dual-boot

Claude Code Dual Boot Skill

A Claude Code skill that helps you set up and manage dual-boot environments for Ruby and Rails applications using the next_rails gem.

What Does This Skill Do?

The Dual-Boot skill helps you:

• Set up dual-boot with the next_rails gem so your app runs with two dependency sets depending on one environment variable (ie. BUNDLE_GEMFILE)
• Write version-dependent code using NextRails.next? (the correct pattern — never respond_to?)
• Configure CI to test against both dependency sets (GitHub Actions, CircleCI, Jenkins)
• Clean up dual-boot code after the upgrade is complete

While most commonly used for Rails version upgrades, dual-boot works equally well for upgrading Ruby versions or any core dependency in your Gemfile (e.g., sidekiq, devise, pg).

Why Dual-Boot?

Dual-booting is a core part of the FastRuby.io upgrade methodology:

• Quickly switch between dependency sets for debugging
• Run test suites against both versions
• Deploy backwards-compatible changes to production before the version bump
• Catch compatibility issues early in CI
• Allows you to gradually deploy versions of key dependencies (e.g. 10% of the traffic will now use the target version of Rails)

How to Use This Skill

Installation

From inside the Claude Code CLI prompt (recommended):

/plugin marketplace add ombulabs/claude-skills
/plugin install dual-boot@ombulabs-ai

From your terminal:

claude plugin marketplace add https://github.com/ombulabs/claude-skills.git
claude plugin install dual-boot@ombulabs-ai

Manual install:

git clone https://github.com/ombulabs/claude-code_dual-boot-skill.git
cp -r claude-code_dual-boot-skill/dual-boot ~/.claude/skills/

[!NOTE] This skill works standalone, but it is part of the full Rails upgrade toolkit. You may also want to install rails-load-defaults and rails-upgrade.

Basic Usage

In Claude Code, navigate to your Rails application directory and use natural language:

"Set up dual boot for my Rails app"
"Help me dual-boot Rails 7.0 and 7.1"
"Dual-boot Ruby 3.1 and 3.2"
"Set up dual boot for upgrading sidekiq"
"Configure dual-boot CI"
"Clean up dual-boot code after upgrade"

Key Principle: Use NextRails.next? (not feature detection)

When writing code that must work with two versions, always use NextRails.next?:

# spec/requests/projects_spec.rb
test_request =
  if NextRails.next?
    ActionController::TestRequest.create
  else
    ActionController::TestRequest.new
  end

Never use respond_to?, defined?, or other feature-detection patterns. They are fragile, hard to clean up, and obscure intent.

Only branch when the old API genuinely breaks on the next version. A plain deprecation warning is not a reason for a conditional — if the new API works on both versions, just use it directly.

Related Skills

• rails-upgrade skill — Comprehensive Rails upgrade assistant (uses this skill for dual-boot setup)
• rails-load-defaults skill — Incremental load_defaults updates

Contributing

We welcome contributions! Found incorrect information or have a suggestion? Open an issue.

License

This project is licensed under the MIT License. See LICENSE for details.

Sponsors

OmbuLabs.ai | Custom AI Solutions

OmbuLabs.ai is Philadelphia's AI Software Boutique. We build custom AI solutions that integrate with your existing workflows. From Claude Code skills to full AI agent systems.

FastRuby.io | Ruby Maintenance, Done Right

The Rails upgrade experts. We've been upgrading Rails applications professionally since 2017, helping companies stay current and secure.

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Questions? Open an issue or reach out to us at [email protected]