Merge bundler master from upstream.

  Pick from 8dd59e3ba97eb80a599f8149f31bf40773b69dc0

84 files changed, 482 insertions, 811 deletions

diff --git a/lib/bundler.rb b/lib/bundler.rb
index f792a3bc98..d8f9462c6d 100644
--- a/lib/bundler.rb
+++ b/lib/bundler.rb
@@ -1,20 +1,20 @@
 # frozen_string_literal: true
 
-require "bundler/compatibility_guard"
+require_relative "bundler/compatibility_guard"
 
-require "bundler/vendored_fileutils"
+require_relative "bundler/vendored_fileutils"
 require "pathname"
 require "rbconfig"
 
-require "bundler/errors"
-require "bundler/environment_preserver"
-require "bundler/plugin"
-require "bundler/rubygems_ext"
-require "bundler/rubygems_integration"
-require "bundler/version"
-require "bundler/constants"
-require "bundler/current_ruby"
-require "bundler/build_metadata"
+require_relative "bundler/errors"
+require_relative "bundler/environment_preserver"
+require_relative "bundler/plugin"
+require_relative "bundler/rubygems_ext"
+require_relative "bundler/rubygems_integration"
+require_relative "bundler/version"
+require_relative "bundler/constants"
+require_relative "bundler/current_ruby"
+require_relative "bundler/build_metadata"
 
 module Bundler
   environment_preserver = EnvironmentPreserver.new(ENV, EnvironmentPreserver::BUNDLER_KEYS)
@@ -22,43 +22,43 @@ module Bundler
   ENV.replace(environment_preserver.backup)
   SUDO_MUTEX = Mutex.new
 
-  autoload :Definition,             "bundler/definition"
-  autoload :Dependency,             "bundler/dependency"
-  autoload :DepProxy,               "bundler/dep_proxy"
-  autoload :Deprecate,              "bundler/deprecate"
-  autoload :Dsl,                    "bundler/dsl"
-  autoload :EndpointSpecification,  "bundler/endpoint_specification"
-  autoload :Env,                    "bundler/env"
-  autoload :Fetcher,                "bundler/fetcher"
-  autoload :FeatureFlag,            "bundler/feature_flag"
-  autoload :GemHelper,              "bundler/gem_helper"
-  autoload :GemHelpers,             "bundler/gem_helpers"
-  autoload :GemRemoteFetcher,       "bundler/gem_remote_fetcher"
-  autoload :GemVersionPromoter,     "bundler/gem_version_promoter"
-  autoload :Graph,                  "bundler/graph"
-  autoload :Index,                  "bundler/index"
-  autoload :Injector,               "bundler/injector"
-  autoload :Installer,              "bundler/installer"
-  autoload :LazySpecification,      "bundler/lazy_specification"
-  autoload :LockfileParser,         "bundler/lockfile_parser"
-  autoload :MatchPlatform,          "bundler/match_platform"
-  autoload :ProcessLock,            "bundler/process_lock"
-  autoload :RemoteSpecification,    "bundler/remote_specification"
-  autoload :Resolver,               "bundler/resolver"
-  autoload :Retry,                  "bundler/retry"
-  autoload :RubyDsl,                "bundler/ruby_dsl"
-  autoload :RubyGemsGemInstaller,   "bundler/rubygems_gem_installer"
-  autoload :RubyVersion,            "bundler/ruby_version"
-  autoload :Runtime,                "bundler/runtime"
-  autoload :Settings,               "bundler/settings"
-  autoload :SharedHelpers,          "bundler/shared_helpers"
-  autoload :Source,                 "bundler/source"
-  autoload :SourceList,             "bundler/source_list"
-  autoload :SpecSet,                "bundler/spec_set"
-  autoload :StubSpecification,      "bundler/stub_specification"
-  autoload :UI,                     "bundler/ui"
-  autoload :URICredentialsFilter,   "bundler/uri_credentials_filter"
-  autoload :VersionRanges,          "bundler/version_ranges"
+  autoload :Definition,             File.expand_path("bundler/definition", __dir__)
+  autoload :Dependency,             File.expand_path("bundler/dependency", __dir__)
+  autoload :DepProxy,               File.expand_path("bundler/dep_proxy", __dir__)
+  autoload :Deprecate,              File.expand_path("bundler/deprecate", __dir__)
+  autoload :Dsl,                    File.expand_path("bundler/dsl", __dir__)
+  autoload :EndpointSpecification,  File.expand_path("bundler/endpoint_specification", __dir__)
+  autoload :Env,                    File.expand_path("bundler/env", __dir__)
+  autoload :Fetcher,                File.expand_path("bundler/fetcher", __dir__)
+  autoload :FeatureFlag,            File.expand_path("bundler/feature_flag", __dir__)
+  autoload :GemHelper,              File.expand_path("bundler/gem_helper", __dir__)
+  autoload :GemHelpers,             File.expand_path("bundler/gem_helpers", __dir__)
+  autoload :GemRemoteFetcher,       File.expand_path("bundler/gem_remote_fetcher", __dir__)
+  autoload :GemVersionPromoter,     File.expand_path("bundler/gem_version_promoter", __dir__)
+  autoload :Graph,                  File.expand_path("bundler/graph", __dir__)
+  autoload :Index,                  File.expand_path("bundler/index", __dir__)
+  autoload :Injector,               File.expand_path("bundler/injector", __dir__)
+  autoload :Installer,              File.expand_path("bundler/installer", __dir__)
+  autoload :LazySpecification,      File.expand_path("bundler/lazy_specification", __dir__)
+  autoload :LockfileParser,         File.expand_path("bundler/lockfile_parser", __dir__)
+  autoload :MatchPlatform,          File.expand_path("bundler/match_platform", __dir__)
+  autoload :ProcessLock,            File.expand_path("bundler/process_lock", __dir__)
+  autoload :RemoteSpecification,    File.expand_path("bundler/remote_specification", __dir__)
+  autoload :Resolver,               File.expand_path("bundler/resolver", __dir__)
+  autoload :Retry,                  File.expand_path("bundler/retry", __dir__)
+  autoload :RubyDsl,                File.expand_path("bundler/ruby_dsl", __dir__)
+  autoload :RubyGemsGemInstaller,   File.expand_path("bundler/rubygems_gem_installer", __dir__)
+  autoload :RubyVersion,            File.expand_path("bundler/ruby_version", __dir__)
+  autoload :Runtime,                File.expand_path("bundler/runtime", __dir__)
+  autoload :Settings,               File.expand_path("bundler/settings", __dir__)
+  autoload :SharedHelpers,          File.expand_path("bundler/shared_helpers", __dir__)
+  autoload :Source,                 File.expand_path("bundler/source", __dir__)
+  autoload :SourceList,             File.expand_path("bundler/source_list", __dir__)
+  autoload :SpecSet,                File.expand_path("bundler/spec_set", __dir__)
+  autoload :StubSpecification,      File.expand_path("bundler/stub_specification", __dir__)
+  autoload :UI,                     File.expand_path("bundler/ui", __dir__)
+  autoload :URICredentialsFilter,   File.expand_path("bundler/uri_credentials_filter", __dir__)
+  autoload :VersionRanges,          File.expand_path("bundler/version_ranges", __dir__)
 
   class << self
     def configure
@@ -197,19 +197,19 @@ module Bundler
     def user_bundle_path(dir = "home")
       env_var, fallback = case dir
                           when "home"
-                            ["BUNDLE_USER_HOME", Pathname.new(user_home).join(".bundle")]
+                            ["BUNDLE_USER_HOME", proc { Pathname.new(user_home).join(".bundle") }]
                           when "cache"
-                            ["BUNDLE_USER_CACHE", user_bundle_path.join("cache")]
+                            ["BUNDLE_USER_CACHE", proc { user_bundle_path.join("cache") }]
                           when "config"
-                            ["BUNDLE_USER_CONFIG", user_bundle_path.join("config")]
+                            ["BUNDLE_USER_CONFIG", proc { user_bundle_path.join("config") }]
                           when "plugin"
-                            ["BUNDLE_USER_PLUGIN", user_bundle_path.join("plugin")]
+                            ["BUNDLE_USER_PLUGIN", proc { user_bundle_path.join("plugin") }]
                           else
                             raise BundlerError, "Unknown user path requested: #{dir}"
       end
       # `fallback` will already be a Pathname, but Pathname.new() is
       # idempotent so it's OK
-      Pathname.new(ENV.fetch(env_var, fallback))
+      Pathname.new(ENV.fetch(env_var, &fallback))
     end
 
     def user_cache
diff --git a/lib/bundler/bundler.gemspec b/lib/bundler/bundler.gemspec
index d8abb2b16f..6ce881e51a 100644
--- a/lib/bundler/bundler.gemspec
+++ b/lib/bundler/bundler.gemspec
@@ -1,10 +1,10 @@
 # frozen_string_literal: true
 
 begin
-  require File.expand_path("../lib/bundler/version", __FILE__)
+  require_relative "lib/bundler/version"
 rescue LoadError
   # for Ruby core repository
-  require File.expand_path("../version", __FILE__)
+  require_relative "version"
 end
 
 Gem::Specification.new do |s|
@@ -31,27 +31,23 @@ Gem::Specification.new do |s|
     }
   end
 
-  if s.version >= Gem::Version.new("2.a".dup)
-    s.required_ruby_version     = ">= 2.3.0"
-    s.required_rubygems_version = ">= 2.5.0"
-  else
-    s.required_ruby_version     = ">= 1.8.7"
-    s.required_rubygems_version = ">= 1.3.6"
-  end
+  s.required_ruby_version     = ">= 2.3.0"
+  s.required_rubygems_version = ">= 2.5.0"
 
   s.add_development_dependency "automatiek", "~> 0.1.0"
   s.add_development_dependency "rake",       "~> 12.0"
   s.add_development_dependency "ronn",       "~> 0.7.3"
   s.add_development_dependency "rspec",      "~> 3.6"
-  s.add_development_dependency "rubocop",    "= 0.65.0"
+  s.add_development_dependency "rubocop",    "= 0.68.1"
+  s.add_development_dependency "rubocop-performance", "~> 1.1"
 
-  # s.files = Dir.glob("{lib,exe}/**/*", File::FNM_DOTMATCH).reject {|f| File.directory?(f) }
+  s.files = Dir.glob("{lib,exe}/**/*", File::FNM_DOTMATCH).reject {|f| File.directory?(f) }
 
   # we don't check in man pages, but we need to ship them because
   # we use them to generate the long-form help for each command.
-  # s.files += Dir.glob("man/**/*")
+  s.files += Dir.glob("man/**/*")
   # Include the CHANGELOG.md, LICENSE.md, README.md manually
-  # s.files += %w[CHANGELOG.md LICENSE.md README.md]
+  s.files += %w[CHANGELOG.md LICENSE.md README.md]
   # include the gemspec itself because warbler breaks w/o it
   s.files += %w[bundler.gemspec]
 
diff --git a/lib/bundler/capistrano.rb b/lib/bundler/capistrano.rb
index 1b7145b72b..573df95043 100644
--- a/lib/bundler/capistrano.rb
+++ b/lib/bundler/capistrano.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/shared_helpers"
+require_relative "shared_helpers"
 Bundler::SharedHelpers.major_deprecation 2,
   "The Bundler task for Capistrano. Please use http://github.com/capistrano/bundler"
 
@@ -8,7 +8,7 @@ Bundler::SharedHelpers.major_deprecation 2,
 #
 # Add "require 'bundler/capistrano'" in your Capistrano deploy.rb, and
 # Bundler will be activated after each new deployment.
-require "bundler/deployment"
+require_relative "deployment"
 require "capistrano/version"
 
 if defined?(Capistrano::Version) && Gem::Version.new(Capistrano::Version).release >= Gem::Version.new("3.0")
diff --git a/lib/bundler/cli.rb b/lib/bundler/cli.rb
index 4e3735847e..dd733a22ed 100644
--- a/lib/bundler/cli.rb
+++ b/lib/bundler/cli.rb
@@ -1,11 +1,10 @@
 # frozen_string_literal: true
 
-require "bundler"
-require "bundler/vendored_thor"
+require_relative "vendored_thor"
 
 module Bundler
   class CLI < Thor
-    require "bundler/cli/common"
+    require_relative "cli/common"
 
     package_name "Bundler"
 
@@ -139,7 +138,7 @@ module Bundler
     D
     method_option "gemspec", :type => :string, :banner => "Use the specified .gemspec to create the Gemfile"
     def init
-      require "bundler/cli/init"
+      require_relative "cli/init"
       Init.new(options.dup).run
     end
 
@@ -157,7 +156,7 @@ module Bundler
       "Specify a different path than the system default ($BUNDLE_PATH or $GEM_HOME).#{" Bundler will remember this value for future installs on this machine" unless Bundler.feature_flag.forget_cli_options?}"
     map "c" => "check"
     def check
-      require "bundler/cli/check"
+      require_relative "cli/check"
       Check.new(options).run
     end
 
@@ -168,7 +167,7 @@ module Bundler
     method_option "install", :type => :boolean, :banner =>
       "Runs 'bundle install' after removing the gems from the Gemfile"
     def remove(*gems)
-      require "bundler/cli/remove"
+      require_relative "cli/remove"
       Remove.new(gems, options).run
     end
 
@@ -230,7 +229,7 @@ module Bundler
         remembered_flag_deprecation(option)
       end
 
-      require "bundler/cli/install"
+      require_relative "cli/install"
       Bundler.settings.temporary(:no_install => false) do
         Install.new(options.dup).run
       end
@@ -276,7 +275,7 @@ module Bundler
       "Update everything."
     def update(*gems)
       SharedHelpers.major_deprecation(2, "The `--force` option has been renamed to `--redownload`") if ARGV.include?("--force")
-      require "bundler/cli/update"
+      require_relative "cli/update"
       Bundler.settings.temporary(:no_install => false) do
         Update.new(options, gems).run
       end
@@ -312,7 +311,7 @@ module Bundler
             Bundler::SharedHelpers.major_deprecation(2, "use `bundle #{new_argv}` instead of `bundle #{old_argv}`")
           end
         end
-        require "bundler/cli/show"
+        require_relative "cli/show"
         Show.new(options, gem_name).run
       end
     end
@@ -323,7 +322,7 @@ module Bundler
     method_option "without-group", :type => :string, :banner => "print all gems except from a group"
     method_option "paths", :type => :boolean, :banner => "print the path to each gem in the bundle"
     def list
-      require "bundler/cli/list"
+      require_relative "cli/list"
       List.new(options).run
     end
 
@@ -332,7 +331,7 @@ module Bundler
     desc "info GEM [OPTIONS]", "Show information for the given gem"
     method_option "path", :type => :boolean, :banner => "Print full path to gem"
     def info(gem_name)
-      require "bundler/cli/info"
+      require_relative "cli/info"
       Info.new(options, gem_name).run
     end
 
@@ -353,7 +352,7 @@ module Bundler
     method_option "all", :type => :boolean, :banner =>
       "Install binstubs for all gems"
     def binstubs(*gems)
-      require "bundler/cli/binstubs"
+      require_relative "cli/binstubs"
       Binstubs.new(options, gems).run
     end
 
@@ -364,12 +363,14 @@ module Bundler
     method_option "version", :aliases => "-v", :type => :string
     method_option "group", :aliases => "-g", :type => :string
     method_option "source", :aliases => "-s", :type => :string
+    method_option "git", :type => :string
+    method_option "branch", :type => :string
     method_option "skip-install", :type => :boolean, :banner =>
       "Adds gem to the Gemfile but does not install it"
     method_option "optimistic", :type => :boolean, :banner => "Adds optimistic declaration of version to gem"
     method_option "strict", :type => :boolean, :banner => "Adds strict declaration of version to gem"
     def add(*gems)
-      require "bundler/cli/add"
+      require_relative "cli/add"
       Add.new(options.dup, gems).run
     end
 
@@ -405,7 +406,7 @@ module Bundler
     method_option "only-explicit", :type => :boolean, :banner =>
       "Only list gems specified in your Gemfile, not their dependencies"
     def outdated(*gems)
-      require "bundler/cli/outdated"
+      require_relative "cli/outdated"
       Outdated.new(options, gems).run
     end
 
@@ -420,7 +421,7 @@ module Bundler
       method_option "all-platforms", :type => :boolean, :banner => "Include gems for all platforms present in the lockfile, not only the current one"
       method_option "no-prune", :type => :boolean, :banner => "Don't remove stale gems from the cache."
       def cache
-        require "bundler/cli/cache"
+        require_relative "cli/cache"
         Cache.new(options).run
       end
     end
@@ -448,7 +449,7 @@ module Bundler
       bundle without having to download any additional gems.
     D
     def package
-      require "bundler/cli/package"
+      require_relative "cli/package"
       Package.new(options).run
     end
     map %w[pack] => :package
@@ -463,7 +464,7 @@ module Bundler
     D
     map "e" => "exec"
     def exec(*args)
-      require "bundler/cli/exec"
+      require_relative "cli/exec"
       Exec.new(options, args).run
     end
 
@@ -479,19 +480,19 @@ module Bundler
       will show the current value, as well as any superceded values and
       where they were specified.
     D
-    require "bundler/cli/config"
+    require_relative "cli/config"
     subcommand "config", Config
 
     desc "open GEM", "Opens the source directory of the given bundled gem"
     def open(name)
-      require "bundler/cli/open"
+      require_relative "cli/open"
       Open.new(options, name).run
     end
 
     unless Bundler.feature_flag.bundler_3_mode?
       desc "console [GROUP]", "Opens an IRB session with the bundle pre-loaded"
       def console(group = nil)
-        require "bundler/cli/console"
+        require_relative "cli/console"
         Console.new(options, group).run
       end
     end
@@ -539,7 +540,7 @@ module Bundler
       method_option :without, :type => :array, :default => [], :aliases => "-W", :banner => "GROUP[ GROUP...]", :desc => "Exclude gems that are part of the specified named group."
       def viz
         SharedHelpers.major_deprecation 2, "The `viz` command has been moved to the `bundle-viz` gem, see https://github.com/bundler/bundler-viz"
-        require "bundler/cli/viz"
+        require_relative "cli/viz"
         Viz.new(options.dup).run
       end
     end
@@ -563,7 +564,7 @@ module Bundler
       def gem_command.run(instance, args = [])
         arity = 1 # name
 
-        require "bundler/cli/gem"
+        require_relative "cli/gem"
         cmd_args = args + [instance]
         cmd_args.unshift(instance.options)
 
@@ -591,7 +592,7 @@ module Bundler
     method_option "force", :type => :boolean, :default => false, :banner =>
       "Forces clean even if --path is not set"
     def clean
-      require "bundler/cli/clean"
+      require_relative "cli/clean"
       Clean.new(options.dup).run
     end
 
@@ -599,7 +600,7 @@ module Bundler
     method_option "ruby", :type => :boolean, :default => false, :banner =>
       "only display ruby related platform information"
     def platform
-      require "bundler/cli/platform"
+      require_relative "cli/platform"
       Platform.new(options).run
     end
 
@@ -610,7 +611,7 @@ module Bundler
      "Install gem into a bundler group"
     def inject(name, version)
       SharedHelpers.major_deprecation 2, "The `inject` command has been replaced by the `add` command"
-      require "bundler/cli/inject"
+      require_relative "cli/inject"
       Inject.new(options.dup, name, version).run
     end
 
@@ -642,7 +643,7 @@ module Bundler
     method_option "conservative", :type => :boolean, :banner =>
       "If updating, use bundle install conservative update behavior and do not allow shared dependencies to be updated"
     def lock
-      require "bundler/cli/lock"
+      require_relative "cli/lock"
       Lock.new(options).run
     end
 
@@ -662,13 +663,13 @@ module Bundler
     method_option "quiet", :type => :boolean, :banner =>
         "Only output warnings and errors."
     def doctor
-      require "bundler/cli/doctor"
+      require_relative "cli/doctor"
       Doctor.new(options).run
     end
 
     desc "issue", "Learn how to report an issue in Bundler"
     def issue
-      require "bundler/cli/issue"
+      require_relative "cli/issue"
       Issue.new.run
     end
 
@@ -679,12 +680,12 @@ module Bundler
       checkout --force`.
     D
     def pristine(*gems)
-      require "bundler/cli/pristine"
+      require_relative "cli/pristine"
       Pristine.new(gems).run
     end
 
     if Bundler.feature_flag.plugins?
-      require "bundler/cli/plugin"
+      require_relative "cli/plugin"
       desc "plugin", "Manage the bundler plugins"
       subcommand "plugin", Plugin
     end
diff --git a/lib/bundler/cli/add.rb b/lib/bundler/cli/add.rb
index 9709e71be0..7c6235f17c 100644
--- a/lib/bundler/cli/add.rb
+++ b/lib/bundler/cli/add.rb
@@ -2,34 +2,45 @@
 
 module Bundler
   class CLI::Add
+    attr_reader :gems, :options, :version
+
     def initialize(options, gems)
       @gems = gems
       @options = options
-      @options[:group] = @options[:group].split(",").map(&:strip) if !@options[:group].nil? && !@options[:group].empty?
+      @options[:group] = options[:group].split(",").map(&:strip) unless options[:group].nil?
+      @version = options[:version].split(",").map(&:strip) unless options[:version].nil?
     end
 
     def run
-      raise InvalidOption, "You can not specify `--strict` and `--optimistic` at the same time." if @options[:strict] && @options[:optimistic]
-
-      # raise error when no gems are specified
-      raise InvalidOption, "Please specify gems to add." if @gems.empty?
+      validate_options!
+      inject_dependencies
+      perform_bundle_install unless options["skip-install"]
+    end
 
-      version = @options[:version].nil? ? nil : @options[:version].split(",").map(&:strip)
+  private
 
-      unless version.nil?
-        version.each do |v|
-          raise InvalidOption, "Invalid gem requirement pattern '#{v}'" unless Gem::Requirement::PATTERN =~ v.to_s
-        end
-      end
+    def perform_bundle_install
+      Installer.install(Bundler.root, Bundler.definition)
+    end
 
-      dependencies = @gems.map {|g| Bundler::Dependency.new(g, version, @options) }
+    def inject_dependencies
+      dependencies = gems.map {|g| Bundler::Dependency.new(g, version, options) }
 
       Injector.inject(dependencies,
-        :conservative_versioning => @options[:version].nil?, # Perform conservative versioning only when version is not specified
-        :optimistic => @options[:optimistic],
-        :strict => @options[:strict])
+        :conservative_versioning => options[:version].nil?, # Perform conservative versioning only when version is not specified
+        :optimistic => options[:optimistic],
+        :strict => options[:strict])
+    end
+
+    def validate_options!
+      raise InvalidOption, "You can not specify `--strict` and `--optimistic` at the same time." if options[:strict] && options[:optimistic]
 
-      Installer.install(Bundler.root, Bundler.definition) unless @options["skip-install"]
+      # raise error when no gems are specified
+      raise InvalidOption, "Please specify gems to add." if gems.empty?
+
+      version.to_a.each do |v|
+        raise InvalidOption, "Invalid gem requirement pattern '#{v}'" unless Gem::Requirement::PATTERN =~ v.to_s
+      end
     end
   end
 end
diff --git a/lib/bundler/cli/common.rb b/lib/bundler/cli/common.rb
index 9ea52baa6b..cec7bcadb4 100644
--- a/lib/bundler/cli/common.rb
+++ b/lib/bundler/cli/common.rb
@@ -14,17 +14,18 @@ module Bundler
       Bundler.ui.info msg
     end
 
-    def self.output_without_groups_message
+    def self.output_without_groups_message(command)
       return if Bundler.settings[:without].empty?
-      Bundler.ui.confirm without_groups_message
+      Bundler.ui.confirm without_groups_message(command)
     end
 
-    def self.without_groups_message
+    def self.without_groups_message(command)
+      command_in_past_tense = command == :install ? "installed" : "updated"
       groups = Bundler.settings[:without]
       group_list = [groups[0...-1].join(", "), groups[-1..-1]].
         reject {|s| s.to_s.empty? }.join(" and ")
       group_str = groups.size == 1 ? "group" : "groups"
-      "Gems in the #{group_str} #{group_list} were not installed."
+      "Gems in the #{group_str} #{group_list} were not #{command_in_past_tense}."
     end
 
     def self.select_spec(name, regex_match = nil)
@@ -59,7 +60,7 @@ module Bundler
     end
 
     def self.gem_not_found_message(missing_gem_name, alternatives)
-      require "bundler/similarity_detector"
+      require_relative "../similarity_detector"
       message = "Could not find gem '#{missing_gem_name}'."
       alternate_names = alternatives.map {|a| a.respond_to?(:name) ? a.name : a }
       suggestions = SimilarityDetector.new(alternate_names).similar_word_list(missing_gem_name)
diff --git a/lib/bundler/cli/doctor.rb b/lib/bundler/cli/doctor.rb
index 6d038937c0..1b3913a300 100644
--- a/lib/bundler/cli/doctor.rb
+++ b/lib/bundler/cli/doctor.rb
@@ -56,7 +56,7 @@ module Bundler
     end
 
     def check!
-      require "bundler/cli/check"
+      require_relative "check"
       Bundler::CLI::Check.new({}).run
     end
 
diff --git a/lib/bundler/cli/exec.rb b/lib/bundler/cli/exec.rb
index c29d632307..5dcf4a01ef 100644
--- a/lib/bundler/cli/exec.rb
+++ b/lib/bundler/cli/exec.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/current_ruby"
+require_relative "../current_ruby"
 
 module Bundler
   class CLI::Exec
@@ -27,12 +27,7 @@ module Bundler
         if !Bundler.settings[:disable_exec_load] && ruby_shebang?(bin_path)
           return kernel_load(bin_path, *args)
         end
-        # First, try to exec directly to something in PATH
-        if Bundler.current_ruby.jruby_18?
-          kernel_exec(bin_path, *args)
-        else
-          kernel_exec([bin_path, cmd], *args)
-        end
+        kernel_exec(bin_path, *args)
       else
         # exec using the given command
         kernel_exec(cmd, *args)
@@ -69,7 +64,7 @@ module Bundler
       Process.setproctitle(process_title(file, args)) if Process.respond_to?(:setproctitle)
       ui = Bundler.ui
       Bundler.ui = nil
-      require "bundler/setup"
+      require_relative "../setup"
       TRAPPED_SIGNALS.each {|s| trap(s, "DEFAULT") }
       Kernel.load(file)
     rescue SystemExit, SignalException
diff --git a/lib/bundler/cli/install.rb b/lib/bundler/cli/install.rb
index 03edc7fbd2..d823fb632f 100644
--- a/lib/bundler/cli/install.rb
+++ b/lib/bundler/cli/install.rb
@@ -66,7 +66,7 @@ module Bundler
       Bundler.load.cache if Bundler.app_cache.exist? && !options["no-cache"] && !Bundler.frozen_bundle?
 
       Bundler.ui.confirm "Bundle complete! #{dependencies_count_for(definition)}, #{gems_installed_for(definition)}."
-      Bundler::CLI::Common.output_without_groups_message
+      Bundler::CLI::Common.output_without_groups_message(:install)
 
       if Bundler.use_system_gems?
         Bundler.ui.confirm "Use `bundle info [gemname]` to see where a bundled gem is installed."
@@ -80,7 +80,7 @@ module Bundler
       warn_ambiguous_gems
 
       if CLI::Common.clean_after_install?
-        require "bundler/cli/clean"
+        require_relative "clean"
         Bundler::CLI::Clean.new(options).run
       end
     rescue GemNotFound, VersionConflict => e
diff --git a/lib/bundler/cli/issue.rb b/lib/bundler/cli/issue.rb
index bba1619340..054ce76315 100644
--- a/lib/bundler/cli/issue.rb
+++ b/lib/bundler/cli/issue.rb
@@ -33,7 +33,7 @@ module Bundler
     end
 
     def doctor
-      require "bundler/cli/doctor"
+      require_relative "doctor"
       Bundler::CLI::Doctor.new({}).run
     end
   end
diff --git a/lib/bundler/cli/outdated.rb b/lib/bundler/cli/outdated.rb
index 3a0521de1e..857caf0a03 100644
--- a/lib/bundler/cli/outdated.rb
+++ b/lib/bundler/cli/outdated.rb
@@ -133,7 +133,7 @@ module Bundler
 
             unless options[:parseable]
               if groups
-                Bundler.ui.info "===== Group #{groups} ====="
+                Bundler.ui.info "===== #{groups_text("Group", groups)} ====="
               else
                 Bundler.ui.info "===== Without group ====="
               end
@@ -167,6 +167,10 @@ module Bundler
 
   private
 
+    def groups_text(group_text, groups)
+      "#{group_text}#{groups.split(",").size > 1 ? "s" : ""} \"#{groups}\""
+    end
+
     def retrieve_active_spec(strict, definition, current_spec)
       if strict
         active_spec = definition.find_resolved_spec(current_spec)
@@ -212,7 +216,7 @@ module Bundler
       elsif options_include_groups || !groups
         "  * #{spec_outdated_info}"
       else
-        "  * #{spec_outdated_info} in groups \"#{groups}\""
+        "  * #{spec_outdated_info} in #{groups_text("group", groups)}"
       end
 
       Bundler.ui.info output_message.rstrip
diff --git a/lib/bundler/cli/package.rb b/lib/bundler/cli/package.rb
index cd01ce422e..120a3fdcf3 100644
--- a/lib/bundler/cli/package.rb
+++ b/lib/bundler/cli/package.rb
@@ -25,7 +25,7 @@ module Bundler
   private
 
     def install
-      require "bundler/cli/install"
+      require_relative "install"
       options = self.options.dup
       if Bundler.settings[:cache_all_platforms]
         options["local"] = false
diff --git a/lib/bundler/cli/plugin.rb b/lib/bundler/cli/plugin.rb
index b5dd5b6d4b..1155c4ec9b 100644
--- a/lib/bundler/cli/plugin.rb
+++ b/lib/bundler/cli/plugin.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/vendored_thor"
+require_relative "../vendored_thor"
 module Bundler
   class CLI::Plugin < Thor
     desc "install PLUGINS", "Install the plugin from the source"
diff --git a/lib/bundler/cli/update.rb b/lib/bundler/cli/update.rb
index b088853768..afd386bd54 100644
--- a/lib/bundler/cli/update.rb
+++ b/lib/bundler/cli/update.rb
@@ -58,24 +58,44 @@ module Bundler
       Bundler.settings.set_command_option_if_given :jobs, opts["jobs"]
 
       Bundler.definition.validate_runtime!
+
+      if locked_gems = Bundler.definition.locked_gems
+        previous_locked_info = locked_gems.specs.reduce({}) do |h, s|
+          h[s.name] = { :spec => s, :version => s.version, :source => s.source.to_s }
+          h
+        end
+      end
+
       installer = Installer.install Bundler.root, Bundler.definition, opts
       Bundler.load.cache if Bundler.app_cache.exist?
 
       if CLI::Common.clean_after_install?
-        require "bundler/cli/clean"
+        require_relative "clean"
         Bundler::CLI::Clean.new(options).run
       end
 
-      if locked_gems = Bundler.definition.locked_gems
+      if locked_gems
         gems.each do |name|
-          locked_version = locked_gems.specs.find {|s| s.name == name }
-          locked_version &&= locked_version.version
-          next unless locked_version
-          new_version = Bundler.definition.specs[name].first
-          new_version &&= new_version.version
-          if !new_version
-            Bundler.ui.warn "Bundler attempted to update #{name} but it was removed from the bundle"
-          elsif new_version < locked_version
+          locked_info = previous_locked_info[name]
+          next unless locked_info
+
+          locked_spec = locked_info[:spec]
+          new_spec = Bundler.definition.specs[name].first
+          unless new_spec
+            if Bundler.rubygems.platforms.none? {|p| locked_spec.match_platform(p) }
+              Bundler.ui.warn "Bundler attempted to update #{name} but it was not considered because it is for a different platform from the current one"
+            end
+
+            next
+          end
+
+          locked_source = locked_info[:source]
+          new_source = new_spec.source.to_s
+          next if locked_source != new_source
+
+          new_version = new_spec.version
+          locked_version = locked_info[:version]
+          if new_version < locked_version
             Bundler.ui.warn "Note: #{name} version regressed from #{locked_version} to #{new_version}"
           elsif new_version == locked_version
             Bundler.ui.warn "Bundler attempted to update #{name} but its version stayed the same"
@@ -84,7 +104,7 @@ module Bundler
       end
 
       Bundler.ui.confirm "Bundle updated!"
-      Bundler::CLI::Common.output_without_groups_message
+      Bundler::CLI::Common.output_without_groups_message(:update)
       Bundler::CLI::Common.output_post_install_messages installer.post_install_messages
     end
   end
diff --git a/lib/bundler/compact_index_client.rb b/lib/bundler/compact_index_client.rb
index 2f713041c8..a5120dbba4 100644
--- a/lib/bundler/compact_index_client.rb
+++ b/lib/bundler/compact_index_client.rb
@@ -13,8 +13,8 @@ module Bundler
 
     class Error < StandardError; end
 
-    require "bundler/compact_index_client/cache"
-    require "bundler/compact_index_client/updater"
+    require_relative "compact_index_client/cache"
+    require_relative "compact_index_client/updater"
 
     attr_reader :directory
 
diff --git a/lib/bundler/compact_index_client/updater.rb b/lib/bundler/compact_index_client/updater.rb
index d77285072c..40232019bc 100644
--- a/lib/bundler/compact_index_client/updater.rb
+++ b/lib/bundler/compact_index_client/updater.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/vendored_fileutils"
+require_relative "../vendored_fileutils"
 require "stringio"
 require "zlib"
 
diff --git a/lib/bundler/compatibility_guard.rb b/lib/bundler/compatibility_guard.rb
index 958116ce55..eaff1a10d4 100644
--- a/lib/bundler/compatibility_guard.rb
+++ b/lib/bundler/compatibility_guard.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: false
 
-require "bundler/version"
+require_relative "version"
 
 if Bundler::VERSION.split(".").first.to_i >= 2
   if Gem::Version.new(Object::RUBY_VERSION.dup) < Gem::Version.new("2.3")
diff --git a/lib/bundler/definition.rb b/lib/bundler/definition.rb
index f9daae067c..76950ff96a 100644
--- a/lib/bundler/definition.rb
+++ b/lib/bundler/definition.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/lockfile_parser"
+require_relative "lockfile_parser"
 require "set"
 
 module Bundler
@@ -385,7 +385,7 @@ module Bundler
     end
 
     def to_lock
-      require "bundler/lockfile_generator"
+      require_relative "lockfile_generator"
       LockfileGenerator.generate(self)
     end
 
@@ -782,7 +782,7 @@ module Bundler
 
         # Path sources have special logic
         if s.source.instance_of?(Source::Path) || s.source.instance_of?(Source::Gemspec)
-          other_sources_specs = begin
+          new_specs = begin
             s.source.specs
           rescue PathError, GitError
             # if we won't need the source (according to the lockfile),
@@ -794,16 +794,18 @@ module Bundler
             raise
           end
 
-          other = other_sources_specs[s].first
+          new_spec = new_specs[s].first
 
           # If the spec is no longer in the path source, unlock it. This
           # commonly happens if the version changed in the gemspec
-          next unless other
+          next unless new_spec
 
-          deps2 = other.dependencies.select {|d| d.type != :development }
-          runtime_dependencies = s.dependencies.select {|d| d.type != :development }
-          # If the dependencies of the path source have changed, unlock it
-          next unless runtime_dependencies.sort == deps2.sort
+          new_runtime_deps = new_spec.dependencies.select {|d| d.type != :development }
+          old_runtime_deps = s.dependencies.select {|d| d.type != :development }
+          # If the dependencies of the path source have changed and locked spec can't satisfy new dependencies, unlock it
+          next unless new_runtime_deps.sort == old_runtime_deps.sort || new_runtime_deps.all? {|d| satisfies_locked_spec?(d) }
+
+          s.dependencies.replace(new_spec.dependencies)
         end
 
         converged << s
diff --git a/lib/bundler/dependency.rb b/lib/bundler/dependency.rb
index 8840ad6a9c..0d588bc892 100644
--- a/lib/bundler/dependency.rb
+++ b/lib/bundler/dependency.rb
@@ -1,13 +1,13 @@
 # frozen_string_literal: true
 
 require "rubygems/dependency"
-require "bundler/shared_helpers"
-require "bundler/rubygems_ext"
+require_relative "shared_helpers"
+require_relative "rubygems_ext"
 
 module Bundler
   class Dependency < Gem::Dependency
     attr_reader :autorequire
-    attr_reader :groups, :platforms, :gemfile
+    attr_reader :groups, :platforms, :gemfile, :git, :branch
 
     PLATFORM_MAP = {
       :ruby     => Gem::Platform::RUBY,
@@ -84,6 +84,8 @@ module Bundler
       @autorequire    = nil
       @groups         = Array(options["group"] || :default).map(&:to_sym)
       @source         = options["source"]
+      @git            = options["git"]
+      @branch         = options["branch"]
       @platforms      = Array(options["platforms"])
       @env            = options["env"]
       @should_include = options.fetch("should_include", true)
diff --git a/lib/bundler/deployment.rb b/lib/bundler/deployment.rb
index 291e158ca0..b432ae6ae1 100644
--- a/lib/bundler/deployment.rb
+++ b/lib/bundler/deployment.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/shared_helpers"
+require_relative "shared_helpers"
 Bundler::SharedHelpers.major_deprecation 2, "Bundler no longer integrates with " \
   "Capistrano, but Capistrano provides its own integration with " \
   "Bundler via the capistrano-bundler gem. Use it instead."
diff --git a/lib/bundler/dsl.rb b/lib/bundler/dsl.rb
index 7424a5c8a4..534c9b5537 100644
--- a/lib/bundler/dsl.rb
+++ b/lib/bundler/dsl.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-require "bundler/dependency"
-require "bundler/ruby_dsl"
+require_relative "dependency"
+require_relative "ruby_dsl"
 
 module Bundler
   class Dsl
@@ -291,12 +291,7 @@ module Bundler
 "https://github.com/#{repo_name}.git"
         RUBY
         repo_name = "#{repo_name}/#{repo_name}" unless repo_name.include?("/")
-        if Bundler.feature_flag.github_https?
-          "https://github.com/#{repo_name}.git"
-        else
-          Bundler::SharedHelpers.major_deprecation 2, "Setting `github.https` to false is deprecated and won't be supported in the future."
-          "git://github.com/#{repo_name}.git"
-        end
+        "https://github.com/#{repo_name}.git"
       end
 
       git_source(:gist) do |repo_name|
diff --git a/lib/bundler/env.rb b/lib/bundler/env.rb
index 9cd9b8baca..a08db08aa0 100644
--- a/lib/bundler/env.rb
+++ b/lib/bundler/env.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-require "bundler/rubygems_integration"
-require "bundler/source/git/git_proxy"
+require_relative "rubygems_integration"
+require_relative "source/git/git_proxy"
 
 module Bundler
   class Env
@@ -100,8 +100,9 @@ module Bundler
       out << ["  Full Path", Gem.ruby]
       out << ["  Config Dir", Pathname.new(Gem::ConfigFile::SYSTEM_WIDE_CONFIG_FILE).dirname]
       out << ["RubyGems", Gem::VERSION]
-      out << ["  Gem Home", ENV.fetch("GEM_HOME") { Gem.dir }]
-      out << ["  Gem Path", ENV.fetch("GEM_PATH") { Gem.path.join(File::PATH_SEPARATOR) }]
+      out << ["  Gem Home", Gem.dir]
+      out << ["  Gem Path", Gem.path.join(File::PATH_SEPARATOR)]
+      out << ["  User Home", Gem.user_home]
       out << ["  User Path", Gem.user_dir]
       out << ["  Bin Dir", Gem.bindir]
       if defined?(OpenSSL)
diff --git a/lib/bundler/feature_flag.rb b/lib/bundler/feature_flag.rb
index 982f0fa540..a45694dd8e 100644
--- a/lib/bundler/feature_flag.rb
+++ b/lib/bundler/feature_flag.rb
@@ -36,16 +36,14 @@ module Bundler
     settings_flag(:default_install_uses_path) { bundler_3_mode? }
     settings_flag(:deployment_means_frozen) { bundler_3_mode? }
     settings_flag(:disable_multisource) { bundler_3_mode? }
-    settings_flag(:error_on_stderr) { bundler_2_mode? }
     settings_flag(:forget_cli_options) { bundler_3_mode? }
-    settings_flag(:global_path_appends_ruby_scope) { bundler_3_mode? }
     settings_flag(:global_gem_cache) { bundler_3_mode? }
     settings_flag(:only_update_to_newer_versions) { bundler_3_mode? }
     settings_flag(:path_relative_to_cwd) { bundler_3_mode? }
     settings_flag(:plugins) { @bundler_version >= Gem::Version.new("1.14") }
     settings_flag(:print_only_version_number) { bundler_3_mode? }
     settings_flag(:setup_makes_kernel_gem_public) { !bundler_3_mode? }
-    settings_flag(:skip_default_git_sources) { bundler_4_mode? }
+    settings_flag(:skip_default_git_sources) { bundler_3_mode? }
     settings_flag(:specific_platform) { bundler_3_mode? }
     settings_flag(:suppress_install_using_messages) { bundler_3_mode? }
     settings_flag(:unlock_source_unlocks_spec) { !bundler_3_mode? }
@@ -54,8 +52,6 @@ module Bundler
 
     settings_option(:default_cli_command) { bundler_3_mode? ? :cli_help : :install }
 
-    settings_method(:github_https?, "github.https") { bundler_2_mode? }
-
     def initialize(bundler_version)
       @bundler_version = Gem::Version.create(bundler_version)
     end
diff --git a/lib/bundler/fetcher.rb b/lib/bundler/fetcher.rb
index 8397f7b72b..d21baf659d 100644
--- a/lib/bundler/fetcher.rb
+++ b/lib/bundler/fetcher.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/vendored_persistent"
+require_relative "vendored_persistent"
 require "cgi"
 require "securerandom"
 require "zlib"
@@ -9,10 +9,10 @@ require "rubygems/request"
 module Bundler
   # Handles all the fetching with the rubygems server
   class Fetcher
-    autoload :CompactIndex, "bundler/fetcher/compact_index"
-    autoload :Downloader, "bundler/fetcher/downloader"
-    autoload :Dependency, "bundler/fetcher/dependency"
-    autoload :Index, "bundler/fetcher/index"
+    autoload :CompactIndex, File.expand_path("fetcher/compact_index", __dir__)
+    autoload :Downloader, File.expand_path("fetcher/downloader", __dir__)
+    autoload :Dependency, File.expand_path("fetcher/dependency", __dir__)
+    autoload :Index, File.expand_path("fetcher/index", __dir__)
 
     # This error is raised when it looks like the network is down
     class NetworkDownError < HTTPError; end
diff --git a/lib/bundler/fetcher/compact_index.rb b/lib/bundler/fetcher/compact_index.rb
index a117af72fa..f36d76d4ae 100644
--- a/lib/bundler/fetcher/compact_index.rb
+++ b/lib/bundler/fetcher/compact_index.rb
@@ -1,10 +1,10 @@
 # frozen_string_literal: true
 
-require "bundler/fetcher/base"
-require "bundler/worker"
+require_relative "base"
+require_relative "../worker"
 
 module Bundler
-  autoload :CompactIndexClient, "bundler/compact_index_client"
+  autoload :CompactIndexClient, File.expand_path("../compact_index_client", __dir__)
 
   class Fetcher
     class CompactIndex < Base
diff --git a/lib/bundler/fetcher/dependency.rb b/lib/bundler/fetcher/dependency.rb
index 1430d1ebeb..c52c32fb5b 100644
--- a/lib/bundler/fetcher/dependency.rb
+++ b/lib/bundler/fetcher/dependency.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/fetcher/base"
+require_relative "base"
 require "cgi"
 
 module Bundler
diff --git a/lib/bundler/fetcher/downloader.rb b/lib/bundler/fetcher/downloader.rb
index 2aeb9962c4..73f125af91 100644
--- a/lib/bundler/fetcher/downloader.rb
+++ b/lib/bundler/fetcher/downloader.rb
@@ -37,6 +37,7 @@ module Bundler
         when Net::HTTPTooManyRequests
           raise TooManyRequestsError, response.body
         when Net::HTTPUnauthorized
+          raise BadAuthenticationError, uri.host if uri.userinfo
           raise AuthenticationRequiredError, uri.host
         when Net::HTTPNotFound
           raise FallbackError, "Net::HTTPNotFound: #{URICredentialsFilter.credential_filtered_uri(uri)}"
diff --git a/lib/bundler/fetcher/index.rb b/lib/bundler/fetcher/index.rb
index 1a8064624d..9beb0e27d8 100644
--- a/lib/bundler/fetcher/index.rb
+++ b/lib/bundler/fetcher/index.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/fetcher/base"
+require_relative "base"
 require "rubygems/remote_fetcher"
 
 module Bundler
@@ -13,6 +13,7 @@ module Bundler
         when /certificate verify failed/
           raise CertificateFailureError.new(display_uri)
         when /401/
+          raise BadAuthenticationError, remote_uri if remote_uri.userinfo
           raise AuthenticationRequiredError, remote_uri
         when /403/
           raise BadAuthenticationError, remote_uri if remote_uri.userinfo
diff --git a/lib/bundler/friendly_errors.rb b/lib/bundler/friendly_errors.rb
index dd9b847f10..b93ae68012 100644
--- a/lib/bundler/friendly_errors.rb
+++ b/lib/bundler/friendly_errors.rb
@@ -1,11 +1,11 @@
 # frozen_string_literal: true
 
 require "cgi"
-require "bundler/vendored_thor"
+require_relative "vendored_thor"
 
 module Bundler
   module FriendlyErrors
-  module_function
+    module_function # rubocop:disable Layout/AccessModifierIndentation
 
     def log_error(error)
       case error
diff --git a/lib/bundler/gem_helper.rb b/lib/bundler/gem_helper.rb
index e9ee03b8a2..33f1d51592 100644
--- a/lib/bundler/gem_helper.rb
+++ b/lib/bundler/gem_helper.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-require "bundler/vendored_thor" unless defined?(Thor)
-require "bundler"
+require_relative "vendored_thor" unless defined?(Thor)
+require_relative "../bundler"
 require "shellwords"
 
 module Bundler
diff --git a/lib/bundler/gem_tasks.rb b/lib/bundler/gem_tasks.rb
index f736517bd7..bc725d3602 100644
--- a/lib/bundler/gem_tasks.rb
+++ b/lib/bundler/gem_tasks.rb
@@ -3,5 +3,5 @@
 require "rake/clean"
 CLOBBER.include "pkg"
 
-require "bundler/gem_helper"
+require_relative "gem_helper"
 Bundler::GemHelper.install_tasks
diff --git a/lib/bundler/gem_version_promoter.rb b/lib/bundler/gem_version_promoter.rb
index ed950ad28b..311b0cbbf3 100644
--- a/lib/bundler/gem_version_promoter.rb
+++ b/lib/bundler/gem_version_promoter.rb
@@ -81,8 +81,8 @@ module Bundler
           sort_dep_specs(spec_groups, locked_spec)
         end.tap do |specs|
           if DEBUG
-            STDERR.puts before_result
-            STDERR.puts " after sort_versions: #{debug_format_result(dep, specs).inspect}"
+            warn before_result
+            warn " after sort_versions: #{debug_format_result(dep, specs).inspect}"
           end
         end
       end
diff --git a/lib/bundler/injector.rb b/lib/bundler/injector.rb
index e67469f2dd..2cdda578e2 100644
--- a/lib/bundler/injector.rb
+++ b/lib/bundler/injector.rb
@@ -111,8 +111,10 @@ module Bundler
         end
 
         source = ", :source => \"#{d.source}\"" unless d.source.nil?
+        git = ", :git => \"#{d.git}\"" unless d.git.nil?
+        branch = ", :branch => \"#{d.branch}\"" unless d.branch.nil?
 
-        %(gem #{name}#{requirement}#{group}#{source})
+        %(gem #{name}#{requirement}#{group}#{source}#{git}#{branch})
       end.join("\n")
     end
 
diff --git a/lib/bundler/inline.rb b/lib/bundler/inline.rb
index 93355c9460..317bf892ab 100644
--- a/lib/bundler/inline.rb
+++ b/lib/bundler/inline.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/compatibility_guard"
+require_relative "compatibility_guard"
 
 # Allows for declaring a Gemfile inline in a ruby script, optionally installing
 # any gems that aren't already installed on the user's system.
@@ -32,7 +32,7 @@ require "bundler/compatibility_guard"
 #          puts Pod::VERSION # => "0.34.4"
 #
 def gemfile(install = false, options = {}, &gemfile)
-  require "bundler"
+  require_relative "../bundler"
 
   opts = options.dup
   ui = opts.delete(:ui) { Bundler::UI::Shell.new }
@@ -49,26 +49,28 @@ def gemfile(install = false, options = {}, &gemfile)
   builder = Bundler::Dsl.new
   builder.instance_eval(&gemfile)
 
-  definition = builder.to_definition(nil, true)
-  def definition.lock(*); end
-  definition.validate_runtime!
+  Bundler.settings.temporary(:frozen => false) do
+    definition = builder.to_definition(nil, true)
+    def definition.lock(*); end
+    definition.validate_runtime!
 
-  missing_specs = proc do
-    definition.missing_specs?
-  end
+    missing_specs = proc do
+      definition.missing_specs?
+    end
 
-  Bundler.ui = ui if install
-  if install || missing_specs.call
-    Bundler.settings.temporary(:inline => true) do
-      installer = Bundler::Installer.install(Bundler.root, definition, :system => true)
-      installer.post_install_messages.each do |name, message|
-        Bundler.ui.info "Post-install message from #{name}:\n#{message}"
+    Bundler.ui = ui if install
+    if install || missing_specs.call
+      Bundler.settings.temporary(:inline => true, :disable_platform_warnings => true) do
+        installer = Bundler::Installer.install(Bundler.root, definition, :system => true)
+        installer.post_install_messages.each do |name, message|
+          Bundler.ui.info "Post-install message from #{name}:\n#{message}"
+        end
       end
     end
-  end
 
-  runtime = Bundler::Runtime.new(nil, definition)
-  runtime.setup.require
+    runtime = Bundler::Runtime.new(nil, definition)
+    runtime.setup.require
+  end
 ensure
   bundler_module = class << Bundler; self; end
   bundler_module.send(:define_method, :root, old_root) if old_root
diff --git a/lib/bundler/installer.rb b/lib/bundler/installer.rb
index 49143b38f9..5bc53a8b61 100644
--- a/lib/bundler/installer.rb
+++ b/lib/bundler/installer.rb
@@ -2,10 +2,10 @@
 
 require "erb"
 require "rubygems/dependency_installer"
-require "bundler/worker"
-require "bundler/installer/parallel_installer"
-require "bundler/installer/standalone"
-require "bundler/installer/gem_installer"
+require_relative "worker"
+require_relative "installer/parallel_installer"
+require_relative "installer/standalone"
+require_relative "installer/gem_installer"
 
 module Bundler
   class Installer
diff --git a/lib/bundler/installer/parallel_installer.rb b/lib/bundler/installer/parallel_installer.rb
index 469b15b96c..391540af0b 100644
--- a/lib/bundler/installer/parallel_installer.rb
+++ b/lib/bundler/installer/parallel_installer.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
-require "bundler/worker"
-require "bundler/installer/gem_installer"
+require_relative "../worker"
+require_relative "gem_installer"
 
 module Bundler
   class ParallelInstaller
diff --git a/lib/bundler/lazy_specification.rb b/lib/bundler/lazy_specification.rb
index 69a721c120..cbd04b2c90 100644
--- a/lib/bundler/lazy_specification.rb
+++ b/lib/bundler/lazy_specification.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 require "uri"
-require "bundler/match_platform"
+require_relative "match_platform"
 
 module Bundler
   class LazySpecification
diff --git a/lib/bundler/lockfile_parser.rb b/lib/bundler/lockfile_parser.rb
index 50dc1381fe..5658ec1205 100644
--- a/lib/bundler/lockfile_parser.rb
+++ b/lib/bundler/lockfile_parser.rb
@@ -101,17 +101,11 @@ module Bundler
       return unless bundler_version
       prerelease_text = bundler_version.prerelease? ? " --pre" : ""
       current_version = Gem::Version.create(Bundler::VERSION)
-      case current_version.segments.first <=> bundler_version.segments.first
-      when -1
-        raise LockfileError, "You must use Bundler #{bundler_version.segments.first} or greater with this lockfile."
-      when 0
-        if current_version < bundler_version
-          Bundler.ui.warn "Warning: the running version of Bundler (#{current_version}) is older " \
-               "than the version that created the lockfile (#{bundler_version}). We suggest you to " \
-               "upgrade to the version that created the lockfile by running `gem install " \
-               "bundler:#{bundler_version}#{prerelease_text}`.\n"
-        end
-      end
+      return unless current_version < bundler_version
+      Bundler.ui.warn "Warning: the running version of Bundler (#{current_version}) is older " \
+           "than the version that created the lockfile (#{bundler_version}). We suggest you to " \
+           "upgrade to the version that created the lockfile by running `gem install " \
+           "bundler:#{bundler_version}#{prerelease_text}`.\n"
     end
 
   private
diff --git a/lib/bundler/match_platform.rb b/lib/bundler/match_platform.rb
index 56cbbfb95d..69074925a6 100644
--- a/lib/bundler/match_platform.rb
+++ b/lib/bundler/match_platform.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/gem_helpers"
+require_relative "gem_helpers"
 
 module Bundler
   module MatchPlatform
diff --git a/lib/bundler/plugin.rb b/lib/bundler/plugin.rb
index 996d29aafb..ffb3ee9883 100644
--- a/lib/bundler/plugin.rb
+++ b/lib/bundler/plugin.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/plugin/api"
+require_relative "plugin/api"
 
 module Bundler
   module Plugin
@@ -256,7 +256,7 @@ module Bundler
       @hooks_by_event = Hash.new {|h, k| h[k] = [] }
 
       load_paths = spec.load_paths
-      add_to_load_path(load_paths)
+      Bundler.rubygems.add_to_load_path(load_paths)
       path = Pathname.new spec.full_gem_path
 
       begin
@@ -288,7 +288,7 @@ module Bundler
       # done to avoid conflicts
       path = index.plugin_path(name)
 
-      add_to_load_path(index.load_paths(name))
+      Bundler.rubygems.add_to_load_path(index.load_paths(name))
 
       load path.join(PLUGIN_FILE_NAME)
 
@@ -298,17 +298,8 @@ module Bundler
       raise
     end
 
-    def add_to_load_path(load_paths)
-      if insert_index = Bundler.rubygems.load_path_insert_index
-        $LOAD_PATH.insert(insert_index, *load_paths)
-      else
-        $LOAD_PATH.unshift(*load_paths)
-      end
-    end
-
     class << self
-      private :load_plugin, :register_plugin, :save_plugins, :validate_plugin!,
-        :add_to_load_path
+      private :load_plugin, :register_plugin, :save_plugins, :validate_plugin!
     end
   end
 end
diff --git a/lib/bundler/plugin/api.rb b/lib/bundler/plugin/api.rb
index a2d5cbb4ac..ee2bffe3ab 100644
--- a/lib/bundler/plugin/api.rb
+++ b/lib/bundler/plugin/api.rb
@@ -23,7 +23,7 @@ module Bundler
   # and hooks).
   module Plugin
     class API
-      autoload :Source, "bundler/plugin/api/source"
+      autoload :Source, File.expand_path("api/source", __dir__)
 
       # The plugins should declare that they handle a command through this helper.
       #
diff --git a/lib/bundler/plugin/index.rb b/lib/bundler/plugin/index.rb
index faabf3a8d1..2d70a046bb 100644
--- a/lib/bundler/plugin/index.rb
+++ b/lib/bundler/plugin/index.rb
@@ -139,7 +139,7 @@ module Bundler
 
           data = index_f.read
 
-          require "bundler/yaml_serializer"
+          require_relative "../yaml_serializer"
           index = YAMLSerializer.load(data)
 
           @commands.merge!(index["commands"])
@@ -162,7 +162,7 @@ module Bundler
           "sources"      => @sources,
         }
 
-        require "bundler/yaml_serializer"
+        require_relative "../yaml_serializer"
         SharedHelpers.filesystem_access(index_file) do |index_f|
           FileUtils.mkdir_p(index_f.dirname)
           File.open(index_f, "w") {|f| f.puts YAMLSerializer.dump(index) }
diff --git a/lib/bundler/plugin/installer.rb b/lib/bundler/plugin/installer.rb
index 4a262efac2..bcea3f0e45 100644
--- a/lib/bundler/plugin/installer.rb
+++ b/lib/bundler/plugin/installer.rb
@@ -8,8 +8,8 @@ module Bundler
   # are heavily dependent on the Gemfile.
   module Plugin
     class Installer
-      autoload :Rubygems, "bundler/plugin/installer/rubygems"
-      autoload :Git,      "bundler/plugin/installer/git"
+      autoload :Rubygems, File.expand_path("installer/rubygems", __dir__)
+      autoload :Git,      File.expand_path("installer/git", __dir__)
 
       def install(names, options)
         check_sources_consistency!(options)
diff --git a/lib/bundler/psyched_yaml.rb b/lib/bundler/psyched_yaml.rb
index e654416a5a..c086b7651c 100644
--- a/lib/bundler/psyched_yaml.rb
+++ b/lib/bundler/psyched_yaml.rb
@@ -27,7 +27,7 @@ module Bundler
   end
 end
 
-require "bundler/deprecate"
+require_relative "deprecate"
 begin
   Bundler::Deprecate.skip_during do
     require "rubygems/safe_yaml"
diff --git a/lib/bundler/resolver.rb b/lib/bundler/resolver.rb
index 90f833bef1..c7caf01c7d 100644
--- a/lib/bundler/resolver.rb
+++ b/lib/bundler/resolver.rb
@@ -2,8 +2,8 @@
 
 module Bundler
   class Resolver
-    require "bundler/vendored_molinillo"
-    require "bundler/resolver/spec_group"
+    require_relative "vendored_molinillo"
+    require_relative "resolver/spec_group"
 
     # Figures out the best possible configuration of gems that satisfies
     # the list of passed dependencies and any child dependencies without
@@ -75,7 +75,7 @@ module Bundler
       return unless debug?
       debug_info = yield
       debug_info = debug_info.inspect unless debug_info.is_a?(String)
-      STDERR.puts debug_info.split("\n").map {|s| "  " * depth + s }
+      warn debug_info.split("\n").map {|s| "  " * depth + s }
     end
 
     def debug?
diff --git a/lib/bundler/rubygems_ext.rb b/lib/bundler/rubygems_ext.rb
index ccf71c8c00..96b93836c7 100644
--- a/lib/bundler/rubygems_ext.rb
+++ b/lib/bundler/rubygems_ext.rb
@@ -4,40 +4,25 @@ require "pathname"
 
 require "rubygems/specification"
 
-begin
-  # Possible use in Gem::Specification#source below and require
-  # shouldn't be deferred.
-  require "rubygems/source"
-rescue LoadError
-  # Not available before RubyGems 2.0.0, ignore
-  nil
-end
+# Possible use in Gem::Specification#source below and require
+# shouldn't be deferred.
+require "rubygems/source"
 
-require "bundler/match_platform"
+require_relative "match_platform"
 
 module Gem
-  @loaded_stacks = Hash.new {|h, k| h[k] = [] }
-
   class Specification
     attr_accessor :remote, :location, :relative_loaded_from
 
-    if instance_methods(false).include?(:source)
-      remove_method :source
-      attr_writer :source
-      def source
-        (defined?(@source) && @source) || Gem::Source::Installed.new
-      end
-    else
-      # rubocop:disable Lint/DuplicateMethods
-      attr_accessor :source
-      # rubocop:enable Lint/DuplicateMethods
+    remove_method :source
+    attr_writer :source
+    def source
+      (defined?(@source) && @source) || Gem::Source::Installed.new
     end
 
     alias_method :rg_full_gem_path, :full_gem_path
     alias_method :rg_loaded_from,   :loaded_from
 
-    attr_writer :full_gem_path unless instance_methods.include?(:full_gem_path=)
-
     def full_gem_path
       # this cannot check source.is_a?(Bundler::Plugin::API::Source)
       # because that _could_ trip the autoload, and if there are unresolved
@@ -59,15 +44,7 @@ module Gem
     end
 
     def load_paths
-      return full_require_paths if respond_to?(:full_require_paths)
-
-      require_paths.map do |require_path|
-        if require_path.include?(full_gem_path)
-          require_path
-        else
-          File.join(full_gem_path, require_path)
-        end
-      end
+      full_require_paths
     end
 
     if method_defined?(:extension_dir)
@@ -151,32 +128,6 @@ module Gem
       end
       out
     end
-
-    # Backport of performance enhancement added to RubyGems 1.4
-    def matches_spec?(spec)
-      # name can be a Regexp, so use ===
-      return false unless name === spec.name
-      return true  if requirement.none?
-
-      requirement.satisfied_by?(spec.version)
-    end unless allocate.respond_to?(:matches_spec?)
-  end
-
-  class Requirement
-    # Backport of performance enhancement added to RubyGems 1.4
-    def none?
-      # note that it might be tempting to replace with with RubyGems 2.0's
-      # improved implementation. Don't. It requires `DefaultRequirement` to be
-      # defined, and more importantantly, these overrides are not used when the
-      # running RubyGems defines these methods
-      to_s == ">= 0"
-    end unless allocate.respond_to?(:none?)
-
-    # Backport of performance enhancement added to RubyGems 2.2
-    def exact?
-      return false unless @requirements.size == 1
-      @requirements[0][0] == "="
-    end unless allocate.respond_to?(:exact?)
   end
 
   class Platform
diff --git a/lib/bundler/rubygems_integration.rb b/lib/bundler/rubygems_integration.rb
index a4519246a9..9df0897ca2 100644
--- a/lib/bundler/rubygems_integration.rb
+++ b/lib/bundler/rubygems_integration.rb
@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 
-require "monitor"
-
 module Bundler
   class RubygemsIntegration
     if defined?(Gem::Ext::Builder::CHDIR_MONITOR)
       EXT_LOCK = Gem::Ext::Builder::CHDIR_MONITOR
     else
+      require "monitor"
+
       EXT_LOCK = Monitor.new
     end
 
@@ -20,6 +20,7 @@ module Bundler
 
     def initialize
       @replaced_methods = {}
+      backport_ext_builder_monitor
     end
 
     def version
@@ -38,14 +39,22 @@ module Bundler
       Gem::Command.build_args = args
     end
 
-    def load_path_insert_index
-      Gem.load_path_insert_index
-    end
-
     def loaded_specs(name)
       Gem.loaded_specs[name]
     end
 
+    def add_to_load_path(paths)
+      return Gem.add_to_load_path(*paths) if Gem.respond_to?(:add_to_load_path)
+
+      if insert_index = Gem.load_path_insert_index
+        # Gem directories must come after -I and ENV['RUBYLIB']
+        $LOAD_PATH.insert(insert_index, *paths)
+      else
+        # We are probably testing in core, -I and RUBYLIB don't apply
+        $LOAD_PATH.unshift(*paths)
+      end
+    end
+
     def mark_loaded(spec)
       if spec.respond_to?(:activated=)
         current = Gem.loaded_specs[spec.name]
@@ -110,7 +119,7 @@ module Bundler
     end
 
     def configuration
-      require "bundler/psyched_yaml"
+      require_relative "psyched_yaml"
       Gem.configuration
     rescue Gem::SystemExitException, LoadError => e
       Bundler.ui.error "#{e.class}: #{e.message}"
@@ -198,10 +207,6 @@ module Bundler
       Gem::ConfigMap
     end
 
-    def repository_subdirectories
-      %w[cache doc gems specifications]
-    end
-
     def clear_paths
       Gem.clear_paths
     end
@@ -210,26 +215,14 @@ module Bundler
       Gem.bin_path(gem, bin, ver)
     end
 
-    def path_separator
-      File::PATH_SEPARATOR
-    end
-
     def preserve_paths
       # this is a no-op outside of RubyGems 1.8
       yield
     end
 
     def loaded_gem_paths
-      # RubyGems 2.2+ can put binary extension into dedicated folders,
-      # therefore use RubyGems facilities to obtain their load paths.
-      if Gem::Specification.method_defined? :full_require_paths
-        loaded_gem_paths = Gem.loaded_specs.map {|_, s| s.full_require_paths }
-        loaded_gem_paths.flatten
-      else
-        $LOAD_PATH.select do |p|
-          Bundler.rubygems.gem_path.any? {|gp| p =~ /^#{Regexp.escape(gp)}/ }
-        end
-      end
+      loaded_gem_paths = Gem.loaded_specs.map {|_, s| s.full_require_paths }
+      loaded_gem_paths.flatten
     end
 
     def load_plugins
@@ -248,36 +241,12 @@ module Bundler
       EXT_LOCK
     end
 
-    def fetch_specs(all, pre, &blk)
-      require "rubygems/spec_fetcher"
-      specs = Gem::SpecFetcher.new.list(all, pre)
-      specs.each { yield } if block_given?
-      specs
-    end
-
     def fetch_prerelease_specs
       fetch_specs(false, true)
     rescue Gem::RemoteFetcher::FetchError
       {} # if we can't download them, there aren't any
     end
 
-    # TODO: This is for older versions of RubyGems... should we support the
-    # X-Gemfile-Source header on these old versions?
-    # Maybe the newer implementation will work on older RubyGems?
-    # It seems difficult to keep this implementation and still send the header.
-    def fetch_all_remote_specs(remote)
-      old_sources = Bundler.rubygems.sources
-      Bundler.rubygems.sources = [remote.uri.to_s]
-      # Fetch all specs, minus prerelease specs
-      spec_list = fetch_specs(true, false)
-      # Then fetch the prerelease specs
-      fetch_prerelease_specs.each {|k, v| spec_list[k].concat(v) }
-
-      spec_list.values.first
-    ensure
-      Bundler.rubygems.sources = old_sources
-    end
-
     def with_build_args(args)
       ext_lock.synchronize do
         old_args = build_args
@@ -290,18 +259,9 @@ module Bundler
       end
     end
 
-    def install_with_build_args(args)
-      with_build_args(args) { yield }
-    end
-
-    def gem_from_path(path, policy = nil)
-      require "rubygems/format"
-      Gem::Format.from_file_by_path(path, policy)
-    end
-
     def spec_from_gem(path, policy = nil)
       require "rubygems/security"
-      require "bundler/psyched_yaml"
+      require_relative "psyched_yaml"
       gem_from_path(path, security_policies[policy]).spec
     rescue Gem::Package::FormatError
       raise GemspecError, "Could not read gem at #{path}. It may be corrupted."
@@ -317,23 +277,10 @@ module Bundler
       end
     end
 
-    def build(spec, skip_validation = false)
-      require "rubygems/builder"
-      Gem::Builder.new(spec).build
-    end
-
     def build_gem(gem_dir, spec)
       build(spec)
     end
 
-    def download_gem(spec, uri, path)
-      uri = Bundler.settings.mirror_for(uri)
-      fetcher = Gem::RemoteFetcher.new(configuration[:http_proxy])
-      Bundler::Retry.new("download gem from #{uri}").attempts do
-        fetcher.download(spec, uri, path)
-      end
-    end
-
     def security_policy_keys
       %w[High Medium Low AlmostNo No].map {|level| "#{level}Security" }
     end
@@ -357,12 +304,17 @@ module Bundler
       end
     end
 
+    # RubyGems-generated binstubs call Kernel#gem
     def binstubs_call_gem?
-      true
+      !provides?(">= 2.5.2")
     end
 
+    # only 2.5.2+ has all of the stub methods we want to use, and since this
+    # is a performance optimization _only_,
+    # we'll restrict ourselves to the most
+    # recent RG versions instead of all versions that have stubs
     def stubs_provide_full_functionality?
-      false
+      provides?(">= 2.5.2")
     end
 
     def replace_gem(specs, specs_by_name)
@@ -411,26 +363,6 @@ module Bundler
       end
     end
 
-    def stub_source_index(specs)
-      Gem::SourceIndex.send(:alias_method, :old_initialize, :initialize)
-      redefine_method(Gem::SourceIndex, :initialize) do |*args|
-        @gems = {}
-        # You're looking at this thinking: Oh! This is how I make those
-        # rubygems deprecations go away!
-        #
-        # You'd be correct BUT using of this method in production code
-        # must be approved by the rubygems team itself!
-        #
-        # This is your warning. If you use this and don't have approval
-        # we can't protect you.
-        #
-        Deprecate.skip_during do
-          self.spec_dirs = *args
-          add_specs(*specs)
-        end
-      end
-    end
-
     # Used to make bin stubs that are not created by bundler work
     # under bundler. The new Gem.bin_path only considers gems in
     # +specs+
@@ -531,25 +463,6 @@ module Bundler
       Gem.clear_paths
     end
 
-    # This backports the correct segment generation code from RubyGems 1.4+
-    # by monkeypatching it into the method in RubyGems 1.3.6 and 1.3.7.
-    def backport_segment_generation
-      redefine_method(Gem::Version, :segments) do
-        @segments ||= @version.scan(/[0-9]+|[a-z]+/i).map do |s|
-          /^\d+$/ =~ s ? s.to_i : s
-        end
-      end
-    end
-
-    # This backport fixes the marshaling of @segments.
-    def backport_yaml_initialize
-      redefine_method(Gem::Version, :yaml_initialize) do |_, map|
-        @version = map["version"]
-        @segments = nil
-        @hash = nil
-      end
-    end
-
     # This backports base_dir which replaces installation path
     # RubyGems 1.8+
     def backport_base_dir
@@ -622,296 +535,129 @@ module Bundler
       end
     end
 
-    # RubyGems 1.4 through 1.6
-    class Legacy < RubygemsIntegration
-      def initialize
-        super
-        backport_base_dir
-        backport_cache_file
-        backport_spec_file
-        backport_yaml_initialize
-      end
+    def stub_rubygems(specs)
+      Gem::Specification.all = specs
 
-      def stub_rubygems(specs)
-        # RubyGems versions lower than 1.7 use SourceIndex#from_gems_in
-        source_index_class = (class << Gem::SourceIndex; self; end)
-        redefine_method(source_index_class, :from_gems_in) do |*args|
-          Gem::SourceIndex.new.tap do |source_index|
-            source_index.spec_dirs = *args
-            source_index.add_specs(*specs)
-          end
-        end
+      Gem.post_reset do
+        Gem::Specification.all = specs
       end
 
-      def all_specs
-        Gem.source_index.gems.values
+      redefine_method((class << Gem; self; end), :finish_resolve) do |*|
+        []
       end
+    end
 
-      def find_name(name)
-        Gem.source_index.find_name(name)
-      end
+    def fetch_specs(source, remote, name)
+      path = source + "#{name}.#{Gem.marshal_version}.gz"
+      fetcher = gem_remote_fetcher
+      fetcher.headers = { "X-Gemfile-Source" => remote.original_uri.to_s } if remote.original_uri
+      string = fetcher.fetch_path(path)
+      Bundler.load_marshal(string)
+    rescue Gem::RemoteFetcher::FetchError => e
+      # it's okay for prerelease to fail
+      raise e unless name == "prerelease_specs"
+    end
 
-      def validate(spec)
-        # These versions of RubyGems always validate in "packaging" mode,
-        # which is too strict for the kinds of checks we care about. As a
-        # result, validation is disabled on versions of RubyGems below 1.7.
-      end
+    def fetch_all_remote_specs(remote)
+      source = remote.uri.is_a?(URI) ? remote.uri : URI.parse(source.to_s)
 
-      def post_reset_hooks
-        []
-      end
+      specs = fetch_specs(source, remote, "specs")
+      pres = fetch_specs(source, remote, "prerelease_specs") || []
 
-      def reset
-      end
+      specs.concat(pres)
     end
 
-    # RubyGems versions 1.3.6 and 1.3.7
-    class Ancient < Legacy
-      def initialize
-        super
-        backport_segment_generation
+    def download_gem(spec, uri, path)
+      uri = Bundler.settings.mirror_for(uri)
+      fetcher = gem_remote_fetcher
+      fetcher.headers = { "X-Gemfile-Source" => spec.remote.original_uri.to_s } if spec.remote.original_uri
+      Bundler::Retry.new("download gem from #{uri}").attempts do
+        fetcher.download(spec, uri, path)
       end
     end
 
-    # RubyGems 1.7
-    class Transitional < Legacy
-      def stub_rubygems(specs)
-        stub_source_index(specs)
-      end
-
-      def validate(spec)
-        # Missing summary is downgraded to a warning in later versions,
-        # so we set it to an empty string to prevent an exception here.
-        spec.summary ||= ""
-        RubygemsIntegration.instance_method(:validate).bind(self).call(spec)
-      end
+    def gem_remote_fetcher
+      require "resolv"
+      proxy = configuration[:http_proxy]
+      dns = Resolv::DNS.new
+      Bundler::GemRemoteFetcher.new(proxy, dns)
     end
 
-    # RubyGems 1.8.5-1.8.19
-    class Modern < RubygemsIntegration
-      def stub_rubygems(specs)
-        Gem::Specification.all = specs
-
-        Gem.post_reset do
-          Gem::Specification.all = specs
-        end
+    def gem_from_path(path, policy = nil)
+      require "rubygems/package"
+      p = Gem::Package.new(path)
+      p.security_policy = policy if policy
+      p
+    end
 
-        stub_source_index(specs)
-      end
+    def build(spec, skip_validation = false)
+      require "rubygems/package"
+      Gem::Package.build(spec, skip_validation)
+    end
 
-      def all_specs
-        Gem::Specification.to_a
-      end
+    def repository_subdirectories
+      Gem::REPOSITORY_SUBDIRECTORIES
+    end
 
-      def find_name(name)
-        Gem::Specification.find_all_by_name name
-      end
+    def install_with_build_args(args)
+      yield
     end
 
-    # RubyGems 1.8.0 to 1.8.4
-    class AlmostModern < Modern
-      # RubyGems [>= 1.8.0, < 1.8.5] has a bug that changes Gem.dir whenever
-      # you call Gem::Installer#install with an :install_dir set. We have to
-      # change it back for our sudo mode to work.
-      def preserve_paths
-        old_dir = gem_dir
-        old_path = gem_path
-        yield
-        Gem.use_paths(old_dir, old_path)
-      end
+    def path_separator
+      Gem.path_separator
     end
 
-    # RubyGems 1.8.20+
-    class MoreModern < Modern
-      # RubyGems 1.8.20 and adds the skip_validation parameter, so that's
-      # when we start passing it through.
-      def build(spec, skip_validation = false)
-        require "rubygems/builder"
-        Gem::Builder.new(spec).build(skip_validation)
+    def all_specs
+      require_relative "remote_specification"
+      Gem::Specification.stubs.map do |stub|
+        StubSpecification.from_stub(stub)
       end
     end
 
-    # RubyGems 2.0
-    class Future < RubygemsIntegration
-      def stub_rubygems(specs)
-        Gem::Specification.all = specs
-
-        Gem.post_reset do
-          Gem::Specification.all = specs
+    def backport_ext_builder_monitor
+      # So we can avoid requiring "rubygems/ext" in its entirety
+      Gem.module_eval <<-RB, __FILE__, __LINE__ + 1
+        module Ext
         end
+      RB
 
-        redefine_method((class << Gem; self; end), :finish_resolve) do |*|
-          []
-        end
-      end
-
-      def all_specs
-        Gem::Specification.to_a
-      end
-
-      def find_name(name)
-        Gem::Specification.find_all_by_name name
-      end
-
-      def fetch_specs(source, remote, name)
-        path = source + "#{name}.#{Gem.marshal_version}.gz"
-        fetcher = gem_remote_fetcher
-        fetcher.headers = { "X-Gemfile-Source" => remote.original_uri.to_s } if remote.original_uri
-        string = fetcher.fetch_path(path)
-        Bundler.load_marshal(string)
-      rescue Gem::RemoteFetcher::FetchError => e
-        # it's okay for prerelease to fail
-        raise e unless name == "prerelease_specs"
-      end
-
-      def fetch_all_remote_specs(remote)
-        source = remote.uri.is_a?(URI) ? remote.uri : URI.parse(source.to_s)
+      require "rubygems/ext/builder"
 
-        specs = fetch_specs(source, remote, "specs")
-        pres = fetch_specs(source, remote, "prerelease_specs") || []
-
-        specs.concat(pres)
-      end
-
-      def download_gem(spec, uri, path)
-        uri = Bundler.settings.mirror_for(uri)
-        fetcher = gem_remote_fetcher
-        fetcher.headers = { "X-Gemfile-Source" => spec.remote.original_uri.to_s } if spec.remote.original_uri
-        Bundler::Retry.new("download gem from #{uri}").attempts do
-          fetcher.download(spec, uri, path)
+      Gem::Ext::Builder.class_eval do
+        unless const_defined?(:CHDIR_MONITOR)
+          const_set(:CHDIR_MONITOR, EXT_LOCK)
         end
-      end
-
-      def gem_remote_fetcher
-        require "resolv"
-        proxy = configuration[:http_proxy]
-        dns = Resolv::DNS.new
-        Bundler::GemRemoteFetcher.new(proxy, dns)
-      end
-
-      def gem_from_path(path, policy = nil)
-        require "rubygems/package"
-        p = Gem::Package.new(path)
-        p.security_policy = policy if policy
-        p
-      end
 
-      def build(spec, skip_validation = false)
-        require "rubygems/package"
-        Gem::Package.build(spec, skip_validation)
-      end
-
-      def repository_subdirectories
-        Gem::REPOSITORY_SUBDIRECTORIES
-      end
-
-      def install_with_build_args(args)
-        yield
-      end
-
-      def path_separator
-        Gem.path_separator
+        remove_const(:CHDIR_MUTEX) if const_defined?(:CHDIR_MUTEX)
+        const_set(:CHDIR_MUTEX, const_get(:CHDIR_MONITOR))
       end
     end
 
-    # RubyGems 2.1.0
-    class MoreFuture < Future
-      def initialize
-        super
-        backport_ext_builder_monitor
-      end
-
-      def all_specs
-        require "bundler/remote_specification"
-        Gem::Specification.stubs.map do |stub|
-          StubSpecification.from_stub(stub)
-        end
-      end
-
-      def backport_ext_builder_monitor
-        # So we can avoid requiring "rubygems/ext" in its entirety
-        Gem.module_eval <<-RB, __FILE__, __LINE__ + 1
-          module Ext
-          end
-        RB
-
-        require "rubygems/ext/builder"
-
-        Gem::Ext::Builder.class_eval do
-          unless const_defined?(:CHDIR_MONITOR)
-            const_set(:CHDIR_MONITOR, EXT_LOCK)
-          end
-
-          remove_const(:CHDIR_MUTEX) if const_defined?(:CHDIR_MUTEX)
-          const_set(:CHDIR_MUTEX, const_get(:CHDIR_MONITOR))
-        end
-      end
-
-      if Gem::Specification.respond_to?(:stubs_for)
-        def find_name(name)
-          Gem::Specification.stubs_for(name).map(&:to_spec)
-        end
-      else
-        def find_name(name)
-          Gem::Specification.stubs.find_all do |spec|
-            spec.name == name
-          end.map(&:to_spec)
-        end
-      end
+    def find_name(name)
+      Gem::Specification.stubs_for(name).map(&:to_spec)
+    end
 
-      if Gem::Specification.respond_to?(:default_stubs)
-        def default_stubs
-          Gem::Specification.default_stubs("*.gemspec")
-        end
-      else
-        def default_stubs
-          Gem::Specification.send(:default_stubs, "*.gemspec")
-        end
+    if Gem::Specification.respond_to?(:default_stubs)
+      def default_stubs
+        Gem::Specification.default_stubs("*.gemspec")
       end
-
-      def use_gemdeps(gemfile)
-        ENV["BUNDLE_GEMFILE"] ||= File.expand_path(gemfile)
-        require "bundler/gemdeps"
-        runtime = Bundler.setup
-        Bundler.ui = nil
-        activated_spec_names = runtime.requested_specs.map(&:to_spec).sort_by(&:name)
-        [Gemdeps.new(runtime), activated_spec_names]
+    else
+      def default_stubs
+        Gem::Specification.send(:default_stubs, "*.gemspec")
       end
+    end
 
-      if provides?(">= 2.5.2")
-        # RubyGems-generated binstubs call Kernel#gem
-        def binstubs_call_gem?
-          false
-        end
-
-        # only 2.5.2+ has all of the stub methods we want to use, and since this
-        # is a performance optimization _only_,
-        # we'll restrict ourselves to the most
-        # recent RG versions instead of all versions that have stubs
-        def stubs_provide_full_functionality?
-          true
-        end
-      end
+    def use_gemdeps(gemfile)
+      ENV["BUNDLE_GEMFILE"] ||= File.expand_path(gemfile)
+      require_relative "gemdeps"
+      runtime = Bundler.setup
+      Bundler.ui = nil
+      activated_spec_names = runtime.requested_specs.map(&:to_spec).sort_by(&:name)
+      [Gemdeps.new(runtime), activated_spec_names]
     end
   end
 
   def self.rubygems
-    @rubygems ||= if RubygemsIntegration.provides?(">= 2.1.0")
-      RubygemsIntegration::MoreFuture.new
-    elsif RubygemsIntegration.provides?(">= 1.99.99")
-      RubygemsIntegration::Future.new
-    elsif RubygemsIntegration.provides?(">= 1.8.20")
-      RubygemsIntegration::MoreModern.new
-    elsif RubygemsIntegration.provides?(">= 1.8.5")
-      RubygemsIntegration::Modern.new
-    elsif RubygemsIntegration.provides?(">= 1.8.0")
-      RubygemsIntegration::AlmostModern.new
-    elsif RubygemsIntegration.provides?(">= 1.7.0")
-      RubygemsIntegration::Transitional.new
-    elsif RubygemsIntegration.provides?(">= 1.4.0")
-      RubygemsIntegration::Legacy.new
-    else # RubyGems 1.3.6 and 1.3.7
-      RubygemsIntegration::Ancient.new
-    end
+    @rubygems ||= RubygemsIntegration.new
   end
 end
diff --git a/lib/bundler/runtime.rb b/lib/bundler/runtime.rb
index 83945868f9..93a801eb6c 100644
--- a/lib/bundler/runtime.rb
+++ b/lib/bundler/runtime.rb
@@ -34,14 +34,7 @@ module Bundler
         spec.load_paths.reject {|path| $LOAD_PATH.include?(path) }
       end.reverse.flatten
 
-      # See Gem::Specification#add_self_to_load_path (since RubyGems 1.8)
-      if insert_index = Bundler.rubygems.load_path_insert_index
-        # Gem directories must come after -I and ENV['RUBYLIB']
-        $LOAD_PATH.insert(insert_index, *load_paths)
-      else
-        # We are probably testing in core, -I and RUBYLIB don't apply
-        $LOAD_PATH.unshift(*load_paths)
-      end
+      Bundler.rubygems.add_to_load_path(load_paths)
 
       setup_manpath
 
diff --git a/lib/bundler/settings.rb b/lib/bundler/settings.rb
index 5bc190865f..3888ac51d3 100644
--- a/lib/bundler/settings.rb
+++ b/lib/bundler/settings.rb
@@ -4,9 +4,9 @@ require "uri"
 
 module Bundler
   class Settings
-    autoload :Mirror,  "bundler/mirror"
-    autoload :Mirrors, "bundler/mirror"
-    autoload :Validator, "bundler/settings/validator"
+    autoload :Mirror,  File.expand_path("mirror", __dir__)
+    autoload :Mirrors, File.expand_path("mirror", __dir__)
+    autoload :Validator, File.expand_path("settings/validator", __dir__)
 
     BOOL_KEYS = %w[
       allow_bundler_dependency_conflicts
@@ -28,14 +28,11 @@ module Bundler
       disable_platform_warnings
       disable_shared_gems
       disable_version_check
-      error_on_stderr
       force_ruby_platform
       forget_cli_options
       frozen
       gem.coc
       gem.mit
-      github.https
-      global_path_appends_ruby_scope
       global_gem_cache
       ignore_messages
       init_gems_rb
@@ -207,23 +204,22 @@ module Bundler
       locations
     end
 
-    # for legacy reasons, in Bundler 1, the ruby scope isnt appended when the setting comes from ENV or the global config,
-    # nor do we respect :disable_shared_gems
+    # for legacy reasons, in Bundler 2, we do not respect :disable_shared_gems
     def path
       key  = key_for(:path)
       path = ENV[key] || @global_config[key]
       if path && !@temporary.key?(key) && !@local_config.key?(key)
-        return Path.new(path, Bundler.feature_flag.global_path_appends_ruby_scope?, false, false)
+        return Path.new(path, false, false)
       end
 
       system_path = self["path.system"] || (self[:disable_shared_gems] == false)
-      Path.new(self[:path], true, system_path, Bundler.feature_flag.default_install_uses_path?)
+      Path.new(self[:path], system_path, Bundler.feature_flag.default_install_uses_path?)
     end
 
-    Path = Struct.new(:explicit_path, :append_ruby_scope, :system_path, :default_install_uses_path) do
+    Path = Struct.new(:explicit_path, :system_path, :default_install_uses_path) do
       def path
         path = base_path
-        path = File.join(path, Bundler.ruby_scope) if append_ruby_scope && !use_system_gems?
+        path = File.join(path, Bundler.ruby_scope) unless use_system_gems?
         path
       end
 
@@ -358,7 +354,7 @@ module Bundler
       return unless file
       SharedHelpers.filesystem_access(file) do |p|
         FileUtils.mkdir_p(p.dirname)
-        require "bundler/yaml_serializer"
+        require_relative "yaml_serializer"
         p.open("w") {|f| f.write(YAMLSerializer.dump(hash)) }
       end
     end
@@ -398,7 +394,7 @@ module Bundler
       SharedHelpers.filesystem_access(config_file, :read) do |file|
         valid_file = file.exist? && !file.size.zero?
         return {} unless valid_file
-        require "bundler/yaml_serializer"
+        require_relative "yaml_serializer"
         YAMLSerializer.load file.read
       end
     end
diff --git a/lib/bundler/setup.rb b/lib/bundler/setup.rb
index 52a5b8889a..d156f494a8 100644
--- a/lib/bundler/setup.rb
+++ b/lib/bundler/setup.rb
@@ -1,9 +1,9 @@
 # frozen_string_literal: true
 
-require "bundler/shared_helpers"
+require_relative "shared_helpers"
 
 if Bundler::SharedHelpers.in_bundle?
-  require "bundler"
+  require_relative "../bundler"
 
   if STDOUT.tty? || ENV["BUNDLER_FORCE_TTY"]
     Bundler.ui = Bundler::UI::Shell.new
diff --git a/lib/bundler/shared_helpers.rb b/lib/bundler/shared_helpers.rb
index 1b703c5cbc..d259f20e6b 100644
--- a/lib/bundler/shared_helpers.rb
+++ b/lib/bundler/shared_helpers.rb
@@ -1,15 +1,15 @@
 # frozen_string_literal: true
 
-require "bundler/compatibility_guard"
+require_relative "compatibility_guard"
 
 require "pathname"
 require "rbconfig"
 require "rubygems"
 
-require "bundler/version"
-require "bundler/constants"
-require "bundler/rubygems_integration"
-require "bundler/current_ruby"
+require_relative "version"
+require_relative "constants"
+require_relative "rubygems_integration"
+require_relative "current_ruby"
 
 module Bundler
   module SharedHelpers
@@ -103,9 +103,7 @@ module Bundler
     #
     # @see {Bundler::PermissionError}
     def filesystem_access(path, action = :write, &block)
-      # Use block.call instead of yield because of a bug in Ruby 2.2.2
-      # See https://github.com/bundler/bundler/issues/5341 for details
-      block.call(path.dup.untaint)
+      yield(path.dup.untaint)
     rescue Errno::EACCES
       raise PermissionError.new(path, action)
     rescue Errno::EAGAIN
@@ -132,7 +130,7 @@ module Bundler
     def major_deprecation(major_version, message)
       bundler_major_version = Bundler.bundler_major_version
       if bundler_major_version > major_version
-        require "bundler/errors"
+        require_relative "errors"
         raise DeprecatedError, "[REMOVED] #{message}"
       end
 
@@ -289,20 +287,10 @@ module Bundler
     public :set_env
 
     def set_bundle_variables
-      begin
-        exe_file = Bundler.rubygems.bin_path("bundler", "bundle", VERSION)
-        unless File.exist?(exe_file)
-          exe_file = File.expand_path("../../../exe/bundle", __FILE__)
-        end
-        Bundler::SharedHelpers.set_env "BUNDLE_BIN_PATH", exe_file
-      rescue Gem::GemNotFoundException
-        exe_file = File.expand_path("../../../exe/bundle", __FILE__)
-        # for Ruby core repository
-        exe_file = File.expand_path("../../../../bin/bundle", __FILE__) unless File.exist?(exe_file)
-        Bundler::SharedHelpers.set_env "BUNDLE_BIN_PATH", exe_file
-      end
-
-      # Set BUNDLE_GEMFILE
+      exe_file = File.expand_path("../../../exe/bundle", __FILE__)
+      # for Ruby core repository
+      exe_file = File.expand_path("../../../../bin/bundle", __FILE__) unless File.exist?(exe_file)
+      Bundler::SharedHelpers.set_env "BUNDLE_BIN_PATH", exe_file
       Bundler::SharedHelpers.set_env "BUNDLE_GEMFILE", find_gemfile(:order_matters).to_s
       Bundler::SharedHelpers.set_env "BUNDLER_VERSION", Bundler::VERSION
     end
@@ -316,8 +304,9 @@ module Bundler
 
     def set_rubyopt
       rubyopt = [ENV["RUBYOPT"]].compact
-      return if !rubyopt.empty? && rubyopt.first =~ %r{-rbundler/setup}
-      rubyopt.unshift %(-rbundler/setup)
+      setup_require = "-r#{File.expand_path("setup", __dir__)}"
+      return if !rubyopt.empty? && rubyopt.first =~ /#{setup_require}/
+      rubyopt.unshift %(#{setup_require})
       Bundler::SharedHelpers.set_env "RUBYOPT", rubyopt.join(" ")
     end
 
@@ -351,9 +340,9 @@ module Bundler
     end
 
     def prints_major_deprecations?
-      require "bundler"
+      require_relative "../bundler"
       return false if Bundler.settings[:silence_deprecations]
-      require "bundler/deprecate"
+      require_relative "deprecate"
       return false if Bundler::Deprecate.skip
       true
     end
diff --git a/lib/bundler/source.rb b/lib/bundler/source.rb
index 26a3625bb1..4b2e305bda 100644
--- a/lib/bundler/source.rb
+++ b/lib/bundler/source.rb
@@ -2,11 +2,11 @@
 
 module Bundler
   class Source
-    autoload :Gemspec,  "bundler/source/gemspec"
-    autoload :Git,      "bundler/source/git"
-    autoload :Metadata, "bundler/source/metadata"
-    autoload :Path,     "bundler/source/path"
-    autoload :Rubygems, "bundler/source/rubygems"
+    autoload :Gemspec,  File.expand_path("source/gemspec", __dir__)
+    autoload :Git,      File.expand_path("source/git", __dir__)
+    autoload :Metadata, File.expand_path("source/metadata", __dir__)
+    autoload :Path,     File.expand_path("source/path", __dir__)
+    autoload :Rubygems, File.expand_path("source/rubygems", __dir__)
 
     attr_accessor :dependency_names
 
diff --git a/lib/bundler/source/git.rb b/lib/bundler/source/git.rb
index a8afb341d8..ed16f4a4e0 100644
--- a/lib/bundler/source/git.rb
+++ b/lib/bundler/source/git.rb
@@ -1,12 +1,12 @@
 # frozen_string_literal: true
 
-require "bundler/vendored_fileutils"
+require_relative "../vendored_fileutils"
 require "uri"
 
 module Bundler
   class Source
     class Git < Path
-      autoload :GitProxy, "bundler/source/git/git_proxy"
+      autoload :GitProxy, File.expand_path("git/git_proxy", __dir__)
 
       attr_reader :uri, :ref, :branch, :options, :submodules
 
diff --git a/lib/bundler/source/metadata.rb b/lib/bundler/source/metadata.rb
index 559b912ffd..0867879861 100644
--- a/lib/bundler/source/metadata.rb
+++ b/lib/bundler/source/metadata.rb
@@ -13,10 +13,13 @@ module Bundler
           idx << Gem::Specification.new do |s|
             s.name     = "bundler"
             s.version  = VERSION
+            s.license  = "MIT"
             s.platform = Gem::Platform::RUBY
             s.source   = self
             s.authors  = ["bundler team"]
             s.bindir   = "exe"
+            s.homepage = "https://bundler.io"
+            s.summary  = "The best way to manage your application's dependencies"
             s.executables = %w[bundle]
             # can't point to the actual gemspec or else the require paths will be wrong
             s.loaded_from = File.expand_path("..", __FILE__)
diff --git a/lib/bundler/source/path.rb b/lib/bundler/source/path.rb
index 5f3f1bc2e4..c1d25fc4da 100644
--- a/lib/bundler/source/path.rb
+++ b/lib/bundler/source/path.rb
@@ -3,7 +3,7 @@
 module Bundler
   class Source
     class Path < Source
-      autoload :Installer, "bundler/source/path/installer"
+      autoload :Installer, File.expand_path("path/installer", __dir__)
 
       attr_reader :path, :options, :root_path, :original_path
       attr_writer :name
diff --git a/lib/bundler/source/rubygems.rb b/lib/bundler/source/rubygems.rb
index 86fd329089..103faa6b80 100644
--- a/lib/bundler/source/rubygems.rb
+++ b/lib/bundler/source/rubygems.rb
@@ -6,7 +6,7 @@ require "rubygems/user_interaction"
 module Bundler
   class Source
     class Rubygems < Source
-      autoload :Remote, "bundler/source/rubygems/remote"
+      autoload :Remote, File.expand_path("rubygems/remote", __dir__)
 
       # Use the API when installing less than X gems
       API_REQUEST_LIMIT = 500
diff --git a/lib/bundler/stub_specification.rb b/lib/bundler/stub_specification.rb
index bef94b505e..bad69c9a14 100644
--- a/lib/bundler/stub_specification.rb
+++ b/lib/bundler/stub_specification.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/remote_specification"
+require_relative "remote_specification"
 
 module Bundler
   class StubSpecification < RemoteSpecification
@@ -55,8 +55,6 @@ module Bundler
       stub.full_require_paths
     end
 
-    # This is what we do in bundler/rubygems_ext
-    # full_require_paths is always implemented
     def load_paths
       full_require_paths
     end
diff --git a/lib/bundler/templates/newgem/newgem.gemspec.tt b/lib/bundler/templates/newgem/newgem.gemspec.tt
index 5505540b9e..18060942c3 100644
--- a/lib/bundler/templates/newgem/newgem.gemspec.tt
+++ b/lib/bundler/templates/newgem/newgem.gemspec.tt
@@ -1,6 +1,4 @@
-lib = File.expand_path("lib", __dir__)
-$LOAD_PATH.unshift(lib) unless $LOAD_PATH.include?(lib)
-require "<%= config[:namespaced_path] %>/version"
+require_relative 'lib/<%=config[:namespaced_path]%>/version'
 
 Gem::Specification.new do |spec|
   spec.name          = <%= config[:name].inspect %>
diff --git a/lib/bundler/ui.rb b/lib/bundler/ui.rb
index 8138b30d38..7a4fa03669 100644
--- a/lib/bundler/ui.rb
+++ b/lib/bundler/ui.rb
@@ -2,8 +2,8 @@
 
 module Bundler
   module UI
-    autoload :RGProxy, "bundler/ui/rg_proxy"
-    autoload :Shell,   "bundler/ui/shell"
-    autoload :Silent,  "bundler/ui/silent"
+    autoload :RGProxy, File.expand_path("ui/rg_proxy", __dir__)
+    autoload :Shell,   File.expand_path("ui/shell", __dir__)
+    autoload :Silent,  File.expand_path("ui/silent", __dir__)
   end
 end
diff --git a/lib/bundler/ui/rg_proxy.rb b/lib/bundler/ui/rg_proxy.rb
index e2f98481db..ef6def225b 100644
--- a/lib/bundler/ui/rg_proxy.rb
+++ b/lib/bundler/ui/rg_proxy.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/ui"
+require_relative "../ui"
 require "rubygems/user_interaction"
 
 module Bundler
diff --git a/lib/bundler/ui/shell.rb b/lib/bundler/ui/shell.rb
index 16e3d15713..8e49fa5885 100644
--- a/lib/bundler/ui/shell.rb
+++ b/lib/bundler/ui/shell.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/vendored_thor"
+require_relative "../vendored_thor"
 
 module Bundler
   module UI
@@ -35,14 +35,12 @@ module Bundler
         return if @warning_history.include? msg
         @warning_history << msg
 
-        return tell_err(msg, :yellow, newline) if Bundler.feature_flag.error_on_stderr?
-        tell_me(msg, :yellow, newline)
+        tell_err(msg, :yellow, newline)
       end
 
       def error(msg, newline = nil)
         return unless level("error")
-        return tell_err(msg, :red, newline) if Bundler.feature_flag.error_on_stderr?
-        tell_me(msg, :red, newline)
+        tell_err(msg, :red, newline)
       end
 
       def debug(msg, newline = nil)
diff --git a/lib/bundler/uri_credentials_filter.rb b/lib/bundler/uri_credentials_filter.rb
index ee3692268c..0f6ea4cefa 100644
--- a/lib/bundler/uri_credentials_filter.rb
+++ b/lib/bundler/uri_credentials_filter.rb
@@ -2,7 +2,7 @@
 
 module Bundler
   module URICredentialsFilter
-  module_function
+    module_function # rubocop:disable Layout/AccessModifierIndentation
 
     def credential_filtered_uri(uri_to_anonymize)
       return uri_to_anonymize if uri_to_anonymize.nil?
diff --git a/lib/bundler/vendor/fileutils/lib/fileutils.rb b/lib/bundler/vendor/fileutils/lib/fileutils.rb
index fb7777eb49..6fbe741498 100644
--- a/lib/bundler/vendor/fileutils/lib/fileutils.rb
+++ b/lib/bundler/vendor/fileutils/lib/fileutils.rb
@@ -6,7 +6,7 @@ rescue LoadError
   # for make mjit-headers
 end
 
-require "bundler/vendor/fileutils/lib/fileutils/version"
+require_relative "fileutils/version"
 
 #
 # = fileutils.rb
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo.rb b/lib/bundler/vendor/molinillo/lib/molinillo.rb
index 9e2867144f..baedefe98b 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo.rb
@@ -1,11 +1,11 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/compatibility'
-require 'bundler/vendor/molinillo/lib/molinillo/gem_metadata'
-require 'bundler/vendor/molinillo/lib/molinillo/errors'
-require 'bundler/vendor/molinillo/lib/molinillo/resolver'
-require 'bundler/vendor/molinillo/lib/molinillo/modules/ui'
-require 'bundler/vendor/molinillo/lib/molinillo/modules/specification_provider'
+require_relative 'molinillo/compatibility'
+require_relative 'molinillo/gem_metadata'
+require_relative 'molinillo/errors'
+require_relative 'molinillo/resolver'
+require_relative 'molinillo/modules/ui'
+require_relative 'molinillo/modules/specification_provider'
 
 # Bundler::Molinillo is a generic dependency resolution algorithm.
 module Bundler::Molinillo
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb
index 677a8bd916..31578bb5bf 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph.rb
@@ -3,8 +3,8 @@
 require 'set'
 require 'tsort'
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/log'
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/vertex'
+require_relative 'dependency_graph/log'
+require_relative 'dependency_graph/vertex'
 
 module Bundler::Molinillo
   # A directed acyclic graph that is tuned to hold named dependencies
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb
index 9849aea2fe..946a08236e 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/action'
+require_relative 'action'
 module Bundler::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_vertex.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
index 0a1e08255b..483527daf8 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_vertex.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/action'
+require_relative 'action'
 module Bundler::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/delete_edge.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/delete_edge.rb
index 1d9f4b327d..d81940585a 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/delete_edge.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/delete_edge.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/action'
+require_relative 'action'
 module Bundler::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb
index 385dcbdd06..36fce7c526 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/detach_vertex_named.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/action'
+require_relative 'action'
 module Bundler::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/log.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/log.rb
index 8582dd19c1..6f0de19886 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/log.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/log.rb
@@ -1,11 +1,11 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_edge_no_circular'
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/add_vertex'
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/delete_edge'
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/detach_vertex_named'
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/set_payload'
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/tag'
+require_relative 'add_edge_no_circular'
+require_relative 'add_vertex'
+require_relative 'delete_edge'
+require_relative 'detach_vertex_named'
+require_relative 'set_payload'
+require_relative 'tag'
 
 module Bundler::Molinillo
   class DependencyGraph
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/set_payload.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/set_payload.rb
index 37286d104a..2e9b90e6cd 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/set_payload.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/set_payload.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/action'
+require_relative 'action'
 module Bundler::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/tag.rb b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/tag.rb
index d6ad16e07a..fccfc78cc7 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/tag.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/dependency_graph/tag.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph/action'
+require_relative 'action'
 module Bundler::Molinillo
   class DependencyGraph
     # @!visibility private
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb b/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb
index ce0931f103..89c7c324d5 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/errors.rb
@@ -80,7 +80,7 @@ module Bundler::Molinillo
       @specification_provider = specification_provider
     end
 
-    require 'bundler/vendor/molinillo/lib/molinillo/delegates/specification_provider'
+    require_relative 'delegates/specification_provider'
     include Delegates::SpecificationProvider
 
     # @return [String] An error message that includes requirement trees,
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb b/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb
index 0eb665d17a..acf7777414 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/resolution.rb
@@ -238,11 +238,11 @@ module Bundler::Molinillo
         debug { 'Activated: ' + Hash[activated.vertices.select { |_n, v| v.payload }].keys.join(', ') } if state
       end
 
-      require 'bundler/vendor/molinillo/lib/molinillo/state'
-      require 'bundler/vendor/molinillo/lib/molinillo/modules/specification_provider'
+      require_relative 'state'
+      require_relative 'modules/specification_provider'
 
-      require 'bundler/vendor/molinillo/lib/molinillo/delegates/resolution_state'
-      require 'bundler/vendor/molinillo/lib/molinillo/delegates/specification_provider'
+      require_relative 'delegates/resolution_state'
+      require_relative 'delegates/specification_provider'
 
       include Bundler::Molinillo::Delegates::ResolutionState
       include Bundler::Molinillo::Delegates::SpecificationProvider
diff --git a/lib/bundler/vendor/molinillo/lib/molinillo/resolver.rb b/lib/bundler/vendor/molinillo/lib/molinillo/resolver.rb
index 7d36858778..95eaab5991 100644
--- a/lib/bundler/vendor/molinillo/lib/molinillo/resolver.rb
+++ b/lib/bundler/vendor/molinillo/lib/molinillo/resolver.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require 'bundler/vendor/molinillo/lib/molinillo/dependency_graph'
+require_relative 'dependency_graph'
 
 module Bundler::Molinillo
   # This class encapsulates a dependency resolver.
@@ -9,7 +9,7 @@ module Bundler::Molinillo
   #
   #
   class Resolver
-    require 'bundler/vendor/molinillo/lib/molinillo/resolution'
+    require_relative 'resolution'
 
     # @return [SpecificationProvider] the specification provider used
     #   in the resolution process
diff --git a/lib/bundler/vendor/thor/lib/thor/base.rb b/lib/bundler/vendor/thor/lib/thor/base.rb
index e79d03d087..f55b14fbfc 100644
--- a/lib/bundler/vendor/thor/lib/thor/base.rb
+++ b/lib/bundler/vendor/thor/lib/thor/base.rb
@@ -9,9 +9,9 @@ require "bundler/vendor/thor/lib/thor/line_editor"
 require "bundler/vendor/thor/lib/thor/util"
 
 class Bundler::Thor
-  autoload :Actions,    "bundler/vendor/thor/lib/thor/actions"
-  autoload :RakeCompat, "bundler/vendor/thor/lib/thor/rake_compat"
-  autoload :Group,      "bundler/vendor/thor/lib/thor/group"
+  autoload :Actions,    File.expand_path("actions", __dir__)
+  autoload :RakeCompat, File.expand_path("rake_compat", __dir__)
+  autoload :Group,      File.expand_path("group", __dir__)
 
   # Shortcuts for help.
   HELP_MAPPINGS       = %w(-h -? --help -D)
diff --git a/lib/bundler/vendor/thor/lib/thor/shell.rb b/lib/bundler/vendor/thor/lib/thor/shell.rb
index a68cdf8a98..e36fa472d6 100644
--- a/lib/bundler/vendor/thor/lib/thor/shell.rb
+++ b/lib/bundler/vendor/thor/lib/thor/shell.rb
@@ -24,9 +24,9 @@ class Bundler::Thor
     SHELL_DELEGATED_METHODS = [:ask, :error, :set_color, :yes?, :no?, :say, :say_status, :print_in_columns, :print_table, :print_wrapped, :file_collision, :terminal_width]
     attr_writer :shell
 
-    autoload :Basic, "bundler/vendor/thor/lib/thor/shell/basic"
-    autoload :Color, "bundler/vendor/thor/lib/thor/shell/color"
-    autoload :HTML,  "bundler/vendor/thor/lib/thor/shell/html"
+    autoload :Basic, File.expand_path("shell/basic", __dir__)
+    autoload :Color, File.expand_path("shell/color", __dir__)
+    autoload :HTML,  File.expand_path("shell/html", __dir__)
 
     # Add shell to initialize config values.
     #
diff --git a/lib/bundler/vendored_fileutils.rb b/lib/bundler/vendored_fileutils.rb
index d14e98baf7..4b71759224 100644
--- a/lib/bundler/vendored_fileutils.rb
+++ b/lib/bundler/vendored_fileutils.rb
@@ -2,7 +2,7 @@
 
 module Bundler; end
 if RUBY_VERSION >= "2.4"
-  require "bundler/vendor/fileutils/lib/fileutils"
+  require_relative "vendor/fileutils/lib/fileutils"
 else
   # the version we vendor is 2.4+
   require "fileutils"
diff --git a/lib/bundler/vendored_molinillo.rb b/lib/bundler/vendored_molinillo.rb
index 061b634f72..d1976f5cb4 100644
--- a/lib/bundler/vendored_molinillo.rb
+++ b/lib/bundler/vendored_molinillo.rb
@@ -1,4 +1,4 @@
 # frozen_string_literal: true
 
 module Bundler; end
-require "bundler/vendor/molinillo/lib/molinillo"
+require_relative "vendor/molinillo/lib/molinillo"
diff --git a/lib/bundler/vendored_persistent.rb b/lib/bundler/vendored_persistent.rb
index de9c42fcc1..7670b83992 100644
--- a/lib/bundler/vendored_persistent.rb
+++ b/lib/bundler/vendored_persistent.rb
@@ -15,7 +15,7 @@ module Bundler
     end
   end
 end
-require "bundler/vendor/net-http-persistent/lib/net/http/persistent"
+require_relative "vendor/net-http-persistent/lib/net/http/persistent"
 
 module Bundler
   class PersistentHTTP < Persistent::Net::HTTP::Persistent
diff --git a/lib/bundler/vendored_thor.rb b/lib/bundler/vendored_thor.rb
index 8cca090f55..b0b7e7be84 100644
--- a/lib/bundler/vendored_thor.rb
+++ b/lib/bundler/vendored_thor.rb
@@ -5,4 +5,4 @@ module Bundler
     Kernel.send(:require, "bundler/vendor/thor/lib/thor/actions")
   end
 end
-require "bundler/vendor/thor/lib/thor"
+require_relative "vendor/thor/lib/thor"
diff --git a/lib/bundler/version.rb b/lib/bundler/version.rb
index cfd6300950..21eeeb0fd4 100644
--- a/lib/bundler/version.rb
+++ b/lib/bundler/version.rb
@@ -1,23 +1,7 @@
 # frozen_string_literal: false
 
 module Bundler
-  # We're doing this because we might write tests that deal
-  # with other versions of bundler and we are unsure how to
-  # handle this better.
-  VERSION = "2.1.0.pre.1".freeze unless defined?(::Bundler::VERSION)
-
-  def self.overwrite_loaded_gem_version
-    begin
-      require "rubygems"
-    rescue LoadError
-      return
-    end
-    return unless bundler_spec = Gem.loaded_specs["bundler"]
-    return if bundler_spec.version == VERSION
-    bundler_spec.version = Bundler::VERSION
-  end
-  private_class_method :overwrite_loaded_gem_version
-  overwrite_loaded_gem_version
+  VERSION = "2.1.0.pre.1".freeze
 
   def self.bundler_major_version
     @bundler_major_version ||= VERSION.split(".").first.to_i
diff --git a/lib/bundler/vlad.rb b/lib/bundler/vlad.rb
index 68181e7db8..538e8c3e74 100644
--- a/lib/bundler/vlad.rb
+++ b/lib/bundler/vlad.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "bundler/shared_helpers"
+require_relative "shared_helpers"
 Bundler::SharedHelpers.major_deprecation 2,
   "The Bundler task for Vlad"
 
@@ -8,7 +8,7 @@ Bundler::SharedHelpers.major_deprecation 2,
 #
 # Add "require 'bundler/vlad'" in your Vlad deploy.rb, and
 # include the vlad:bundle:install task in your vlad:deploy task.
-require "bundler/deployment"
+require_relative "deployment"
 
 include Rake::DSL if defined? Rake::DSL
 
diff --git a/lib/bundler/yaml_serializer.rb b/lib/bundler/yaml_serializer.rb
index 374b3bb5e3..1965853931 100644
--- a/lib/bundler/yaml_serializer.rb
+++ b/lib/bundler/yaml_serializer.rb
@@ -3,7 +3,7 @@
 module Bundler
   # A stub yaml serializer that can handle only hashes and strings (as of now).
   module YAMLSerializer
-  module_function
+    module_function # rubocop:disable Layout/AccessModifierIndentation
 
     def dump(hash)
       yaml = String.new("---")