Adds initial Plugin with native git plugin example

Author: codenamev

lib/git_commander.rb

@@ -2,6 +2,7 @@
 
 require "git_commander/command"
 require "git_commander/logger"
+require "git_commander/plugin"
 require "git_commander/registry"
 require "git_commander/system"
 require "git_commander/version"

lib/git_commander/plugin.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require_relative "plugin/executor"
+
+module GitCommander
+  #
+  # @abstract Allows for proxying methods to a plugin from within the context of
+  # a Command's block.
+  #
+  # A Plugin provides additional external instances to a Command's @block
+  # context.  Plugins can define their own inline gems, and can define
+  # additional Commands.
+  #
+  # @example Loadable Command file with native `git` plugin
+  #   # This is a unique example of using `plugin` without any options.  It
+  #   # uses the `git` plugin provided natively with this gem. Most times you will
+  #   # use a path: "path/to/my/plugin", or url: "https://example.com/myplugin"
+  #   plugin :git
+  #   command :local_branches do |cmd|
+  #     git.branches.local.map(&:name)
+  #   end
+  #
+  class Plugin
+    attr_accessor :executor, :name, :registry
+
+    # Creates a Plugin object. +name+ is the name of the plugin.
+    #
+    # Options include:
+    #
+    # +source_instance+ - an instance of an object to use in the Command's block context
+    # +registry+ - a Registry instance for where this Plugin will be stored for lookup
+    def initialize(name, source_instance: nil, registry: nil)
+      @name = name
+      @executor = Executor.new(source_instance) if source_instance
+      @registry = registry || GitCommander::Registry.new
+    end
+  end
+end

lib/git_commander/plugin/executor.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+require "delegate"
+
+module GitCommander
+  class Plugin
+    class Executor < SimpleDelegator
+    end
+  end
+end

lib/git_commander/plugins/git.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+gemfile do
+  source "https://rubygems.org"
+  gem "git"
+  gem "rspec" # This is a stop-gap to allow testing of these in the context of the gem
+end
+
+Git.open Dir.pwd, log: GitCommander.logger

spec/lib/git_commander/plugin_spec.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+describe GitCommander::Plugin do
+  it "initializes an Executor with the provided block" do
+    source_instance = Object.new
+    expect(described_class::Executor).to receive(:new).with(source_instance)
+    described_class.new :git, source_instance: source_instance
+  end
+end