Cargo Fast Format (cargo-ff)

Drop-in replacement for cargo fmt. Same flags, byte-identical file output, ~5.5× faster on large workspaces by parallelizing across crates.

Install

cargo install --locked cargo-ff

Usage

Same flags as cargo fmt:

cargo +nightly ff              # format the current package
cargo +nightly ff --all        # format every workspace member
cargo +nightly ff --check      # check only, exit non-zero on diff
cargo +nightly ff -p mycrate   # format specific package(s)

Pre-commit hook

To make git commit fail on unformatted files:

[ -f .git/hooks/pre-commit ] || printf '#!/usr/bin/env sh\n' > .git/hooks/pre-commit
echo 'cargo +nightly ff --check --all || exit' >> .git/hooks/pre-commit
chmod +x .git/hooks/pre-commit

Experimental mtime cache

--ff-experimental-cache records each crate's *.rs mtimes after a successful run. On the next run, crates whose fingerprint is unchanged are not dispatched to rustfmt at all. ~5× speedup on a clean tree.

cargo +nightly ff --all --ff-experimental-cache

Cache lives at ~/.cache/cargo-ff/fingerprints.tsv, salted by the rustfmt --version output and the workspace-root .rustfmt.toml. A mismatch on either invalidates everything.

Soundness caveat: cross-crate #[path = "../other/foo.rs"] references aren't tracked. If the external file changes, we may falsely skip.