Use eventmachine from git master on Ruby >= 4.0

[sodabrew]

Summary

The ruby: 'head' and ruby: '4.0' CI jobs in build.yml fail during bundle install because eventmachine 1.2.7's bundled fastfilereader C++ extension calls Data_Wrap_Struct/Data_Get_Struct, both of which Ruby 4.0 removed from its headers:

rubymain.cpp:53:19: error: 'Data_Wrap_Struct' was not declared in this scope

eventmachine has had no release since 1.2.7 (2019), but its maintainer confirmed this is already fixed on master (eventmachine/eventmachine@79f05e4) — just not yet cut into a release.

Fix

Gemfile now points eventmachine at github: 'eventmachine/eventmachine' (git master) when RUBY_VERSION >= 4.0, falling back to the released 1.2.7 gem on older Rubies. spec/em/em_spec.rb already tolerates eventmachine being unavailable via a begin/rescue LoadError, so no spec changes were needed.

This is a stopgap: once eventmachine cuts a release containing the fix, the version constraint here should be updated to require that release instead of pinning to git master.

Test plan

• Installed Ruby 4.0.6 locally via mise, confirmed the CI failure reproduces with the Gemfile unchanged (eventmachine 1.2.7 fails to compile fastfilereaderext)
• With this fix, bundle install resolves eventmachine (1.3.0.dev.1) from git master and compiles fastfilereaderext.bundle/rubyeventmachine.bundle cleanly under Ruby 4.0.6
• bundle exec rspec spec/em/em_spec.rb — 6 examples, 0 failures
• Full bundle exec rspec suite — 366 examples, 1 failure (pre-existing, unrelated fork/child-process flake), 7 pending (pre-existing SSL cert path skips)
• bundle exec rubocop — clean

Ruby 4.0 and ruby-head are already present in the CI matrix in build.yml, so no workflow changes are needed — the Gemfile's version check applies automatically to those jobs.

🤖 Generated with Claude Code