prefer-ruby-3-yjit

Detects repositories that use Ruby 3.2.x in CI and recommends upgrading to Ruby 3.4+ for faster YJIT.

Why This Matters

YJIT became production-ready in Ruby 3.2. Ruby 3.3’s YJIT is roughly 13% faster than 3.2’s, and Ruby 3.4 is another 5-7% faster with lower memory use. With YJIT enabled, Ruby code in CI typically runs 30-60% faster — the single largest performance improvement available without changing application code.

YJIT is opt-in at the Ruby level (--yjit or RUBY_YJIT_ENABLE=1), so it is not enabled by default even on Ruby 3.3+. Rails 7.2+ enables it by default on Ruby 3.3+ (config.yjit = true).

Detection

A finding is emitted when all of the following hold:

1. The repository Ruby version (from .ruby-version or Gemfile) is 3.2.x.
2. At least one CI job runs Ruby commands (ruby/setup-ruby, bundle install, bundle exec, rails, rake, rspec).

Not Triggered When

• Ruby 3.3+ is already in use.
• Ruby 3.1 or older (larger upgrade required).
• No Ruby CI commands are visible in workflows.

Resolution

Update .ruby-version:

- 3.2.3
+ 3.4.11

Update Gemfile if pinned:

- ruby "~> 3.2.0"
+ ruby "~> 3.4.0"

Enable YJIT in CI:

- run: bundle exec ruby --yjit rspec

Or set the environment variable:

env:
  RUBY_YJIT_ENABLE: "1"

If the app uses Rails 7.2+ on Ruby 3.3+, YJIT is already enabled by default.

Severity

• Warning — when a repository uses Ruby 3.2.x and runs Ruby CI jobs.