10 files changed, 1065 insertions, 0 deletions

diff --git a/lib/bundler/plugin/api.rb b/lib/bundler/plugin/api.rb
new file mode 100644
index 0000000000..ee2bffe3ab
--- /dev/null
+++ b/lib/bundler/plugin/api.rb
@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+module Bundler
+  # This is the interfacing class represents the API that we intend to provide
+  # the plugins to use.
+  #
+  # For plugins to be independent of the Bundler internals they shall limit their
+  # interactions to methods of this class only. This will save them from breaking
+  # when some internal change.
+  #
+  # Currently we are delegating the methods defined in Bundler class to
+  # itself. So, this class acts as a buffer.
+  #
+  # If there is some change in the Bundler class that is incompatible to its
+  # previous behavior or if otherwise desired, we can reimplement(or implement)
+  # the method to preserve compatibility.
+  #
+  # To use this, either the class can inherit this class or use it directly.
+  # For example of both types of use, refer the file `spec/plugins/command.rb`
+  #
+  # To use it without inheriting, you will have to create an object of this
+  # to use the functions (except for declaration functions like command, source,
+  # and hooks).
+  module Plugin
+    class API
+      autoload :Source, File.expand_path("api/source", __dir__)
+
+      # The plugins should declare that they handle a command through this helper.
+      #
+      # @param [String] command being handled by them
+      # @param [Class] (optional) class that handles the command. If not
+      #                 provided, the `self` class will be used.
+      def self.command(command, cls = self)
+        Plugin.add_command command, cls
+      end
+
+      # The plugins should declare that they provide a installation source
+      # through this helper.
+      #
+      # @param [String] the source type they provide
+      # @param [Class] (optional) class that handles the source. If not
+      #                 provided, the `self` class will be used.
+      def self.source(source, cls = self)
+        cls.send :include, Bundler::Plugin::API::Source
+        Plugin.add_source source, cls
+      end
+
+      def self.hook(event, &block)
+        Plugin.add_hook(event, &block)
+      end
+
+      # The cache dir to be used by the plugins for storage
+      #
+      # @return [Pathname] path of the cache dir
+      def cache_dir
+        Plugin.cache.join("plugins")
+      end
+
+      # A tmp dir to be used by plugins
+      # Accepts names that get concatenated as suffix
+      #
+      # @return [Pathname] object for the new directory created
+      def tmp(*names)
+        Bundler.tmp(["plugin", *names].join("-"))
+      end
+
+      def method_missing(name, *args, &blk)
+        return Bundler.send(name, *args, &blk) if Bundler.respond_to?(name)
+
+        return SharedHelpers.send(name, *args, &blk) if SharedHelpers.respond_to?(name)
+
+        super
+      end
+
+      def respond_to_missing?(name, include_private = false)
+        SharedHelpers.respond_to?(name, include_private) ||
+          Bundler.respond_to?(name, include_private) || super
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/api/source.rb b/lib/bundler/plugin/api/source.rb
new file mode 100644
index 0000000000..798326673a
--- /dev/null
+++ b/lib/bundler/plugin/api/source.rb
@@ -0,0 +1,330 @@
+# frozen_string_literal: true
+
+module Bundler
+  module Plugin
+    class API
+      # This class provides the base to build source plugins
+      # All the method here are required to build a source plugin (except
+      # `uri_hash`, `gem_install_dir`; they are helpers).
+      #
+      # Defaults for methods, where ever possible are provided which is
+      # expected to work. But, all source plugins have to override
+      # `fetch_gemspec_files` and `install`. Defaults are also not provided for
+      # `remote!`, `cache!` and `unlock!`.
+      #
+      # The defaults shall work for most situations but nevertheless they can
+      # be (preferably should be) overridden as per the plugins' needs safely
+      # (as long as they behave as expected).
+      # On overriding `initialize` you should call super first.
+      #
+      # If required plugin should override `hash`, `==` and `eql?` methods to be
+      # able to match objects representing same sources, but may be created in
+      # different situation (like form gemfile and lockfile). The default ones
+      # checks only for class and uri, but elaborate source plugins may need
+      # more comparisons (e.g. git checking on branch or tag).
+      #
+      # @!attribute [r] uri
+      #   @return [String] the remote specified with `source` block in Gemfile
+      #
+      # @!attribute [r] options
+      #   @return [String] options passed during initialization (either from
+      #     lockfile or Gemfile)
+      #
+      # @!attribute [r] name
+      #   @return [String] name that can be used to uniquely identify a source
+      #
+      # @!attribute [rw] dependency_names
+      #   @return [Array<String>] Names of dependencies that the source should
+      #     try to resolve. It is not necessary to use this list internally. This
+      #     is present to be compatible with `Definition` and is used by
+      #     rubygems source.
+      module Source
+        attr_reader :uri, :options, :name, :checksum_store
+        attr_accessor :dependency_names
+
+        def initialize(opts)
+          @options = opts
+          @dependency_names = []
+          @uri = opts["uri"]
+          @type = opts["type"]
+          @name = opts["name"] || "#{@type} at #{@uri}"
+          @checksum_store = Checksum::Store.new
+        end
+
+        # This is used by the default `spec` method to constructs the
+        # Specification objects for the gems and versions that can be installed
+        # by this source plugin.
+        #
+        # Note: If the spec method is overridden, this function is not necessary
+        #
+        # @return [Array<String>] paths of the gemspec files for gems that can
+        #                         be installed
+        def fetch_gemspec_files
+          []
+        end
+
+        # Options to be saved in the lockfile so that the source plugin is able
+        # to check out same version of gem later.
+        #
+        # There options are passed when the source plugin is created from the
+        # lockfile.
+        #
+        # @return [Hash]
+        def options_to_lock
+          {}
+        end
+
+        # Download the gem specified by the spec at appropriate path.
+        #
+        # A source plugin can implement this method to split the download and the
+        # installation of a gem.
+        #
+        # @return [Boolean] Whether the download of the gem succeeded.
+        def download(spec, opts); end
+
+        # Install the gem specified by the spec at appropriate path.
+        # `install_path` provides a sufficient default, if the source can only
+        # satisfy one gem,  but is not binding.
+        #
+        # @return [String] post installation message (if any)
+        def install(spec, opts)
+          raise MalformattedPlugin, "Source plugins need to override the install method."
+        end
+
+        # It builds extensions, generates bins and installs them for the spec
+        # provided.
+        #
+        # It depends on `spec.loaded_from` to get full_gem_path. The source
+        # plugins should set that.
+        #
+        # It should be called in `install` after the plugin is done placing the
+        # gem at correct install location.
+        #
+        # It also runs Gem hooks `pre_install`, `post_build` and `post_install`
+        #
+        # Note: Do not override if you don't know what you are doing.
+        def post_install(spec, disable_exts = false)
+          opts = { env_shebang: false, disable_extensions: disable_exts }
+          installer = Bundler::Source::Path::Installer.new(spec, opts)
+          installer.post_install
+        end
+
+        # A default installation path to install a single gem. If the source
+        # servers multiple gems, it's not of much use and the source should one
+        # of its own.
+        def install_path
+          @install_path ||=
+            begin
+              base_name = File.basename(Gem::URI.parse(uri).normalize.path)
+
+              gem_install_dir.join("#{base_name}-#{uri_hash[0..11]}")
+            end
+        end
+
+        # Parses the gemspec files to find the specs for the gems that can be
+        # satisfied by the source.
+        #
+        # Few important points to keep in mind:
+        #   - If the gems are not installed then it shall return specs for all
+        #   the gems it can satisfy
+        #   - If gem is installed (that is to be detected by the plugin itself)
+        #   then it shall return at least the specs that are installed.
+        #   - The `loaded_from` for each of the specs shall be correct (it is
+        #   used to find the load path)
+        #
+        # @return [Bundler::Index] index containing the specs
+        def specs
+          files = fetch_gemspec_files
+
+          Bundler::Index.build do |index|
+            files.each do |file|
+              next unless spec = Bundler.load_gemspec(file)
+              spec.installed_by_version = Gem::VERSION
+
+              spec.source = self
+              Bundler.rubygems.validate(spec)
+
+              index << spec
+            end
+          end
+        end
+
+        # Set internal representation to fetch the gems/specs locally.
+        #
+        # When this is called, the source should try to fetch the specs and
+        # install from the local system.
+        def local!
+        end
+
+        # Set internal representation to fetch the gems/specs from remote.
+        #
+        # When this is called, the source should try to fetch the specs and
+        # install from remote path.
+        def remote!
+        end
+
+        # Set internal representation to fetch the gems/specs from app cache.
+        #
+        # When this is called, the source should try to fetch the specs and
+        # install from the path provided by `app_cache_path`.
+        def cached!
+        end
+
+        # This is called to update the spec and installation.
+        #
+        # If the source plugin is loaded from lockfile or otherwise, it shall
+        # refresh the cache/specs (e.g. git sources can make a fresh clone).
+        def unlock!
+        end
+
+        # Name of directory where plugin the is expected to cache the gems when
+        # #cache is called.
+        #
+        # Also this name is matched against the directories in cache for pruning
+        #
+        # This is used by `app_cache_path`
+        def app_cache_dirname
+          base_name = File.basename(Gem::URI.parse(uri).normalize.path)
+          "#{base_name}-#{uri_hash}"
+        end
+
+        # This method is called while caching to save copy of the gems that the
+        # source can resolve to path provided by `app_cache_app`so that they can
+        # be reinstalled from the cache without querying the remote (i.e. an
+        # alternative to remote)
+        #
+        # This is stored with the app and source plugins should try to provide
+        # specs and install only from this cache when `cached!` is called.
+        #
+        # This cache is different from the internal caching that can be done
+        # at sub paths of `cache_path` (from API). This can be though as caching
+        # by bundler.
+        def cache(spec, custom_path = nil)
+          new_cache_path = app_cache_path(custom_path)
+
+          FileUtils.rm_rf(new_cache_path)
+          FileUtils.cp_r(install_path, new_cache_path)
+          FileUtils.rm_rf(app_cache_path.join(".git"))
+          FileUtils.touch(app_cache_path.join(".bundlecache"))
+        end
+
+        # This shall check if two source object represent the same source.
+        #
+        # The comparison shall take place only on the attribute that can be
+        # inferred from the options passed from Gemfile and not on attributes
+        # that are used to pin down the gem to specific version (e.g. Git
+        # sources should compare on branch and tag but not on commit hash)
+        #
+        # The sources objects are constructed from Gemfile as well as from
+        # lockfile. To converge the sources, it is necessary that they match.
+        #
+        # The same applies for `eql?` and `hash`
+        def ==(other)
+          other.is_a?(self.class) && uri == other.uri
+        end
+
+        # When overriding `eql?` please preserve the behaviour as mentioned in
+        # docstring for `==` method.
+        alias_method :eql?, :==
+
+        # When overriding `hash` please preserve the behaviour as mentioned in
+        # docstring for `==` method, i.e. two methods equal by above comparison
+        # should have same hash.
+        def hash
+          [self.class, uri].hash
+        end
+
+        # A helper method, not necessary if not used internally.
+        def installed?
+          File.directory?(install_path)
+        end
+
+        # The full path where the plugin should cache the gem so that it can be
+        # installed latter.
+        #
+        # Note: Do not override if you don't know what you are doing.
+        def app_cache_path(custom_path = nil)
+          @app_cache_path ||= Bundler.app_cache(custom_path).join(app_cache_dirname)
+        end
+
+        # Used by definition.
+        #
+        # Note: Do not override if you don't know what you are doing.
+        def unmet_deps
+          specs.unmet_dependency_names
+        end
+
+        # Used by definition.
+        #
+        # Note: Do not override if you don't know what you are doing.
+        def spec_names
+          specs.spec_names
+        end
+
+        # Used by definition.
+        #
+        # Note: Do not override if you don't know what you are doing.
+        def add_dependency_names(names)
+          @dependencies |= Array(names)
+        end
+
+        # NOTE: Do not override if you don't know what you are doing.
+        def can_lock?(spec)
+          spec.source == self
+        end
+
+        # Generates the content to be entered into the lockfile.
+        # Saves type and remote and also calls to `options_to_lock`.
+        #
+        # Plugin should use `options_to_lock` to save information in lockfile
+        # and not override this.
+        #
+        # Note: Do not override if you don't know what you are doing.
+        def to_lock
+          out = String.new("#{LockfileParser::PLUGIN}\n")
+          out << "  remote: #{@uri}\n"
+          out << "  type: #{@type}\n"
+          options_to_lock.each do |opt, value|
+            out << "  #{opt}: #{value}\n"
+          end
+          out << "  specs:\n"
+        end
+
+        def to_s
+          "plugin source for #{@type} with uri #{@uri}"
+        end
+        alias_method :identifier, :to_s
+
+        # NOTE: Do not override if you don't know what you are doing.
+        def include?(other)
+          other == self
+        end
+
+        def uri_hash
+          SharedHelpers.digest(:SHA1).hexdigest(uri)
+        end
+
+        # NOTE: Do not override if you don't know what you are doing.
+        def gem_install_dir
+          Bundler.install_path
+        end
+
+        # It is used to obtain the full_gem_path.
+        #
+        # spec's loaded_from path is expanded against this to get full_gem_path
+        #
+        # Note: Do not override if you don't know what you are doing.
+        def root
+          Bundler.root
+        end
+
+        # @private
+        # This API on source might not be stable, and for now we expect plugins
+        # to download all specs in `#specs`, so we implement the method for
+        # compatibility purposes and leave it undocumented (and don't support)
+        # overriding it)
+        def double_check_for(*); end
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/dsl.rb b/lib/bundler/plugin/dsl.rb
new file mode 100644
index 0000000000..da751d1774
--- /dev/null
+++ b/lib/bundler/plugin/dsl.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module Bundler
+  module Plugin
+    # Dsl to parse the Gemfile looking for plugins to install
+    class DSL < Bundler::Dsl
+      class PluginGemfileError < PluginError; end
+      alias_method :_gem, :gem # To use for plugin installation as gem
+
+      # So that we don't have to override all there methods to dummy ones
+      # explicitly.
+      # They will be handled by method_missing
+      [:gemspec, :gem, :install_if, :platforms, :env].each {|m| undef_method m }
+
+      # This lists the plugins that was added automatically and not specified by
+      # the user.
+      #
+      # When we encounter :type attribute with a source block, we add a plugin
+      # by name bundler-source-<type> to list of plugins to be installed.
+      #
+      # These plugins are optional and are not installed when there is conflict
+      # with any other plugin.
+      attr_reader :inferred_plugins
+
+      def initialize
+        super
+        @sources = Plugin::SourceList.new
+        @inferred_plugins = [] # The source plugins inferred from :type
+      end
+
+      def plugin(name, *args)
+        _gem(name, *args)
+      end
+
+      def method_missing(name, *args)
+        raise PluginGemfileError, "Undefined local variable or method `#{name}' for Gemfile" unless Bundler::Dsl.method_defined? name
+      end
+
+      def source(source, *args, &blk)
+        options = args.last.is_a?(Hash) ? args.pop.dup : {}
+        options = normalize_hash(options)
+        return super unless options.key?("type")
+
+        plugin_name = "bundler-source-#{options["type"]}"
+
+        return if @dependencies.any? {|d| d.name == plugin_name }
+
+        plugin(plugin_name)
+        @inferred_plugins << plugin_name
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/events.rb b/lib/bundler/plugin/events.rb
new file mode 100644
index 0000000000..3fbf60307e
--- /dev/null
+++ b/lib/bundler/plugin/events.rb
@@ -0,0 +1,127 @@
+# frozen_string_literal: true
+
+module Bundler
+  module Plugin
+    module Events
+      def self.define(const, event)
+        const = const.to_sym.freeze
+        if const_defined?(const) && const_get(const) != event
+          raise ArgumentError, "Attempting to reassign #{const} to a different value"
+        end
+        const_set(const, event) unless const_defined?(const)
+        @events ||= {}
+        @events[event] = const
+      end
+      private_class_method :define
+
+      def self.reset
+        @events.each_value do |const|
+          remove_const(const)
+        end
+        @events = nil
+      end
+      private_class_method :reset
+
+      # Check if an event has been defined
+      # @param event [String] An event to check
+      # @return [Boolean] A boolean indicating if the event has been defined
+      def self.defined_event?(event)
+        @events ||= {}
+        @events.key?(event)
+      end
+
+      # @!parse
+      #   A hook called before the Gemfile is evaluated
+      #   Includes the Gemfile path and the Lockfile path
+      #   GEM_BEFORE_EVAL = "before-eval"
+      define :GEM_BEFORE_EVAL, "before-eval"
+
+      # @!parse
+      #   A hook called after the Gemfile is evaluated
+      #   Includes a Bundler::Definition
+      #   GEM_AFTER_EVAL = "after-eval"
+      define :GEM_AFTER_EVAL, "after-eval"
+
+      # @!parse
+      #   A hook called before any gems install
+      #   Includes an Array of Bundler::Dependency objects
+      #   GEM_BEFORE_INSTALL_ALL = "before-install-all"
+      define :GEM_BEFORE_INSTALL_ALL, "before-install-all"
+
+      # @!parse
+      #   A hook called before each individual gem is downloaded from a remote source.
+      #   Includes a spec-like object responding to the Gem::Specification API
+      #   (for example, a Bundler spec proxy such as Bundler::EndpointSpecification
+      #   or Bundler::RemoteSpecification). Does not fire when the gem is already
+      #   present at the initial download-cache check.
+      #   GEM_BEFORE_FETCH = "before-fetch"
+      define :GEM_BEFORE_FETCH, "before-fetch"
+
+      # @!parse
+      #   A hook called after each individual gem is downloaded from a remote source.
+      #   Includes a spec-like object responding to the Gem::Specification API
+      #   (for example, a Bundler spec proxy such as Bundler::EndpointSpecification
+      #   or Bundler::RemoteSpecification). Does not fire when the gem is already
+      #   present at the initial download-cache check.
+      #   GEM_AFTER_FETCH = "after-fetch"
+      define :GEM_AFTER_FETCH, "after-fetch"
+
+      # @!parse
+      #   A hook called before a git source is fetched or checked out.
+      #   Includes a Bundler::Source::Git reference.
+      #   GIT_BEFORE_FETCH = "before-git-fetch"
+      define :GIT_BEFORE_FETCH, "before-git-fetch"
+
+      # @!parse
+      #   A hook called after a git source is fetched or checked out.
+      #   Includes a Bundler::Source::Git reference.
+      #   GIT_AFTER_FETCH = "after-git-fetch"
+      define :GIT_AFTER_FETCH, "after-git-fetch"
+
+      # @!parse
+      #   A hook called before each individual gem is installed
+      #   Includes a Bundler::ParallelInstaller::SpecInstallation.
+      #   No state, error, post_install_message will be present as nothing has installed yet
+      #   GEM_BEFORE_INSTALL = "before-install"
+      define :GEM_BEFORE_INSTALL, "before-install"
+
+      # @!parse
+      #   A hook called after each individual gem is installed
+      #   Includes a Bundler::ParallelInstaller::SpecInstallation.
+      #     - If state is failed, an error will be present.
+      #     - If state is success, a post_install_message may be present.
+      #   GEM_AFTER_INSTALL = "after-install"
+      define :GEM_AFTER_INSTALL,  "after-install"
+
+      # @!parse
+      #   A hook called after any gems install
+      #   Includes an Array of Bundler::Dependency objects
+      #   GEM_AFTER_INSTALL_ALL = "after-install-all"
+      define :GEM_AFTER_INSTALL_ALL,  "after-install-all"
+
+      # @!parse
+      #   A hook called before any gems require
+      #   Includes an Array of Bundler::Dependency objects.
+      #   GEM_BEFORE_REQUIRE_ALL = "before-require-all"
+      define :GEM_BEFORE_REQUIRE_ALL, "before-require-all"
+
+      # @!parse
+      #   A hook called before each individual gem is required
+      #   Includes a Bundler::Dependency.
+      #   GEM_BEFORE_REQUIRE = "before-require"
+      define :GEM_BEFORE_REQUIRE, "before-require"
+
+      # @!parse
+      #   A hook called after each individual gem is required
+      #   Includes a Bundler::Dependency.
+      #   GEM_AFTER_REQUIRE = "after-require"
+      define :GEM_AFTER_REQUIRE,  "after-require"
+
+      # @!parse
+      #   A hook called after all gems required
+      #   Includes an Array of Bundler::Dependency objects.
+      #   GEM_AFTER_REQUIRE_ALL = "after-require-all"
+      define :GEM_AFTER_REQUIRE_ALL, "after-require-all"
+    end
+  end
+end
diff --git a/lib/bundler/plugin/index.rb b/lib/bundler/plugin/index.rb
new file mode 100644
index 0000000000..1dfb061304
--- /dev/null
+++ b/lib/bundler/plugin/index.rb
@@ -0,0 +1,241 @@
+# frozen_string_literal: true
+
+module Bundler
+  # Manages which plugins are installed and their sources. This also is supposed to map
+  # which plugin does what (currently the features are not implemented so this class is
+  # now a stub class).
+  module Plugin
+    class Index
+      class CommandConflict < PluginError
+        def initialize(plugin, commands)
+          msg = "Command(s) `#{commands.join("`, `")}` declared by #{plugin} are already registered."
+          super msg
+        end
+      end
+
+      class SourceConflict < PluginError
+        def initialize(plugin, sources)
+          msg = "Source(s) `#{sources.join("`, `")}` declared by #{plugin} are already registered."
+          super msg
+        end
+      end
+
+      attr_reader :commands
+
+      def initialize
+        @plugin_paths = {}
+        @commands = {}
+        @sources = {}
+        @hooks = {}
+        @load_paths = {}
+
+        begin
+          load_index(global_index_file, true)
+        rescue PermissionError
+          # no need to fail when on a read-only FS, for example
+          nil
+        rescue ArgumentError => e
+          # ruby 3.4 checks writability in Dir.tmpdir
+          raise unless e.message&.include?("could not find a temporary directory")
+          nil
+        end
+        load_index(local_index_file) if SharedHelpers.in_bundle?
+      end
+
+      # This function is to be called when a new plugin is installed. This
+      # function shall add the functions of the plugin to existing maps and also
+      # the name to source location.
+      #
+      # @param [String] name of the plugin to be registered
+      # @param [String] path where the plugin is installed
+      # @param [Array<String>] load_paths for the plugin
+      # @param [Array<String>] commands that are handled by the plugin
+      # @param [Array<String>] sources that are handled by the plugin
+      def register_plugin(name, path, load_paths, commands, sources, hooks)
+        old_commands = @commands.dup
+
+        common = commands & @commands.keys
+        raise CommandConflict.new(name, common) unless common.empty?
+        commands.each {|c| @commands[c] = name }
+
+        common = sources & @sources.keys
+        raise SourceConflict.new(name, common) unless common.empty?
+        sources.each {|k| @sources[k] = name }
+
+        hooks.each do |event|
+          event_hooks = (@hooks[event] ||= []) << name
+          event_hooks.uniq!
+        end
+
+        @plugin_paths[name] = path
+        @load_paths[name] = load_paths
+        save_index
+      rescue StandardError
+        @commands = old_commands
+        raise
+      end
+
+      def unregister_plugin(name)
+        @commands.delete_if {|_, v| v == name }
+        @sources.delete_if {|_, v| v == name }
+        @hooks.each do |hook, names|
+          names.delete(name)
+          @hooks.delete(hook) if names.empty?
+        end
+        @plugin_paths.delete(name)
+        @load_paths.delete(name)
+        save_index
+      end
+
+      # Path of default index file
+      def index_file
+        Plugin.root.join("index")
+      end
+
+      # Path where the global index file is stored
+      def global_index_file
+        Plugin.global_root.join("index")
+      end
+
+      # Path where the local index file is stored
+      def local_index_file
+        Plugin.local_root.join("index")
+      end
+
+      def plugin_path(name)
+        Pathname.new @plugin_paths[name]
+      end
+
+      def load_paths(name)
+        @load_paths[name]
+      end
+
+      # Fetch the name of plugin handling the command
+      def command_plugin(command)
+        @commands[command]
+      end
+
+      def installed?(name)
+        @plugin_paths[name]
+      end
+
+      def up_to_date?(spec)
+        path = installed?(spec.name)
+
+        path == spec.full_gem_path
+      end
+
+      def installed_plugins
+        @plugin_paths.keys
+      end
+
+      def plugin_commands(plugin)
+        @commands.find_all {|_, n| n == plugin }.map(&:first)
+      end
+
+      def source?(source)
+        @sources.key? source
+      end
+
+      def source_plugin(name)
+        @sources[name]
+      end
+
+      # Returns the list of plugin names handling the passed event
+      def hook_plugins(event)
+        @hooks[event] || []
+      end
+
+      # This plugin is installed inside the .bundle/plugin directory,
+      # and thus is managed solely by Bundler
+      def installed_in_plugin_root?(name)
+        return false unless (path = installed?(name))
+
+        path.start_with?("#{Plugin.root}/")
+      end
+
+      private
+
+      # Reads the index file from the directory and initializes the instance
+      # variables.
+      #
+      # It skips the sources if the second param is true
+      # @param [Pathname] index file path
+      # @param [Boolean] is the index file global index
+      def load_index(index_file, global = false)
+        base = base_for_index(global)
+
+        SharedHelpers.filesystem_access(index_file, :read) do |index_f|
+          valid_file = index_f&.exist? && !index_f.size.zero?
+          break unless valid_file
+
+          data = index_f.read
+
+          require_relative "../yaml_serializer"
+          index = YAMLSerializer.load(data)
+
+          @commands.merge!(index["commands"])
+          @hooks.merge!(index["hooks"])
+          @load_paths.merge!(transform_index_paths(index["load_paths"]) {|p| absolutize_path(p, base) })
+          @plugin_paths.merge!(transform_index_paths(index["plugin_paths"]) {|p| absolutize_path(p, base) })
+          @sources.merge!(index["sources"]) unless global
+        end
+      end
+
+      # Should be called when any of the instance variables change. Stores the
+      # instance variables in YAML format. (The instance variables are supposed
+      # to be only String key value pairs)
+      def save_index
+        base = base_for_index(false)
+
+        index = {
+          "commands" => @commands,
+          "hooks" => @hooks,
+          "load_paths" => transform_index_paths(@load_paths) {|p| relativize_path(p, base) },
+          "plugin_paths" => transform_index_paths(@plugin_paths) {|p| relativize_path(p, base) },
+          "sources" => @sources,
+        }
+
+        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) }
+        end
+      end
+
+      def base_for_index(global)
+        global ? Plugin.global_root : Plugin.root
+      end
+
+      def transform_index_paths(paths)
+        return {} unless paths
+
+        paths.transform_values do |value|
+          if value.is_a?(Array)
+            value.map {|path| yield path }
+          else
+            yield value
+          end
+        end
+      end
+
+      def relativize_path(path, base)
+        pathname = Pathname.new(path)
+        return path unless pathname.absolute?
+
+        base_path = Pathname.new(base)
+        if pathname == base_path || pathname.to_s.start_with?(base_path.to_s + File::SEPARATOR)
+          pathname.relative_path_from(base_path).to_s
+        else
+          path
+        end
+      end
+
+      def absolutize_path(path, base)
+        pathname = Pathname.new(path)
+        pathname = Pathname.new(base).join(pathname) unless pathname.absolute?
+        pathname.to_s
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/installer.rb b/lib/bundler/plugin/installer.rb
new file mode 100644
index 0000000000..9be8b36843
--- /dev/null
+++ b/lib/bundler/plugin/installer.rb
@@ -0,0 +1,123 @@
+# frozen_string_literal: true
+
+module Bundler
+  # Handles the installation of plugin in appropriate directories.
+  #
+  # This class is supposed to be wrapper over the existing gem installation infra
+  # but currently it itself handles everything as the Source's subclasses (e.g. Source::RubyGems)
+  # are heavily dependent on the Gemfile.
+  module Plugin
+    class Installer
+      autoload :Rubygems, File.expand_path("installer/rubygems", __dir__)
+      autoload :Git,      File.expand_path("installer/git", __dir__)
+      autoload :Path, File.expand_path("installer/path", __dir__)
+
+      def install(names, options)
+        check_sources_consistency!(options)
+
+        version = options[:version] || [">= 0"]
+
+        if options[:git]
+          install_git(names, version, options)
+        elsif options[:path]
+          install_path(names, version, options[:path])
+        else
+          sources = options[:source] || Gem.sources
+          install_rubygems(names, version, sources)
+        end
+      end
+
+      # Installs the plugin from Definition object created by limited parsing of
+      # Gemfile searching for plugins to be installed
+      #
+      # @param [Definition] definition object
+      # @return [Hash] map of names to their specs they are installed with
+      def install_definition(definition)
+        def definition.lock(*); end
+        definition.remotely!
+        specs = definition.specs
+
+        install_from_specs specs
+      end
+
+      private
+
+      def check_sources_consistency!(options)
+        if (options.keys & [:source, :git, :path]).length > 1
+          raise InvalidOption, "Only one of --source, --git, or --path may be specified"
+        end
+
+        if (options.key?(:branch) || options.key?(:ref)) && !options.key?(:git)
+          raise InvalidOption, "--#{options.key?(:branch) ? "branch" : "ref"} can only be used with git sources"
+        end
+
+        if options.key?(:branch) && options.key?(:ref)
+          raise InvalidOption, "--branch and --ref can't be both specified"
+        end
+      end
+
+      def install_git(names, version, options)
+        source_list = SourceList.new
+        source = source_list.add_git_source({ "uri" => options[:git],
+                                              "branch" => options[:branch],
+                                              "ref" => options[:ref] })
+
+        install_all_sources(names, version, source_list, source)
+      end
+
+      def install_path(names, version, path)
+        source_list = SourceList.new
+        source = source_list.add_path_source({ "path" => path, "root_path" => SharedHelpers.pwd })
+
+        install_all_sources(names, version, source_list, source)
+      end
+
+      # Installs the plugin from rubygems source and returns the path where the
+      # plugin was installed
+      #
+      # @param [String] name of the plugin gem to search in the source
+      # @param [Array] version of the gem to install
+      # @param [String, Array<String>] source(s) to resolve the gem
+      #
+      # @return [Hash] map of names to the specs of plugins installed
+      def install_rubygems(names, version, sources)
+        source_list = SourceList.new
+
+        Array(sources).each {|remote| source_list.add_global_rubygems_remote(remote) }
+
+        install_all_sources(names, version, source_list)
+      end
+
+      def install_all_sources(names, version, source_list, source = nil)
+        deps = names.map {|name| Dependency.new(name, version, { "source" => source }) }
+
+        Bundler.configure_gem_home_and_path(Plugin.root)
+
+        Bundler.settings.temporary(deployment: false, frozen: false) do
+          definition = Definition.new(nil, deps, source_list, true)
+
+          install_definition(definition)
+        end
+      end
+
+      # Installs the plugins and deps from the provided specs and returns map of
+      # gems to their paths
+      #
+      # @param specs to install
+      #
+      # @return [Hash] map of names to the specs
+      def install_from_specs(specs)
+        paths = {}
+
+        specs.each do |spec|
+          spec.source.download(spec)
+          spec.source.install(spec)
+
+          paths[spec.name] = spec
+        end
+
+        paths
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/installer/git.rb b/lib/bundler/plugin/installer/git.rb
new file mode 100644
index 0000000000..deec5e99b3
--- /dev/null
+++ b/lib/bundler/plugin/installer/git.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module Bundler
+  module Plugin
+    class Installer
+      class Git < Bundler::Source::Git
+        def cache_path
+          @cache_path ||= begin
+            git_scope = "#{base_name}-#{uri_hash}"
+
+            Plugin.cache.join("bundler", "git", git_scope)
+          end
+        end
+
+        def install_path
+          @install_path ||= begin
+            git_scope = "#{base_name}-#{shortref_for_path(revision)}"
+
+            Plugin.root.join("bundler", "gems", git_scope)
+          end
+        end
+
+        def root
+          Plugin.root
+        end
+
+        def generate_bin(spec, disable_extensions = false)
+          # Need to find a way without code duplication
+          # For now, we can ignore this
+        end
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/installer/path.rb b/lib/bundler/plugin/installer/path.rb
new file mode 100644
index 0000000000..58c4924eb0
--- /dev/null
+++ b/lib/bundler/plugin/installer/path.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module Bundler
+  module Plugin
+    class Installer
+      class Path < Bundler::Source::Path
+        def root
+          SharedHelpers.in_bundle? ? Bundler.root : Plugin.root
+        end
+
+        def eql?(other)
+          return unless other.class == self.class
+          expanded_original_path == other.expanded_original_path &&
+            version == other.version
+        end
+
+        alias_method :==, :eql?
+
+        def generate_bin(spec, disable_extensions = false)
+          # Need to find a way without code duplication
+          # For now, we can ignore this
+        end
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/installer/rubygems.rb b/lib/bundler/plugin/installer/rubygems.rb
new file mode 100644
index 0000000000..cb5db9c30e
--- /dev/null
+++ b/lib/bundler/plugin/installer/rubygems.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module Bundler
+  module Plugin
+    class Installer
+      class Rubygems < Bundler::Source::Rubygems
+        private
+
+        def rubygems_dir
+          Plugin.root
+        end
+
+        def cache_path
+          Plugin.cache
+        end
+      end
+    end
+  end
+end
diff --git a/lib/bundler/plugin/source_list.rb b/lib/bundler/plugin/source_list.rb
new file mode 100644
index 0000000000..d929ade29e
--- /dev/null
+++ b/lib/bundler/plugin/source_list.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Bundler
+  # SourceList object to be used while parsing the Gemfile, setting the
+  # approptiate options to be used with Source classes for plugin installation
+  module Plugin
+    class SourceList < Bundler::SourceList
+      def add_git_source(options = {})
+        add_source_to_list Plugin::Installer::Git.new(options), git_sources
+      end
+
+      def add_path_source(options = {})
+        add_source_to_list Plugin::Installer::Path.new(options), path_sources
+      end
+
+      def add_rubygems_source(options = {})
+        add_source_to_list Plugin::Installer::Rubygems.new(options), @rubygems_sources
+      end
+
+      def all_sources
+        path_sources + git_sources + rubygems_sources + [metadata_source]
+      end
+
+      private
+
+      def source_class
+        Plugin::Installer::Rubygems
+      end
+    end
+  end
+end