Gem.load_plugins loads same plugin multiple times from different Gem.path entries

[forthrin]

Posting a discussion as suggested by @tompng in ruby/rdoc#1609 (comment)

Problem

When the same gem is installed in multiple directories in Gem.path, RubyGems loads its plugin once per directory rather than once per gem.

Possible fix

RubyGems should load at most one plugin for a given gem name.

Gem.load_plugins could deduplicate plugins by gem name and select the plugin associated with the activated gem specification, or otherwise apply RubyGems’ normal gem-selection rules.

Questions for community and maintainers:

• Should deduplication be based on gem name, activated specification, or plugin path?
• Which version should provide the plugin when multiple versions are installed?
• Should duplicate plugin files generate a diagnostic?
• Are there compatibility concerns with changing plugin-loading behavior?

---

Elaboration

For example:

/opt/homebrew/lib/ruby/gems/4.0.0
/opt/homebrew/Cellar/ruby/4.0.7/lib/ruby/gems/4.0.0

Both contain RDoc, including its RubyGems plugin:

plugins/rdoc_plugin.rb

RubyGems loads both plugin files, producing warnings such as:

warning: already initialized constant RDoc::VERSION

RDoc is the only bundled gem currently shipping a RubyGems plugin, so it is the only bundled gem exposing the problem.

Pinning RDoc does not solve the underlying issue: the warning also occurs when different RDoc versions are installed, and potentially when the same version exists in multiple locations.

[wlipa]

This issue makes it difficult / impossible to manage versions of rdoc with bundler in the normal way, unless you can tolerate 10-20 lines of warnings when doing bundler operations. The workaround is lock rdoc to the version that comes with your ruby.

[forthrin]

Reposted as an issue (#9945) due to low activity in Discussions.