[rubygems/rubygems] Fix performance regression in require

Our check for `-I` paths should not go through all activated gems.

https://github.com/rubygems/rubygems/commit/00d98eb8a3

lib/rubygems.rb

@@ -593,10 +593,20 @@ An Array (#{env.inspect}) was passed in from #{caller[3]}
     index
   end
 
+  ##
+  # The number of paths in the `$LOAD_PATH` from activated gems. Used to
+  # prioritize `-I` and `ENV['RUBYLIB`]` entries during `require`.
+
+  def self.activated_gem_paths
+    @activated_gem_paths ||= 0
+  end
+
   ##
   # Add a list of paths to the $LOAD_PATH at the proper place.
 
   def self.add_to_load_path(*paths)
+    @activated_gem_paths = activated_gem_paths + paths.size
+
     insert_index = load_path_insert_index
 
     if insert_index

lib/rubygems/core_ext/kernel_require.rb

@@ -47,7 +47,7 @@ module Kernel
         load_path_insert_index = Gem.load_path_insert_index
         break unless load_path_insert_index
 
-        $LOAD_PATH[0...load_path_insert_index].each do |lp|
+        $LOAD_PATH[0...load_path_insert_index - Gem.activated_gem_paths].each do |lp|
           safe_lp = lp.dup.tap(&Gem::UNTAINT)
           begin
             if File.symlink? safe_lp # for backward compatibility

lib/rubygems/test_case.rb

@@ -388,6 +388,7 @@ class Gem::TestCase < Minitest::Test
     Gem::Security.reset
 
     Gem.loaded_specs.clear
+    Gem.instance_variable_set(:@activated_gem_paths, 0)
     Gem.clear_default_specs
     Bundler.reset!
 

test/rubygems/test_require.rb

@@ -382,6 +382,17 @@ class TestGemRequire < Gem::TestCase
     assert_equal 0, times_called
   end
 
+  def test_second_gem_require_does_not_resolve_path_manually_before_going_through_standard_require
+    a1 = util_spec "a", "1", nil, "lib/test_gem_require_a.rb"
+    install_gem a1
+
+    assert_require "test_gem_require_a"
+
+    stub(:gem_original_require, ->(path) { assert_equal "test_gem_require_a", path }) do
+      require "test_gem_require_a"
+    end
+  end
+
   def test_realworld_default_gem
     testing_ruby_repo = !ENV["GEM_COMMAND"].nil?
     skip "this test can't work under ruby-core setup" if testing_ruby_repo || java_platform?