feat!: add Ruby 4.0 support, require minimum Ruby 3.4

[josecolella]

Summary

• Add Ruby 4.0 support: Ruby 4.0.1 (released January 2026) is now tested in CI and fully supported
• Raise minimum Ruby to 3.4: Drop support for Ruby 3.1 (EOL March 2025), 3.2 (EOL March 2026), and 3.3 (security-only maintenance)
• Update tooling: .ruby-version, .tool-versions, CI matrix, gemspec constraint, README version table, and Gemfile.lock all updated

Breaking Change

Minimum required Ruby version is now 3.4. Ruby 3.1, 3.2, and 3.3 are no longer supported.

• See: https://www.ruby-lang.org/en/downloads/branches/

Verification

• bundle exec rspec — all 272 tests pass on Ruby 4.0.1
• bundle exec standardrb — 49 files inspected, no offenses
• No code changes needed for Ruby 4.0 compatibility

Test plan

• CI passes on Ruby 4.0 matrix entry
• CI passes on Ruby 3.4 matrix entry
• StandardRB linter job passes

🤖 Jose's AI agent

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly upgrades the project's Ruby environment by introducing support for Ruby 4.0 and enforcing a higher minimum Ruby version of 3.4. This change ensures compatibility with future Ruby releases while streamlining the development environment by removing support for older, less maintained versions. The update also involves a comprehensive refresh of gem dependencies and development configurations to maintain stability and leverage the latest features.

Highlights

• Ruby 4.0 Support Added: The project now officially supports and is tested against Ruby 4.0.1, which is slated for release in January 2026.
• Minimum Ruby Version Raised: The minimum required Ruby version has been increased to 3.4, discontinuing support for Ruby 3.1, 3.2, and 3.3.
• Tooling and Dependencies Updated: Various development tooling configurations, CI matrix entries, gemspec constraints, and gem dependencies have been updated to align with the new Ruby version requirements.

Changelog

• .ruby-version
  • Updated the specified Ruby version from 3.4.8 to 4.0.1.
• .tool-versions
  • Updated the Ruby version for development tools from 3.4.8 to 4.0.1.
• Gemfile.lock
  • Updated numerous gem dependencies to their latest compatible versions, including ast, debug, diff-lcs, docile, io-console, irb, json, language_server-protocol, markly, parallel, parser, psych, racc, rake, rdoc, regexp_parser, reline, rexml, rubocop, rubocop-ast, rubocop-performance, simplecov-html, standard, standard-performance, stringio, and unicode-display_width.
  • Added new direct or transitive dependencies: date, erb, pp, prettyprint, prism, tsort, and unicode-emoji.
  • Added arm64-darwin-25 to the list of supported platforms.
• README.md
  • Removed Ruby 3.1.x, 3.2.x, and 3.3.x from the supported versions table.
  • Added Ruby 3.4.x and 4.0.x to the supported Ruby versions table.
• openfeature-sdk.gemspec
  • Changed the minimum required Ruby version from >= 3.1 to >= 3.4.

Ignored Files

• Ignored by pattern: .github/workflows/** (1)
  • .github/workflows/main.yml

Activity

• The pull request author has outlined verification steps, including passing bundle exec rspec and bundle exec standardrb on Ruby 4.0.1, and confirmed no code changes were needed for Ruby 4.0 compatibility.
• A test plan has been provided, focusing on CI pass status for Ruby 4.0 and 3.4 matrix entries, and StandardRB linter job success.
• No human review comments or additional activity have been recorded since the pull request was created.

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[gemini-code-assist]

Code Review

This pull request successfully updates the project to support Ruby 4.0 and raises the minimum required Ruby version to 3.4. The changes across .ruby-version, .tool-versions, Gemfile.lock, README.md, and openfeature-sdk.gemspec are consistent with the stated goals. The dependency updates in Gemfile.lock are a natural consequence of the Ruby version bump, and the documentation and gemspec reflect the new minimum Ruby version correctly. The verification steps and test plan outlined in the PR description are also appropriate for these changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.65%. Comparing base (67b9796) to head (965e413).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #217   +/-   ##
=======================================
  Coverage   99.64%   99.65%           
=======================================
  Files          26       26           
  Lines         571      578    +7     
=======================================
+ Hits          569      576    +7     
  Misses          2        2           

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