rrubocop

Rust RuboCop drop-in replacement — same CLI, config, and offense output, rewritten in Rust for speed. Point it at an existing Ruby project and use it like RuboCop.

One binary — runs even without Ruby on the system, and the same way regardless of rbenv, rvm, or system Ruby. Uses tree-sitter; no Ruby runtime required for linting. Simple ERB in configs (literals, <% var = … %> / <%= var %>, ENV[…] / ENV.fetch(…)) expands natively without Ruby; unsupported ERB falls back to ruby / bundle exec ruby, matching RuboCop.

Drop-in parity: reads your existing .rubocop.yml, emits RuboCop-like text/JSON, supports -a/-A autocorrect, and grows cop coverage over time.

Baseline (shown in --help / --version): rubocop 1.84.2 with rubocop-rails 2.34.3, rubocop-performance 1.26.1, rubocop-rspec 3.9.0, rubocop-rspec_rails 2.32.0, rubocop-factory_bot 2.28.0 — pinned in src/resources/baseline.json.

Install

brew install adrianov/rrubocop/rrubocop

cargo install rrubocop

macOS (.tar.gz from GitHub Releases; binary + man):

# Apple Silicon — use the *-x86_64-apple-darwin.tar.gz asset on Intel Macs
curl -LO https://github.com/adrianov/rrubocop/releases/download/v0.7.2/rrubocop-0.7.2-aarch64-apple-darwin.tar.gz
tar -xzf rrubocop-0.7.2-aarch64-apple-darwin.tar.gz
sudo cp rrubocop-0.7.2-aarch64-apple-darwin/rrubocop /usr/local/bin/
sudo mkdir -p /usr/local/share/man/man1
sudo cp rrubocop-0.7.2-aarch64-apple-darwin/rrubocop.1 /usr/local/share/man/man1/

Ubuntu / Debian (.deb from GitHub Releases; amd64, Ubuntu 22.04+ / Debian bookworm+):

# example for v0.7.2 — use the asset name from the release page
curl -LO https://github.com/adrianov/rrubocop/releases/download/v0.7.2/rrubocop_0.7.2-1_amd64.deb
sudo dpkg -i rrubocop_0.7.2-1_amd64.deb
man rrubocop

rrubocop [OPTIONS] [PATH]...

Features

• Config — RuboCop-compatible resolution: walk-up discovery, inherit_from / inherit_gem / require/plugins, inherit_mode (merge/override), nested .rubocop.yml overrides, DisabledByDefault, NewCops / Enabled: pending, plus per-cop Enabled / Exclude / Include / options; simple ERB in YAML expands natively (Ruby only for unsupported tags)
• Autocorrect — -a (safe) / -A (all)
• Output — progress (marks stream as files finish), text, json, github, quiet, files, … (TTY color like RuboCop; --color / --no-color)
• Directives — # rubocop:disable / enable
• Parser — tree-sitter-ruby (no Prism / no CRuby)
• Cache — content-addressed cache.redb under $RRUBOCOP_CACHE_DIR or $XDG_CACHE_HOME/rrubocop / ~/.cache/rrubocop (same style as abcop); --no-cache disables

Reference implementations: nitrocop (architecture & fixtures), upstream RuboCop.

Built-in cops

Departments grow breadth-first from common RuboCop plugin sets (nitrocop / gem sources). Notable coverage:

Use rrubocop --list-cops for the full registered set, and rrubocop --list-autocorrectable-cops for cops with -a/-A support (~170+ with autocorrect so far; Layout nearly complete; Style/Lint/Rails/RSpec growing).

Usage

rrubocop                         # lint .
rrubocop app lib                 # paths
rrubocop -f json .               # JSON offenses
rrubocop -a .                    # safe autocorrect
rrubocop -A .                    # all autocorrect
rrubocop --only Metrics/AbcSize lib
rrubocop --list-cops
rrubocop -L                      # list target files
rrubocop -F 10                   # stop after 10 offenses (off by default; `-F` = 1)
                                 # with `-a`/`-A`, N is non-autocorrectable offenses only

Exit codes: 0 clean, 1 offenses at/above --fail-level, 2 error.

Caching

Content-addressed cache under $RRUBOCOP_CACHE_DIR (or $XDG_CACHE_HOME/rrubocop / ~/.cache/rrubocop). Keys cover contents, version, rule revision, --only/--except, config fingerprint, and path. Auto-pruned to 20 000 entries; --no-cache disables. Autocorrect runs bypass the cache. Nothing is written inside the project.

Benchmarks

Cold lint (cache off) on a large Rails codebase (~3.8k Ruby files), same host:

rrubocop is ≈ 22× faster wall clock than RuboCop (156.6s / 7.0s) on the same clean result. RuboCop user time was 155s; rrubocop used 71s of CPU across cores.

nitrocop caveat: out of the box it did not honor the same disabled cops / custom rules / gem configs as bundle exec rubocop (e.g. failed inherit_gem load, skipped/unimplemented cops), so it reported ~21k false positives vs RuboCop/rrubocop’s clean run. Matching that baseline needs extra setup (--migrate, plugin/config wiring). Treat the 8.9s figure as raw throughput only, not drop-in parity.

Cold lint (cache off) on rails/rails (main, RuboCop 1.79.2 via bundle exec), same host (4 cores), both clean (0 offenses). Two runs averaged:

≈ 12× faster wall clock (67.254s / 5.668s). RuboCop user time was 66.9s; rrubocop used 20.2s of CPU across cores.

Same host, cold no-cache, offense-set parity on Active Support and Active Record (fp=0, fn=0 on shared .rb files):

Cold lint on a fresh rails new app (Rails 8.1.3.1, default rubocop-rails-omakase via inherit_gem, RuboCop 1.90.0 via bundle exec), plus scaffold/model/mailer/job generators (41 identical target files). Offense-set parity fp=0, fn=0 (both clean). Two-run average:

Cross-test vs nitrocop

With a local nitrocop build:

testdata/cross_test_nitrocop.py /path/to/fixture_dir

Compares (path, line, cop_name) offense sets.

License

GPL-3.0-or-later. See NOTICE for MIT attribution of nitrocop-derived design/logic.