1 files changed, 186 insertions, 0 deletions
diff --git a/lib/bundler/self_manager.rb b/lib/bundler/self_manager.rb
new file mode 100644
index 0000000000..bfd000b1a0
--- /dev/null
+++ b/lib/bundler/self_manager.rb
@@ -0,0 +1,186 @@
+# 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(restart_version)
+    end
+
+    def install_locked_bundler_and_restart_with_it_if_needed
+      return unless needs_switching?
+
+      if restart_version == lockfile_version
+        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."
+      else
+        Bundler.ui.info \
+          "Bundler #{current_version} is running, but your configuration was #{restart_version}. " \
+          "Installing Bundler #{restart_version} and restarting using that version."
+      end
+
+      install_and_restart_with(restart_version)
+    end
+
+    def update_bundler_and_restart_with_it_if_needed(target)
+      return unless autoswitching_applies?
+
+      spec = resolve_update_version_from(target)
+      return unless spec
+
+      version = spec.version
+
+      Bundler.ui.info "Updating bundler to #{version}."
+
+      install(spec)
+
+      restart_with(version)
+    end
+
+    private
+
+    def install_and_restart_with(version)
+      requirement = Gem::Requirement.new(version)
+      spec = find_latest_matching_spec(requirement)
+
+      if spec.nil?
+        Bundler.ui.warn "Your lockfile is locked to a version of bundler (#{lockfile_version}) that doesn't exist at https://rubygems.org/. Going on using #{current_version}"
+        return
+      end
+
+      install(spec)
+    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(version)
+    end
+
+    def install(spec)
+      spec.source.install(spec)
+    end
+
+    def restart_with(version)
+      configured_gem_home = ENV["GEM_HOME"]
+      configured_gem_path = ENV["GEM_PATH"]
+
+      cmd = [$PROGRAM_NAME, *ARGV]
+      cmd.unshift(Gem.ruby) unless File.executable?($PROGRAM_NAME)
+
+      Bundler.with_original_env do
+        Kernel.exec(
+          { "GEM_HOME" => configured_gem_home, "GEM_PATH" => configured_gem_path, "BUNDLER_VERSION" => version.to_s },
+          *cmd
+        )
+      end
+    end
+
+    def needs_switching?
+      autoswitching_applies? &&
+        released?(lockfile_version) &&
+        !running?(lockfile_version) &&
+        !updating? &&
+        Bundler.settings[:version] != "system"
+    end
+
+    def autoswitching_applies?
+      ENV["BUNDLER_VERSION"].nil? &&
+        Bundler.rubygems.supports_bundler_trampolining? &&
+        SharedHelpers.in_bundle? &&
+        lockfile_version
+    end
+
+    def resolve_update_version_from(target)
+      requirement = Gem::Requirement.new(target)
+      update_candidate = find_latest_matching_spec(requirement)
+
+      if update_candidate.nil?
+        raise InvalidOption, "The `bundle update --bundler` target version (#{target}) does not exist"
+      end
+
+      resolved_version = update_candidate.version
+      needs_update = requirement.specific? ? !running?(resolved_version) : running_older_than?(resolved_version)
+
+      return unless needs_update
+
+      update_candidate
+    end
+
+    def local_specs
+      @local_specs ||= Bundler::Source::Rubygems.new("allow_local" => true, "allow_cached" => true).specs.select {|spec| spec.name == "bundler" }
+    end
+
+    def remote_specs
+      @remote_specs ||= begin
+        source = Bundler::Source::Rubygems.new("remotes" => "https://rubygems.org")
+        source.remote!
+        source.add_dependency_names("bundler")
+        source.specs.select(&:matches_current_metadata?)
+      end
+    end
+
+    def find_latest_matching_spec(requirement)
+      local_result = find_latest_matching_spec_from_collection(local_specs, requirement)
+      return local_result if local_result && requirement.specific?
+
+      remote_result = find_latest_matching_spec_from_collection(remote_specs, requirement)
+      return remote_result if local_result.nil?
+
+      [local_result, remote_result].max
+    end
+
+    def find_latest_matching_spec_from_collection(specs, requirement)
+      specs.sort.reverse_each.find {|spec| requirement.satisfied_by?(spec.version) }
+    end
+
+    def running?(version)
+      version == current_version
+    end
+
+    def running_older_than?(version)
+      current_version < version
+    end
+
+    def released?(version)
+      !version.to_s.end_with?(".dev")
+    end
+
+    def updating?
+      "update".start_with?(ARGV.first || " ") && ARGV[1..-1].any? {|a| a.start_with?("--bundler") }
+    end
+
+    def installed?
+      Bundler.configure
+
+      Bundler.rubygems.find_bundler(restart_version.to_s)
+    end
+
+    def current_version
+      @current_version ||= Gem::Version.new(Bundler::VERSION)
+    end
+
+    def lockfile_version
+      return @lockfile_version if defined?(@lockfile_version)
+
+      parsed_version = Bundler::LockfileParser.bundled_with
+      @lockfile_version = parsed_version ? Gem::Version.new(parsed_version) : nil
+    rescue ArgumentError
+      @lockfile_version = nil
+    end
+
+    def restart_version
+      return @restart_version if defined?(@restart_version)
+      # BUNDLE_VERSION=x.y.z
+      @restart_version = Gem::Version.new(Bundler.settings[:version])
+    rescue ArgumentError
+      # BUNDLE_VERSION=lockfile
+      @restart_version = lockfile_version
+    end
+  end
+end