[ruby] Introduce Rubocop for Static Code Analysis

[hayat01sh1da]

1. Why (Purpose)

RuboCop has been introduced across all Ruby and Rails projects to improve reliability and maintainability by enforcing consistent coding standards based on the community-driven Ruby Style Guide. Static code analysis catches style violations, potential bugs, and performance issues early — before code reaches production — reducing review burden and keeping the codebase uniform regardless of contributor.

2. What (Procedures)

2-1. Target Projects

RuboCop was applied to 13 projects across 10 repositories.

2-1-1. Pure Ruby Projects (9 projects)

#	Repository	Sub-path	Test Framework
1	botpress-accuracy-checkers	ruby/	Minitest
2	coding-tests	ruby/	Minitest
3	file-cleaners	ruby/	Minitest
4	file-extension-converters	ruby/	Minitest
5	github-wiki-organisers	ruby/	Minitest
6	itunes-file-delimiter-replacer	ruby/	Minitest
7	json-data-sorters	ruby/	Minitest
8	pr-title-printers	ruby/	Minitest
9	template-creators	ruby/	Minitest

2-1-2. Rails Projects (4 projects)

#	Repository	Sub-path	Test Framework
1	botpress-accuracy-checkers	ruby-on-rails/	RSpec
2	tutorials	ruby-on-rails/restful-api/	RSpec
3	tutorials	ruby-on-rails/perfect-ruby-on-rails/	Minitest
4	tutorials	ruby-on-rails/e-navigator/	Minitest

2-2. Changes Made

Each repository was branched and committed with 3 semantic commits:

2-2-1. Add RuboCop Gems to Gemfile

Pure Ruby projects — Created ruby/Gemfile with:

gem 'rubocop', require: false
gem 'rubocop-minitest', require: false
gem 'rubocop-performance', require: false

Rails projects (RSpec) — Added to the :development group after brakeman:

gem 'rubocop', require: false
gem 'rubocop-performance', require: false
gem 'rubocop-rails', require: false
gem 'rubocop-rspec', require: false

Rails projects (Minitest) — Added to the :development group after brakeman:

gem 'rubocop', require: false
gem 'rubocop-minitest', require: false
gem 'rubocop-performance', require: false
gem 'rubocop-rails', require: false

2-2-2. Add .rubocop.yml

Pure Ruby projects — ruby/.rubocop.yml:

require:
  - rubocop-minitest
  - rubocop-performance

AllCops:
  TargetRubyVersion: 4.0
  NewCops: enable

Rails projects (RSpec) — .rubocop.yml:

require:
  - rubocop-performance
  - rubocop-rails
  - rubocop-rspec

AllCops:
  TargetRubyVersion: 4.0
  NewCops: enable
  Exclude:
    - 'bin/**/*'
    - 'db/schema.rb'
    - 'vendor/**/*'
    - 'node_modules/**/*'

Rails projects (Minitest) — .rubocop.yml:

require:
  - rubocop-minitest
  - rubocop-performance
  - rubocop-rails

AllCops:
  TargetRubyVersion: 4.0
  NewCops: enable
  Exclude:
    - 'bin/**/*'
    - 'db/schema.rb'
    - 'vendor/**/*'
    - 'node_modules/**/*'

2-2-3. Add RuboCop Step to CI Workflow

Pure Ruby projects — Added to .github/workflows/ruby.yml:

- name: Install Gems
  run: gem install rubocop rubocop-minitest rubocop-performance
- name: Run RuboCop
  working-directory: ./ruby
  run: rubocop

Rails projects — Added after the Run Brakeman step in each workflow:

- name: Run RuboCop
  working-directory: ./<project-path>
  run: bundle exec rubocop

2-3. Git Operations

Item	Value
Branch	ruby/introduce-rubocop-to-app
Commits per repo	3
Commit 1	Add RuboCop gems to Gemfile
Commit 2	Add .rubocop.yml
Commit 3	Add RuboCop step to CI workflow

3. How (Operation and Maintenance)

3-1. Local Development

Run RuboCop locally before pushing:

# Pure Ruby projects
cd ruby/
rubocop

# Rails projects
cd ruby-on-rails/<project>/
bundle exec rubocop

Auto-correct safe violations:

rubocop -a          # safe auto-corrections only
rubocop -A          # safe + unsafe auto-corrections (review changes carefully)

3-2. CI Enforcement

RuboCop runs automatically on every push to master and on every pull request via GitHub Actions. A failing RuboCop check will block the workflow, ensuring no style violations reach the default branch.

3-3. Updating Rules

• NewCops: enable is set so newly added cops from RuboCop upgrades are automatically enabled.

• To suppress a specific cop for a project, add an override to its .rubocop.yml:

  Style/SomeCop:
    Enabled: false

• To suppress inline:

  # rubocop:disable Style/SomeCop
  some_code
  # rubocop:enable Style/SomeCop

3-4. Keeping Dependencies Up to Date

Periodically update RuboCop and its extensions:

# Rails projects
bundle update rubocop rubocop-performance rubocop-rails rubocop-rspec
bundle update rubocop rubocop-performance rubocop-rails rubocop-minitest

# Pure Ruby projects
gem update rubocop rubocop-minitest rubocop-performance

4. Pros & Cons

4-1. Pros

#	Advantage	Description
1	Consistent code style	Enforces the community Ruby Style Guide across all projects uniformly
2	Early bug detection	Catches potential issues (e.g. unused variables, shadowed arguments) before runtime
3	Performance insights	rubocop-performance identifies inefficient patterns and suggests faster alternatives
4	Framework-aware checks	rubocop-rails / rubocop-rspec / rubocop-minitest enforce framework-specific best practices
5	Automated enforcement	CI integration prevents regressions without relying on manual review
6	Auto-correction	Many violations can be fixed automatically with rubocop -a
7	Low friction	Runs as a standalone step; does not interfere with test execution

4-2. Cons

#	Disadvantage	Mitigation
1	Initial noise	Existing code may produce many violations on first run; fix incrementally or use rubocop --auto-gen-config to generate a TODO file
2	Opinionated defaults	Some rules may conflict with project conventions; override in .rubocop.yml as needed
3	CI time increase	Adds a few seconds to each workflow run; negligible compared to test and build steps
4	Upgrade churn	NewCops: enable may introduce new violations on gem updates; review release notes before updating