# RuboCop — Ruby Static Code Analyzer and Formatter

> A Ruby static code analyzer and formatter based on the community Ruby style guide, with auto-correction and a rich ecosystem of extensions.

## Install

Save as a script file and run:

# RuboCop — Ruby Static Code Analyzer and Formatter

## Quick Use
```bash
gem install rubocop
cd your-ruby-project
rubocop
rubocop -a   # auto-correct safe violations
```

## Introduction
RuboCop enforces the community Ruby style guide through static analysis and automatic formatting. It catches style violations, naming issues, and code complexity problems, then auto-corrects many of them. It is the standard linter in the Ruby ecosystem.

## What RuboCop Does
- Checks Ruby source files against hundreds of configurable cops (rules)
- Auto-corrects safe violations with `-a` and all correctable violations with `-A`
- Supports department-based organization: Layout, Lint, Metrics, Naming, Style, and Security
- Integrates with editors, CI pipelines, and pre-commit hooks
- Generates TODO files for incremental adoption on legacy codebases

## Architecture Overview
RuboCop uses the parser gem to produce an AST from Ruby source files. Each cop is a class that registers on specific AST node types via a visitor pattern. The runner coordinates file discovery, cop execution, and formatter output. Auto-correction works by rewriting source ranges on the AST, with conflict resolution for overlapping corrections.

## Self-Hosting & Configuration
- Install as a gem (`gem install rubocop`) or add to your Gemfile as a development dependency
- Create a `.rubocop.yml` file to enable, disable, or configure individual cops
- Generate a `.rubocop_todo.yml` with `rubocop --auto-gen-config` to baseline existing violations
- Add department-specific extensions like `rubocop-rails`, `rubocop-rspec`, or `rubocop-performance`
- Use `inherit_from` in `.rubocop.yml` to share configurations across projects

## Key Features
- Over 450 built-in cops covering style, lint, metrics, naming, and security
- Safe and unsafe auto-correction modes for fixing violations automatically
- Extension gems for Rails, RSpec, Minitest, Performance, and more
- Caching for fast incremental analysis on unchanged files
- Multiple output formatters including JSON, HTML, and GitHub Actions annotations

## Comparison with Similar Tools
- **Standard** — a zero-configuration RuboCop wrapper with opinionated defaults; RuboCop offers full customization
- **Reek** — detects code smells like feature envy and long methods; RuboCop covers broader style and lint rules
- **Flay** — finds duplicated code; RuboCop focuses on style and correctness rather than duplication
- **Brakeman** — scans for Rails security vulnerabilities; RuboCop covers general code quality with a smaller security department

## FAQ
**Q: How do I adopt RuboCop on a large legacy codebase?**
A: Run `rubocop --auto-gen-config` to create a TODO file that disables all current violations, then enable cops incrementally.

**Q: What is the difference between `-a` and `-A`?**
A: The `-a` flag applies only safe corrections that preserve behavior. The `-A` flag also applies unsafe corrections that may change semantics.

**Q: Can I write custom cops?**
A: Yes. Create a class inheriting from `RuboCop::Cop::Base`, define `on_send` or other node callbacks, and register it via a plugin or `require` in `.rubocop.yml`.

**Q: Does RuboCop support Ruby 3.x syntax?**
A: Yes. RuboCop tracks the latest Ruby syntax through the parser gem and adds cops for new language features.

## Sources
- https://github.com/rubocop/rubocop
- https://docs.rubocop.org/

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Source: https://tokrepo.com/en/workflows/asset-2ab9eb5c
Author: Script Depot