audit and run cargo audit.

Profiles

[profile.release]
opt-level = 3        # the default for release
lto = true           # link-time optimisation: smaller, faster, slower to build
codegen-units = 1    # better optimisation, slower build

Editions

An edition is a set of language rules chosen per crate in Cargo.toml (edition = "2024"). Editions let Rust fix old design choices without breaking existing code: crates on different editions still work together in one program. Editions so far: 2015, 2018, 2021 and 2024 (released with Rust 1.85 in February 2025).

cargo fix --edition     # apply automatic fixes before switching
# then change edition = "2021" to edition = "2024" in Cargo.toml
cargo build

A simple CI routine

CI (continuous integration) means a server runs your checks automatically on every push or pull request. A typical Rust CI job runs four commands; if any fails, the change is not merged.

cargo fmt --check
cargo clippy --all-targets -- -D warnings
cargo test
cargo build --release

Common mistakes

• Ignoring Clippy warnings for months until there are hundreds. Fix them as they appear.
• Silencing a lint with #[allow(...)] without a comment explaining why.
• Not committing Cargo.lock for applications, so CI builds different versions than your laptop.
• Measuring speed with cargo run (debug). Use --release.