Fix redefinition warnings when using modern RubyGems with old Bundler

Author: deivid-rodriguez

Manifest.txt

@@ -364,6 +364,7 @@ hide_lib_for_update/note.txt
 lib/rubygems.rb
 lib/rubygems/available_set.rb
 lib/rubygems/basic_specification.rb
+lib/rubygems/bundler_integration.rb
 lib/rubygems/bundler_version_finder.rb
 lib/rubygems/ci_detector.rb
 lib/rubygems/command.rb

lib/rubygems.rb

@@ -1144,7 +1144,7 @@ def self.use_gemdeps(path = nil)
 
     ENV["BUNDLE_GEMFILE"] ||= File.expand_path(path)
     require_relative "rubygems/user_interaction"
-    require "bundler"
+    require_relative "rubygems/bundler_integration"
     begin
       Gem::DefaultUserInteraction.use_ui(ui) do
         Bundler.ui.silence do

lib/rubygems/bundler_integration.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+require "bundler/version"
+
+if Bundler::VERSION > "2.6.9"
+  require "bundler"
+else
+  previous_platforms = {}
+
+  platform_const_list = ["JAVA", "MSWIN", "MSWIN64", "MINGW", "X64_MINGW_LEGACY", "X64_MINGW", "UNIVERSAL_MINGW", "WINDOWS", "X64_LINUX", "X64_LINUX_MUSL"]
+
+  platform_const_list.each do |platform|
+    previous_platforms[platform] = Gem::Platform.const_get(platform)
+    Gem::Platform.send(:remove_const, platform)
+  end
+
+  require "bundler"
+
+  platform_const_list.each do |platform|
+    Gem::Platform.send(:remove_const, platform) if Gem::Platform.const_defined?(platform)
+    Gem::Platform.const_set(platform, previous_platforms[platform])
+  end
+end