gistfile1.txt

# Before
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  10.51s user 0.35s system 185% cpu 5.855 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  9.64s user 0.35s system 182% cpu 5.468 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  10.07s user 0.40s system 181% cpu 5.781 total

# After
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  8.70s user 0.31s system 185% cpu 4.852 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  9.50s user 0.37s system 186% cpu 5.280 total
bin/jruby --dev -e "require 'active_support/all'; p ActiveSupport"  8.66s user 0.32s system 185% cpu 4.830 total

patch.diff

diff --git a/lib/ruby/stdlib/rubygems/specification.rb b/lib/ruby/stdlib/rubygems/specification.rb
index eb89c4c..3206825 100644
--- a/lib/ruby/stdlib/rubygems/specification.rb
+++ b/lib/ruby/stdlib/rubygems/specification.rb
@@ -944,7 +944,7 @@ class Gem::Specification < Gem::BasicSpecification

   def self.find_in_unresolved path
     # TODO: do we need these?? Kill it
-    specs = unresolved_deps.values.map { |dep| dep.to_specs }.flatten
+    specs = unresolved_deps.values.flat_map { |dep| dep.to_specs }

     specs.find_all { |spec| spec.contains_requirable_file? path }
   end
@@ -954,7 +954,7 @@ class Gem::Specification < Gem::BasicSpecification
   # specs that contain the file matching +path+.

   def self.find_in_unresolved_tree path
-    specs = unresolved_deps.values.map { |dep| dep.to_specs }.flatten
+    specs = unresolved_deps.values.flat_map { |dep| dep.to_specs }

     specs.reverse_each do |spec|
       trails = []
@@ -1014,7 +1014,7 @@ class Gem::Specification < Gem::BasicSpecification
       result[spec.name][spec.platform] = spec
     end

-    result.map(&:last).map(&:values).flatten.reject { |spec|
+    result.map(&:last).flat_map(&:values).reject { |spec|
       minimum = native[spec.name]
       minimum && spec.version < minimum
     }.sort_by{ |tup| tup.name }
@@ -1625,7 +1625,7 @@ class Gem::Specification < Gem::BasicSpecification
   # Returns all specs that matches this spec's runtime dependencies.

   def dependent_specs
-    runtime_dependencies.map { |dep| dep.to_specs }.flatten
+    runtime_dependencies.flat_map { |dep| dep.to_specs }
   end