Merge RubyGems-3.3.0 and Bundler-2.3.0

26 files changed, 278 insertions, 174 deletions

diff --git a/lib/bundler.rb b/lib/bundler.rb
index 81dfd05d26..89865a8254 100644
--- a/lib/bundler.rb
+++ b/lib/bundler.rb
@@ -66,6 +66,7 @@ module Bundler
   autoload :RubyDsl,                File.expand_path("bundler/ruby_dsl", __dir__)
   autoload :RubyVersion,            File.expand_path("bundler/ruby_version", __dir__)
   autoload :Runtime,                File.expand_path("bundler/runtime", __dir__)
+  autoload :SelfManager,            File.expand_path("bundler/self_manager", __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__)
@@ -643,6 +644,13 @@ EOF
       Bundler.rubygems.clear_paths
     end
 
+    def self_manager
+      @self_manager ||= begin
+                          require_relative "bundler/self_manager"
+                          Bundler::SelfManager.new
+                        end
+    end
+
     private
 
     def eval_yaml_gemspec(path, contents)
diff --git a/lib/bundler/cli.rb b/lib/bundler/cli.rb
index 36d0472c62..f6e20e7c67 100644
--- a/lib/bundler/cli.rb
+++ b/lib/bundler/cli.rb
@@ -61,6 +61,8 @@ module Bundler
         Bundler.reset_settings_and_root!
       end
 
+      Bundler.self_manager.restart_with_locked_bundler_if_needed
+
       Bundler.settings.set_command_option_if_given :retry, options[:retry]
 
       current_cmd = args.last[:current_command].name
diff --git a/lib/bundler/cli/install.rb b/lib/bundler/cli/install.rb
index 4c1915fea6..85f702bc64 100644
--- a/lib/bundler/cli/install.rb
+++ b/lib/bundler/cli/install.rb
@@ -12,6 +12,8 @@ module Bundler
 
       warn_if_root
 
+      Bundler.self_manager.install_locked_bundler_and_restart_with_it_if_needed
+
       Bundler::SharedHelpers.set_env "RB_USER_INSTALL", "1" if Bundler::FREEBSD
 
       # Disable color in deployment mode
diff --git a/lib/bundler/definition.rb b/lib/bundler/definition.rb
index 84f0367ac7..9a94bd3ed3 100644
--- a/lib/bundler/definition.rb
+++ b/lib/bundler/definition.rb
@@ -294,7 +294,7 @@ module Bundler
 
         if updating_major = locked_major < current_major
           Bundler.ui.warn "Warning: the lockfile is being updated to Bundler #{current_major}, " \
-                          "after which you will be unable to return to Bundler #{@locked_bundler_version.segments.first}."
+                          "after which you will be unable to return to Bundler #{locked_major}."
         end
       end
 
diff --git a/lib/bundler/fetcher.rb b/lib/bundler/fetcher.rb
index 6dd6d089eb..a453157e68 100644
--- a/lib/bundler/fetcher.rb
+++ b/lib/bundler/fetcher.rb
@@ -122,7 +122,6 @@ module Bundler
 
     # return the specs in the bundler format as an index
     def specs(gem_names, source)
-      old = Bundler.rubygems.sources
       index = Bundler::Index.new
 
       if Bundler::Fetcher.disable_endpoint
@@ -153,8 +152,6 @@ module Bundler
     rescue CertificateFailureError
       Bundler.ui.info "" if gem_names && use_api # newline after dots
       raise
-    ensure
-      Bundler.rubygems.sources = old
     end
 
     def use_api
diff --git a/lib/bundler/installer.rb b/lib/bundler/installer.rb
index 49ff177c0f..61bf1e06d4 100644
--- a/lib/bundler/installer.rb
+++ b/lib/bundler/installer.rb
@@ -239,7 +239,7 @@ module Bundler
 
     def ensure_specs_are_compatible!
       system_ruby = Bundler::RubyVersion.system
-      rubygems_version = Gem::Version.create(Gem::VERSION)
+      rubygems_version = Bundler.rubygems.version
       @definition.specs.each do |spec|
         if required_ruby_version = spec.required_ruby_version
           unless required_ruby_version.satisfied_by?(system_ruby.gem_version)
diff --git a/lib/bundler/lockfile_parser.rb b/lib/bundler/lockfile_parser.rb
index 6ff4910a36..e074cbfc33 100644
--- a/lib/bundler/lockfile_parser.rb
+++ b/lib/bundler/lockfile_parser.rb
@@ -46,6 +46,16 @@ module Bundler
       attributes
     end
 
+    def self.bundled_with
+      lockfile = Bundler.default_lockfile
+      return unless lockfile.file?
+
+      lockfile_contents = Bundler.read_file(lockfile)
+      return unless lockfile_contents.include?(BUNDLED)
+
+      lockfile_contents.split(BUNDLED).last.strip
+    end
+
     def initialize(lockfile)
       @platforms    = []
       @sources      = []
@@ -77,25 +87,12 @@ module Bundler
         end
       end
       @specs = @specs.values.sort_by(&:identifier)
-      warn_for_outdated_bundler_version
     rescue ArgumentError => e
       Bundler.ui.debug(e)
       raise LockfileError, "Your lockfile is unreadable. Run `rm #{Bundler.default_lockfile.relative_path_from(SharedHelpers.pwd)}` " \
         "and then `bundle install` to generate a new lockfile."
     end
 
-    def warn_for_outdated_bundler_version
-      return unless bundler_version
-      return if bundler_version.segments.last == "dev"
-      prerelease_text = bundler_version.prerelease? ? " --pre" : ""
-      current_version = Gem::Version.create(Bundler::VERSION)
-      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
 
     TYPES = {
diff --git a/lib/bundler/plugin/installer.rb b/lib/bundler/plugin/installer.rb
index d7411fff45..81ecafa470 100644
--- a/lib/bundler/plugin/installer.rb
+++ b/lib/bundler/plugin/installer.rb
@@ -21,7 +21,7 @@ module Bundler
         elsif options[:local_git]
           install_local_git(names, version, options)
         else
-          sources = options[:source] || Bundler.rubygems.sources
+          sources = options[:source] || Gem.sources
           install_rubygems(names, version, sources)
         end
       end
diff --git a/lib/bundler/rubygems_integration.rb b/lib/bundler/rubygems_integration.rb
index effb88c1cd..785f7fa360 100644
--- a/lib/bundler/rubygems_integration.rb
+++ b/lib/bundler/rubygems_integration.rb
@@ -12,25 +12,21 @@ module Bundler
       EXT_LOCK = Monitor.new
     end
 
-    def self.version
-      @version ||= Gem::Version.new(Gem::VERSION)
-    end
-
-    def self.provides?(req_str)
-      Gem::Requirement.new(req_str).satisfied_by?(version)
-    end
-
     def initialize
       @replaced_methods = {}
       backport_ext_builder_monitor
     end
 
     def version
-      self.class.version
+      @version ||= Gem.rubygems_version
     end
 
     def provides?(req_str)
-      self.class.provides?(req_str)
+      Gem::Requirement.new(req_str).satisfied_by?(version)
+    end
+
+    def supports_bundler_trampolining?
+      provides?(">= 3.3.0.a")
     end
 
     def build_args
@@ -142,19 +138,6 @@ module Bundler
       end
     end
 
-    def sources=(val)
-      # Gem.configuration creates a new Gem::ConfigFile, which by default will read ~/.gemrc
-      # If that file exists, its settings (including sources) will overwrite the values we
-      # are about to set here. In order to avoid that, we force memoizing the config file now.
-      configuration
-
-      Gem.sources = val
-    end
-
-    def sources
-      Gem.sources
-    end
-
     def gem_dir
       Gem.dir
     end
@@ -588,6 +571,10 @@ module Bundler
       end
     end
 
+    def find_bundler(version)
+      find_name("bundler").find {|s| s.version.to_s == version }
+    end
+
     def find_name(name)
       Gem::Specification.stubs_for(name).map(&:to_spec)
     end
diff --git a/lib/bundler/self_manager.rb b/lib/bundler/self_manager.rb
new file mode 100644
index 0000000000..bda2eb51f3
--- /dev/null
+++ b/lib/bundler/self_manager.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+module Bundler
+  #
+  # This class handles installing and switching to the version of bundler needed
+  # by an application.
+  #
+  class SelfManager
+    def restart_with_locked_bundler_if_needed
+      return unless needs_switching? && installed?
+
+      restart_with_locked_bundler
+    end
+
+    def install_locked_bundler_and_restart_with_it_if_needed
+      return unless needs_switching?
+
+      Bundler.ui.info \
+        "Bundler #{current_version} is running, but your lockfile was generated with #{lockfile_version}. " \
+        "Installing Bundler #{lockfile_version} and restarting using that version."
+
+      install_and_restart_with_locked_bundler
+    end
+
+    private
+
+    def install_and_restart_with_locked_bundler
+      bundler_dep = Gem::Dependency.new("bundler", lockfile_version)
+
+      Gem.install(bundler_dep)
+    rescue StandardError => e
+      Bundler.ui.trace e
+      Bundler.ui.warn "There was an error installing the locked bundler version (#{lockfile_version}), rerun with the `--verbose` flag for more details. Going on using bundler #{current_version}."
+    else
+      restart_with_locked_bundler
+    end
+
+    def restart_with_locked_bundler
+      configured_gem_home = ENV["GEM_HOME"]
+      configured_gem_path = ENV["GEM_PATH"]
+
+      Bundler.with_original_env do
+        Kernel.exec(
+          { "GEM_HOME" => configured_gem_home, "GEM_PATH" => configured_gem_path, "BUNDLER_VERSION" => lockfile_version },
+          $PROGRAM_NAME, *ARGV
+        )
+      end
+    end
+
+    def needs_switching?
+      ENV["BUNDLER_VERSION"].nil? &&
+        Bundler.rubygems.supports_bundler_trampolining? &&
+        SharedHelpers.in_bundle? &&
+        lockfile_version &&
+        !lockfile_version.end_with?(".dev") &&
+        lockfile_version != current_version
+    end
+
+    def installed?
+      Bundler.configure
+
+      Bundler.rubygems.find_bundler(lockfile_version)
+    end
+
+    def current_version
+      @current_version ||= Bundler::VERSION
+    end
+
+    def lockfile_version
+      @lockfile_version ||= Bundler::LockfileParser.bundled_with
+    end
+  end
+end
diff --git a/lib/bundler/source/metadata.rb b/lib/bundler/source/metadata.rb
index 50b65ce0ea..8bdbaa5527 100644
--- a/lib/bundler/source/metadata.rb
+++ b/lib/bundler/source/metadata.rb
@@ -25,7 +25,7 @@ module Bundler
             s.loaded_from = File.expand_path("..", __FILE__)
           end
 
-          if local_spec = Bundler.rubygems.find_name("bundler").find {|s| s.version.to_s == VERSION }
+          if local_spec = Bundler.rubygems.find_bundler(VERSION)
             idx << local_spec
           end
 
diff --git a/lib/bundler/templates/Executable.bundler b/lib/bundler/templates/Executable.bundler
index 8009412ea2..6bb5c51090 100644
--- a/lib/bundler/templates/Executable.bundler
+++ b/lib/bundler/templates/Executable.bundler
@@ -73,7 +73,7 @@ m = Module.new do
 
     requirement = bundler_gem_version.approximate_recommendation
 
-    return requirement unless Gem::Version.new(Gem::VERSION) < Gem::Version.new("2.7.0")
+    return requirement unless Gem.rubygems_version < Gem::Version.new("2.7.0")
 
     requirement += ".a" if bundler_gem_version.prerelease?
 
diff --git a/lib/bundler/version.rb b/lib/bundler/version.rb
index 0c0d9d360d..d987722f78 100644
--- a/lib/bundler/version.rb
+++ b/lib/bundler/version.rb
@@ -1,7 +1,7 @@
 # frozen_string_literal: false
 
 module Bundler
-  VERSION = "2.3.0.dev".freeze
+  VERSION = "2.3.0".freeze
 
   def self.bundler_major_version
     @bundler_major_version ||= VERSION.split(".").first.to_i
diff --git a/lib/rubygems.rb b/lib/rubygems.rb
index 40f3a893d8..a956e06bdb 100644
--- a/lib/rubygems.rb
+++ b/lib/rubygems.rb
@@ -8,7 +8,7 @@
 require 'rbconfig'
 
 module Gem
-  VERSION = "3.3.0.dev".freeze
+  VERSION = "3.3.0".freeze
 end
 
 # Must be first since it unloads the prelude from 1.9.2
diff --git a/spec/bundler/bundler/plugin/installer_spec.rb b/spec/bundler/bundler/plugin/installer_spec.rb
index e89720f6f7..2c50ee5afc 100644
--- a/spec/bundler/bundler/plugin/installer_spec.rb
+++ b/spec/bundler/bundler/plugin/installer_spec.rb
@@ -7,7 +7,7 @@ RSpec.describe Bundler::Plugin::Installer do
     it "uses Gem.sources when non of the source is provided" do
       sources = double(:sources)
       Bundler.settings # initialize it before we have to touch rubygems.ext_lock
-      allow(Bundler).to receive_message_chain("rubygems.sources") { sources }
+      allow(Gem).to receive(:sources) { sources }
 
       allow(installer).to receive(:install_rubygems).
         with("new-plugin", [">= 0"], sources).once
diff --git a/spec/bundler/commands/binstubs_spec.rb b/spec/bundler/commands/binstubs_spec.rb
index 1cd0e16d95..ceef07d36b 100644
--- a/spec/bundler/commands/binstubs_spec.rb
+++ b/spec/bundler/commands/binstubs_spec.rb
@@ -186,11 +186,25 @@ RSpec.describe "bundle binstubs <gem>" do
 
           before do
             lockfile lockfile.gsub(/BUNDLED WITH\n   .*$/m, "BUNDLED WITH\n   55.0")
+
+            update_repo2 do
+              with_built_bundler("55.0") {|gem_path| FileUtils.mv(gem_path, gem_repo2("gems")) }
+            end
+          end
+
+          it "installs and runs the exact version of bundler", :rubygems => ">= 3.3.0.dev" do
+            sys_exec "bin/bundle install --verbose", :env => { "BUNDLER_SPEC_GEM_SOURCES" => file_uri_for(gem_repo2).to_s, "RUBYOPT" => "-r#{spec_dir}/support/hax.rb" }
+            expect(exitstatus).not_to eq(42)
+            expect(out).to include("Bundler 55.1 is running, but your lockfile was generated with 55.0. Installing Bundler 55.0 and restarting using that version.")
+            expect(out).to include("Using bundler 55.0")
+            expect(err).not_to include("Activating bundler (~> 55.0) failed:")
           end
 
-          it "runs the available version of bundler when the version is older and the same major" do
-            sys_exec "bin/bundle install"
+          it "runs the available version of bundler", :rubygems => "< 3.3.0.dev" do
+            sys_exec "bin/bundle install --verbose"
             expect(exitstatus).not_to eq(42)
+            expect(out).not_to include("Bundler 55.1 is running, but your lockfile was generated with 55.0. Installing Bundler 55.0 and restarting using that version.")
+            expect(out).to include("Using bundler 55.1")
             expect(err).not_to include("Activating bundler (~> 55.0) failed:")
           end
         end
diff --git a/spec/bundler/commands/check_spec.rb b/spec/bundler/commands/check_spec.rb
index 1fa35136eb..e0c9a04c25 100644
--- a/spec/bundler/commands/check_spec.rb
+++ b/spec/bundler/commands/check_spec.rb
@@ -471,10 +471,10 @@ RSpec.describe "bundle check" do
     end
 
     context "is newer" do
-      it "does not change the lock but warns" do
+      it "does not change the lock and does not warn" do
         lockfile lock_with(Bundler::VERSION.succ)
         bundle :check
-        expect(err).to include("the running version of Bundler (#{Bundler::VERSION}) is older than the version that created the lockfile (#{Bundler::VERSION.succ})")
+        expect(err).to be_empty
         expect(lockfile).to eq lock_with(Bundler::VERSION.succ)
       end
     end
diff --git a/spec/bundler/lock/lockfile_spec.rb b/spec/bundler/lock/lockfile_spec.rb
index 8befb0d400..a2a50d4cf0 100644
--- a/spec/bundler/lock/lockfile_spec.rb
+++ b/spec/bundler/lock/lockfile_spec.rb
@@ -39,7 +39,7 @@ RSpec.describe "the lockfile format" do
     G
   end
 
-  it "updates the lockfile's bundler version if current ver. is newer" do
+  it "updates the lockfile's bundler version if current ver. is newer, and version was forced through BUNDLER_VERSION" do
     system_gems "bundler-1.8.2"
 
     lockfile <<-L
@@ -64,12 +64,15 @@ RSpec.describe "the lockfile format" do
          1.8.2
     L
 
-    install_gemfile <<-G, :env => { "BUNDLER_VERSION" => Bundler::VERSION }
+    install_gemfile <<-G, :verbose => true, :env => { "BUNDLER_VERSION" => Bundler::VERSION }
       source "#{file_uri_for(gem_repo2)}"
 
       gem "rack"
     G
 
+    expect(out).not_to include("Bundler #{Bundler::VERSION} is running, but your lockfile was generated with 1.8.2.")
+    expect(out).to include("Using bundler #{Bundler::VERSION}")
+
     expect(lockfile).to eq <<~G
       GEM
         remote: #{file_uri_for(gem_repo2)}/
@@ -87,9 +90,13 @@ RSpec.describe "the lockfile format" do
     G
   end
 
-  it "does not update the lockfile's bundler version if nothing changed during bundle install" do
+  it "does not update the lockfile's bundler version if nothing changed during bundle install, but uses the locked version", :rubygems => ">= 3.3.0.a" do
     version = "#{Bundler::VERSION.split(".").first}.0.0.a"
 
+    update_repo2 do
+      with_built_bundler(version) {|gem_path| FileUtils.mv(gem_path, gem_repo2("gems")) }
+    end
+
     lockfile <<-L
       GEM
         remote: #{file_uri_for(gem_repo2)}/
@@ -106,12 +113,15 @@ RSpec.describe "the lockfile format" do
          #{version}
     L
 
-    install_gemfile <<-G
+    install_gemfile <<-G, :verbose => true, :env => { "BUNDLER_SPEC_GEM_SOURCES" => file_uri_for(gem_repo2).to_s }
       source "#{file_uri_for(gem_repo2)}"
 
       gem "rack"
     G
 
+    expect(out).to include("Bundler #{Bundler::VERSION} is running, but your lockfile was generated with #{version}.")
+    expect(out).to include("Using bundler #{version}")
+
     expect(lockfile).to eq <<~G
       GEM
         remote: #{file_uri_for(gem_repo2)}/
@@ -129,97 +139,12 @@ RSpec.describe "the lockfile format" do
     G
   end
 
-  it "updates the lockfile's bundler version if not present" do
-    lockfile <<-L
-      GEM
-        remote: #{file_uri_for(gem_repo2)}/
-        specs:
-          rack (1.0.0)
-
-      PLATFORMS
-        #{lockfile_platforms}
-
-      DEPENDENCIES
-        rack
-    L
-
-    install_gemfile <<-G
-      source "#{file_uri_for(gem_repo2)}"
-
-      gem "rack", "> 0"
-    G
-
-    expect(lockfile).to eq <<~G
-      GEM
-        remote: #{file_uri_for(gem_repo2)}/
-        specs:
-          rack (1.0.0)
-
-      PLATFORMS
-        #{lockfile_platforms}
-
-      DEPENDENCIES
-        rack (> 0)
-
-      BUNDLED WITH
-         #{Bundler::VERSION}
-    G
-  end
-
-  it "warns if the current version is older than lockfile's bundler version, and locked version is a final release" do
-    current_version = "999.998.999"
-    system_gems "bundler-#{current_version}"
-    newer_minor = "999.999.0"
-
-    lockfile <<-L
-      GEM
-        remote: #{file_uri_for(gem_repo2)}/
-        specs:
-          rack (1.0.0)
-
-      PLATFORMS
-        #{lockfile_platforms}
-
-      DEPENDENCIES
-        rack
-
-      BUNDLED WITH
-         #{newer_minor}
-    L
-
-    install_gemfile <<-G, :env => { "BUNDLER_VERSION" => current_version }
-      source "#{file_uri_for(gem_repo2)}"
-
-      gem "rack"
-    G
-
-    warning_message = "the running version of Bundler (#{current_version}) is older " \
-                      "than the version that created the lockfile (#{newer_minor}). " \
-                      "We suggest you to upgrade to the version that created the " \
-                      "lockfile by running `gem install bundler:#{newer_minor}`."
-    expect(err).to include warning_message
-
-    expect(lockfile).to eq <<~G
-      GEM
-        remote: #{file_uri_for(gem_repo2)}/
-        specs:
-          rack (1.0.0)
-
-      PLATFORMS
-        #{lockfile_platforms}
-
-      DEPENDENCIES
-        rack
-
-      BUNDLED WITH
-         #{newer_minor}
-    G
-  end
+  it "does not update the lockfile's bundler version if nothing changed during bundle install, and uses the latest version", :rubygems => "< 3.3.0.a" do
+    version = "#{Bundler::VERSION.split(".").first}.0.0.a"
 
-  it "warns if the current version is older than lockfile's bundler version, and locked version is a prerelease" do
-    current_version = "999.998.999"
-    system_gems "bundler-#{current_version}"
-    newer_minor = "999.999.0.pre1"
+    update_repo2 do
+      with_built_bundler(version) {|gem_path| FileUtils.mv(gem_path, gem_repo2("gems")) }
+    end
 
     lockfile <<-L
       GEM
@@ -234,20 +159,17 @@ RSpec.describe "the lockfile format" do
         rack
 
       BUNDLED WITH
-         #{newer_minor}
+         #{version}
     L
 
-    install_gemfile <<-G, :env => { "BUNDLER_VERSION" => current_version }
+    install_gemfile <<-G, :verbose => true, :env => { "BUNDLER_SPEC_GEM_SOURCES" => file_uri_for(gem_repo2).to_s }
       source "#{file_uri_for(gem_repo2)}"
 
       gem "rack"
     G
 
-    warning_message = "the running version of Bundler (#{current_version}) is older " \
-                      "than the version that created the lockfile (#{newer_minor}). " \
-                      "We suggest you to upgrade to the version that created the " \
-                      "lockfile by running `gem install bundler:#{newer_minor} --pre`."
-    expect(err).to include warning_message
+    expect(out).not_to include("Bundler #{Bundler::VERSION} is running, but your lockfile was generated with #{version}.")
+    expect(out).to include("Using bundler #{Bundler::VERSION}")
 
     expect(lockfile).to eq <<~G
       GEM
@@ -262,15 +184,11 @@ RSpec.describe "the lockfile format" do
         rack
 
       BUNDLED WITH
-         #{newer_minor}
+         #{version}
     G
   end
 
-  it "doesn't warn if the current version is older than lockfile's bundler version, and locked version is a dev version" do
-    current_version = "999.998.999"
-    system_gems "bundler-#{current_version}"
-    newer_minor = "999.999.0.dev"
-
+  it "adds the BUNDLED WITH section if not present" do
     lockfile <<-L
       GEM
         remote: #{file_uri_for(gem_repo2)}/
@@ -282,19 +200,14 @@ RSpec.describe "the lockfile format" do
 
       DEPENDENCIES
         rack
-
-      BUNDLED WITH
-         #{newer_minor}
     L
 
-    install_gemfile <<-G, :env => { "BUNDLER_VERSION" => current_version }
+    install_gemfile <<-G
       source "#{file_uri_for(gem_repo2)}"
 
-      gem "rack"
+      gem "rack", "> 0"
     G
 
-    expect(err).to be_empty
-
     expect(lockfile).to eq <<~G
       GEM
         remote: #{file_uri_for(gem_repo2)}/
@@ -305,10 +218,10 @@ RSpec.describe "the lockfile format" do
         #{lockfile_platforms}
 
       DEPENDENCIES
-        rack
+        rack (> 0)
 
       BUNDLED WITH
-         #{newer_minor}
+         #{Bundler::VERSION}
     G
   end
 
diff --git a/spec/bundler/runtime/platform_spec.rb b/spec/bundler/runtime/platform_spec.rb
index 433396d106..b937de8059 100644
--- a/spec/bundler/runtime/platform_spec.rb
+++ b/spec/bundler/runtime/platform_spec.rb
@@ -168,7 +168,7 @@ RSpec.describe "Bundler.setup with multi platform stuff" do
         nokogiri
 
       BUNDLED WITH
-        2.1.4
+        #{Bundler::VERSION}
     G
 
     bundle "install"
diff --git a/spec/bundler/runtime/self_management_spec.rb b/spec/bundler/runtime/self_management_spec.rb
new file mode 100644
index 0000000000..def9361d0f
--- /dev/null
+++ b/spec/bundler/runtime/self_management_spec.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+RSpec.describe "Self management", :rubygems => ">= 3.3.0.dev" do
+  describe "auto switching" do
+    let(:next_minor) do
+      Bundler::VERSION.split(".").map.with_index {|s, i| i == 1 ? s.to_i + 1 : s }[0..2].join(".")
+    end
+
+    before do
+      build_repo2 do
+        with_built_bundler(next_minor) {|gem_path| FileUtils.mv(gem_path, gem_repo2("gems")) }
+      end
+
+      gemfile <<-G
+        source "#{file_uri_for(gem_repo2)}"
+
+        gem "rack"
+      G
+    end
+
+    it "installs locked version when using system path and uses it" do
+      lockfile_bundled_with(next_minor)
+
+      bundle "config set --local path.system true"
+      bundle "install", :env => { "BUNDLER_SPEC_GEM_SOURCES" => file_uri_for(gem_repo2).to_s }
+      expect(out).to include("Bundler #{Bundler::VERSION} is running, but your lockfile was generated with #{next_minor}. Installing Bundler #{next_minor} and restarting using that version.")
+
+      # It uninstalls the older system bundler
+      bundle "clean --force"
+      expect(out).to eq("Removing bundler (#{Bundler::VERSION})")
+
+      # App now uses locked version
+      bundle "-v"
+      expect(out).to end_with(next_minor[0] == "2" ? "Bundler version #{next_minor}" : next_minor)
+
+      # Subsequent installs use the locked version without reinstalling
+      bundle "install --verbose"
+      expect(out).to include("Using bundler #{next_minor}")
+      expect(out).not_to include("Bundler #{Bundler::VERSION} is running, but your lockfile was generated with #{next_minor}. Installing Bundler #{next_minor} and restarting using that version.")
+    end
+
+    it "installs locked version when using local path and uses it" do
+      lockfile_bundled_with(next_minor)
+
+      bundle "config set --local path vendor/bundle"
+      bundle "install", :env => { "BUNDLER_SPEC_GEM_SOURCES" => file_uri_for(gem_repo2).to_s }
+      expect(out).to include("Bundler #{Bundler::VERSION} is running, but your lockfile was generated with #{next_minor}. Installing Bundler #{next_minor} and restarting using that version.")
+
+      # It does not uninstall the locked bundler
+      bundle "clean"
+      expect(out).to be_empty
+
+      # App now uses locked version
+      bundle "-v"
+      expect(out).to end_with(next_minor[0] == "2" ? "Bundler version #{next_minor}" : next_minor)
+
+      # Subsequent installs use the locked version without reinstalling
+      bundle "install --verbose"
+      expect(out).to include("Using bundler #{next_minor}")
+      expect(out).not_to include("Bundler #{Bundler::VERSION} is running, but your lockfile was generated with #{next_minor}. Installing Bundler #{next_minor} and restarting using that version.")
+    end
+
+    it "does not try to install a development version" do
+      lockfile_bundled_with("#{next_minor}.dev")
+
+      bundle "install --verbose"
+      expect(out).not_to match(/restarting using that version/)
+
+      bundle "-v"
+      expect(out).to eq(Bundler::VERSION[0] == "2" ? "Bundler version #{Bundler::VERSION}" : Bundler::VERSION)
+    end
+
+    it "shows a discreet message if locked bundler does not exist, and something more complete in `--verbose` mode" do
+      missing_minor ="#{Bundler::VERSION[0]}.999.999"
+
+      lockfile_bundled_with(missing_minor)
+
+      bundle "install"
+      expect(err).to eq("There was an error installing the locked bundler version (#{missing_minor}), rerun with the `--verbose` flag for more details. Going on using bundler #{Bundler::VERSION}.")
+
+      bundle "install --verbose"
+      expect(err).to include("There was an error installing the locked bundler version (#{missing_minor}), rerun with the `--verbose` flag for more details. Going on using bundler #{Bundler::VERSION}.")
+      expect(err).to include("Gem::UnsatisfiableDependencyError")
+
+      bundle "-v"
+      expect(out).to eq(Bundler::VERSION[0] == "2" ? "Bundler version #{Bundler::VERSION}" : Bundler::VERSION)
+    end
+
+    private
+
+    def lockfile_bundled_with(version)
+      lockfile <<~L
+        GEM
+          remote: #{file_uri_for(gem_repo2)}/
+          specs:
+            rack (1.0.0)
+
+        PLATFORMS
+          #{lockfile_platforms}
+
+        DEPENDENCIES
+          rack
+
+        BUNDLED WITH
+           #{version}
+      L
+    end
+  end
+end
diff --git a/spec/bundler/support/filters.rb b/spec/bundler/support/filters.rb
index 3b91897a2e..96f2e2a274 100644
--- a/spec/bundler/support/filters.rb
+++ b/spec/bundler/support/filters.rb
@@ -28,6 +28,7 @@ RSpec.configure do |config|
 
   config.filter_run_excluding :git => RequirementChecker.against(git_version)
   config.filter_run_excluding :bundler => RequirementChecker.against(Bundler::VERSION.split(".")[0])
+  config.filter_run_excluding :rubygems => RequirementChecker.against(Gem::VERSION)
   config.filter_run_excluding :ruby_repo => !ENV["GEM_COMMAND"].nil?
   config.filter_run_excluding :no_color_tty => Gem.win_platform? || !ENV["GITHUB_ACTION"].nil?
   config.filter_run_excluding :permissions => Gem.win_platform?
diff --git a/spec/bundler/support/hax.rb b/spec/bundler/support/hax.rb
index 0ad5239128..4a49ffb49f 100644
--- a/spec/bundler/support/hax.rb
+++ b/spec/bundler/support/hax.rb
@@ -32,7 +32,7 @@ module Gem
   end
 
   if ENV["BUNDLER_SPEC_GEM_SOURCES"]
-    @sources = [ENV["BUNDLER_SPEC_GEM_SOURCES"]]
+    self.sources = [ENV["BUNDLER_SPEC_GEM_SOURCES"]]
   end
 
   # We only need this hack for rubygems versions without the BundlerVersionFinder
diff --git a/spec/bundler/support/helpers.rb b/spec/bundler/support/helpers.rb
index f84e68cee8..5238c8b980 100644
--- a/spec/bundler/support/helpers.rb
+++ b/spec/bundler/support/helpers.rb
@@ -166,7 +166,7 @@ module Spec
 
     def gem_command(command, options = {})
       env = options[:env] || {}
-      env["RUBYOPT"] = opt_add("-r#{spec_dir}/support/hax.rb", env["RUBYOPT"] || ENV["RUBYOPT"])
+      env["RUBYOPT"] = opt_add(opt_add("-r#{spec_dir}/support/hax.rb", env["RUBYOPT"]), ENV["RUBYOPT"])
       options[:env] = env
       sys_exec("#{Path.gem_bin} #{command}", options)
     end
@@ -181,7 +181,7 @@ module Spec
 
     def sys_exec(cmd, options = {})
       env = options[:env] || {}
-      env["RUBYOPT"] = opt_add("-r#{spec_dir}/support/switch_rubygems.rb", env["RUBYOPT"] || ENV["RUBYOPT"])
+      env["RUBYOPT"] = opt_add(opt_add("-r#{spec_dir}/support/switch_rubygems.rb", env["RUBYOPT"]), ENV["RUBYOPT"])
       dir = options[:dir] || bundled_app
       command_execution = CommandExecution.new(cmd.to_s, dir)
 
@@ -348,6 +348,7 @@ module Spec
       without_env_side_effects do
         ENV["GEM_HOME"] = path.to_s
         ENV["GEM_PATH"] = path.to_s
+        ENV["BUNDLER_ORIG_GEM_HOME"] = nil
         ENV["BUNDLER_ORIG_GEM_PATH"] = nil
         yield
       end
diff --git a/tool/bundler/rubocop_gems.rb.lock b/tool/bundler/rubocop_gems.rb.lock
index ca0fb5c613..4c33191c9e 100644
--- a/tool/bundler/rubocop_gems.rb.lock
+++ b/tool/bundler/rubocop_gems.rb.lock
@@ -60,4 +60,4 @@ DEPENDENCIES
   test-unit
 
 BUNDLED WITH
-   2.3.0.dev
+   2.3.0
diff --git a/tool/bundler/standard_gems.rb.lock b/tool/bundler/standard_gems.rb.lock
index af22080659..b29129ed57 100644
--- a/tool/bundler/standard_gems.rb.lock
+++ b/tool/bundler/standard_gems.rb.lock
@@ -66,4 +66,4 @@ DEPENDENCIES
   test-unit
 
 BUNDLED WITH
-   2.3.0.dev
+   2.3.0
diff --git a/tool/bundler/test_gems.rb.lock b/tool/bundler/test_gems.rb.lock
index 2f1dab91e2..d53195b0c9 100644
--- a/tool/bundler/test_gems.rb.lock
+++ b/tool/bundler/test_gems.rb.lock
@@ -41,4 +41,4 @@ DEPENDENCIES
   webrick (= 1.7.0)
 
 BUNDLED WITH
-   2.3.0.dev
+   2.3.0