[rubygems/rubygems] Revert RubyGems plugins getting loaded on Bundler.require

These changes were included when adding bundler plugin hooks for
`Bundler.require`, but they seem completely unrelated to that feature,
and have caused several issues.

https://github.com/rubygems/rubygems/commit/8d56551dcf

lib/bundler.rb

@@ -212,7 +212,6 @@ module Bundler
     #    Bundler.require(:test)   # requires second_gem
     #
     def require(*groups)
-      load_plugins
       setup(*groups).require(*groups)
     end
 
@@ -576,23 +575,6 @@ module Bundler
       @feature_flag ||= FeatureFlag.new(VERSION)
     end
 
-    def load_plugins(definition = Bundler.definition)
-      return if defined?(@load_plugins_ran)
-
-      Bundler.rubygems.load_plugins
-
-      requested_path_gems = definition.requested_specs.select {|s| s.source.is_a?(Source::Path) }
-      path_plugin_files = requested_path_gems.flat_map do |spec|
-        spec.matches_for_glob("rubygems_plugin#{Bundler.rubygems.suffix_pattern}")
-      rescue TypeError
-        error_message = "#{spec.name} #{spec.version} has an invalid gemspec"
-        raise Gem::InvalidSpecificationException, error_message
-      end
-      Bundler.rubygems.load_plugin_files(path_plugin_files)
-      Bundler.rubygems.load_env_plugins
-      @load_plugins_ran = true
-    end
-
     def reset!
       reset_paths!
       Plugin.reset!

lib/bundler/installer.rb

@@ -79,7 +79,7 @@ module Bundler
 
         if @definition.setup_domain!(options)
           ensure_specs_are_compatible!
-          Bundler.load_plugins(@definition)
+          load_plugins
         end
         install(options)
 
@@ -209,6 +209,20 @@ module Bundler
       Bundler.settings.processor_count
     end
 
+    def load_plugins
+      Gem.load_plugins
+
+      requested_path_gems = @definition.requested_specs.select {|s| s.source.is_a?(Source::Path) }
+      path_plugin_files = requested_path_gems.flat_map do |spec|
+        spec.matches_for_glob("rubygems_plugin#{Bundler.rubygems.suffix_pattern}")
+      rescue TypeError
+        error_message = "#{spec.name} #{spec.version} has an invalid gemspec"
+        raise Gem::InvalidSpecificationException, error_message
+      end
+      Gem.load_plugin_files(path_plugin_files)
+      Gem.load_env_plugins
+    end
+
     def ensure_specs_are_compatible!
       @definition.specs.each do |spec|
         unless spec.matches_current_ruby?

lib/bundler/rubygems_integration.rb

@@ -134,18 +134,6 @@ module Bundler
       loaded_gem_paths.flatten
     end
 
-    def load_plugins
-      Gem.load_plugins
-    end
-
-    def load_plugin_files(plugin_files)
-      Gem.load_plugin_files(plugin_files)
-    end
-
-    def load_env_plugins
-      Gem.load_env_plugins
-    end
-
     def ui=(obj)
       Gem::DefaultUserInteraction.ui = obj
     end

spec/bundler/runtime/require_spec.rb

@@ -431,6 +431,22 @@ RSpec.describe "Bundler.require" do
     expect(out).to eq("WIN")
   end
 
+  it "does not load plugins" do
+    install_gemfile <<-G
+      source "https://gem.repo1"
+      gem "myrack"
+    G
+
+    create_file "plugins/rubygems_plugin.rb", "puts 'FAIL'"
+
+    run <<~R, env: { "RUBYLIB" => rubylib.unshift(bundled_app("plugins").to_s).join(File::PATH_SEPARATOR) }
+      Bundler.require
+      puts "WIN"
+    R
+
+    expect(out).to eq("WIN")
+  end
+
   it "does not extract gemspecs from application cache packages" do
     gemfile <<-G
       source "https://gem.repo1"