GemPathSource looks for generators within any RubyGem’s /rails_generators/_generator.rb file.

Methods
E
Instance Public methods
each()

Yield each generator within rails_generator subdirectories.

Source: show | on GitHub 

     # File railties/lib/rails_generator/lookup.rb, line 225
225:       def each
226:         generator_full_paths.each do |generator|
227:           yield Spec.new(File.basename(generator).sub(/_generator.rb$/, ''), File.dirname(generator), label)
228:         end
229:       end