Ruby 3.1 on Rails

ruby31onrails.md

Ruby 3.1 on Rails

Actions required to use Ruby 3.1.0 with Rails

Rails 7.0.Z

• Rails 7.0.0 is not compatible with Ruby 3.1.0.

• "Rails::Engine is abstract, you cannot instantiate it directly.."

  $ bin/rails s
  Calling `DidYouMean::SPELL_CHECKERS.merge!(error_name => spell_checker)' has been deprecated. Please call `DidYouMean.correct_error(error_name, spell_checker)' instead.
  [WARNING] Could not load command "rails/commands/server/server_command". Error: Rails::Engine is abstract, you cannot instantiate it directly..
  /path/to/rails/railties/lib/rails/railtie.rb:246:in `initialize'
  /path/to/rails/railties/lib/rails/railtie.rb:184:in `new'
  /path/to/rails/railties/lib/rails/railtie.rb:184:in `instance'
  /path/to/rails/railties/lib/rails/railtie.rb:223:in `method_missing'
  /path/to/rails/activesupport/lib/active_support/descendants_tracker.rb:90:in `descendants'

• Use 7-0-stable branch until Rails 7.0.1 is released.

  gem "rails", github: "rails/rails", branch: "7-0-stable"

Rails 6.1.Z

• Use Rails 6.1.4 to support database.yml with aliases.
• If you use secrets.yml with aliases, use 6-1-stable branch.

  gem "rails", github: "rails/rails", branch: "6-1-stable"

Rails 6.0.Z

• You will likely get this error.

  Psych::BadAlias: Unknown alias: default

• Upgrade to Rails 6.1.4 or higher.
• No Psych 4 support has been backported to Rails 6.0. Use Psych 3 as a workaround.

  gem "psych", "~> 3.0"

---

Details - if you are interested

Maintenance Policy for Ruby on Rails

https://guides.rubyonrails.org/maintenance_policy.html As of Dec 25, 2021, Supporting Ruby 3.1 with Rails should not be security issues.

• Rails 7.0.Z accepts bug fixes.
• Rails 6.1.Z accepts security issues only.
• Rails 6.0.Z accepts severe security issues only.

---

Changes to support Ruby 3.1

• Add Class#descendants
• Psych 4 support
• net-smtp, net-imap, net-pop are bundled gems
• Ruby 3.1 performance optimization
• DidYouMean::SPELL_CHECKERS.merge!(error_name => spell_checker)' has been deprecated.

---

Add Class#descendants

• Rails 7.0.0 expects Ruby 3.1 has both of Class#descendants and Class#subclasses or not.

• Ruby 3.1 supports Class#subclasses only, Class#descendants has been removed on Dec 21, 2025.

• Rails 7.0.0 did not expect one of these methos removed.

• Rails 7.0.1 supports Ruby 3.1 Class#subclasses.

• Related pull requests at Ruby

  • ruby/ruby#4974
  • ruby/ruby#5070
  • ruby/ruby#5097
  • ruby/ruby#5309

• Related pull requests at Rails

  • rails/rails#43548
  • rails/rails#43722
  • rails/rails#43723
  • rails/rails#43481
  • rails/rails#43970

---

Psych 4 support

• Ruby 3.1.0 installs Psych 4.0.3 as standard library

  • Use Psych.safe_load by default

  • https://www.ruby-lang.org/en/news/2021/12/25/ruby-3-1-0-released/

    Psych 4.0 changes Psych.load as safe_load by the default. You may need to use Psych 3.3.2 for migrating to this behavior. [Bug #17866]

• Psych 4 support at Rails

  • Included to Rails 6.1.4 or later

    • rails/rails#42249
    • rails/rails#42257

  • Rails 7.0.0 or later, not released as Rails 6.1.Z yet because it has been to 6-1-stable after Rails 6.1.4 was released.

    • rails/rails#42687

---

YAML files used in Rails

• config/database.yml

  default: &default
    adapter: sqlite3
    pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
    timeout: 5000
  
  development:
    <<: *default
    database: db/development.sqlite3
  
  # Warning: The database defined as "test" will be erased and
  # re-generated from your development database when you run "rake".
  # Do not set this db to the same as development or production.
  test:
    <<: *default
    database: db/test.sqlite3
  
  production:
    <<: *default
    database: db/production.sqlite3

• config/secrets.yml (Rails 4.1+) or config/secrets.yml.enc (Rails 5.1+)
  • You will get this error run Rails 6.1 with Ruby 3.1.0

  $ bin/rails s
  => Booting Puma
  => Rails 6.1.4.4 application starting in development
  => Run `bin/rails server --help` for more startup options
  Exiting
  /home/yahonda/.rbenv/versions/3.1.0-dev/lib/ruby/3.1.0/psych/visitors/to_ruby.rb:430:in `visit_Psych_Nodes_Alias': Unknown alias: default (Psych::BadAlias)

• config/credentials.yml.enc
  • No alias supported in Rails main branch because it should not need alias support.

---

net-smtp, net-imap, net-pop are bundled gems

• If you need to use mail gem, add them explicitly in your Gemfile
• mikel/mail#1439

---

Ruby 3.1 performance optimization

• Optimize dynamic string interpolation for symbol/true/false/nil/0-9 ruby/ruby#5002 rails/rails#43772 https://bugs.ruby-lang.org/issues/13715

---

did_you_mean gem shows this deprecation at thor

• Calling DidYouMean::SPELL_CHECKERS.merge!(error_name => spell_checker)' has been deprecated. Please call DidYouMean.correct_error(error_name, spell_checker)' instead.
• rails/thor#761

---

Enjoy Ruby 3.1!