Separate jekyll-docs out into a separate gem & bless it

bin/jekyll

@@ -6,12 +6,9 @@ $:.unshift File.join(File.dirname(__FILE__), *%w{ .. lib })
 require 'jekyll'
 require 'mercenary'
 
-%w[jekyll-import].each do |blessed_gem|
-  begin
-    require blessed_gem
-  rescue LoadError
-  end
-end
+Jekyll::External.require_if_present(
+  Jekyll::External.blessed_gems
+)
 
 Jekyll::PluginManager.require_from_bundler
 

lib/jekyll/commands/docs.rb

@@ -1,30 +0,0 @@
-module Jekyll
-  module Commands
-    class Docs < Command
-
-      class << self
-
-        def init_with_program(prog)
-          prog.command(:docs) do |c|
-            c.syntax 'docs'
-            c.description "Launch local server with docs for Jekyll v#{Jekyll::VERSION}"
-
-            c.option 'port', '-P', '--port [PORT]', 'Port to listen on'
-            c.option 'host', '-H', '--host [HOST]', 'Host to bind to'
-
-            c.action do |args, options|
-              options.merge!({
-                'source'      => File.expand_path("../../../site", File.dirname(__FILE__)),
-                'destination' => File.expand_path("../../../site/_site", File.dirname(__FILE__))
-              })
-              Jekyll::Commands::Build.process(options)
-              Jekyll::Commands::Serve.process(options)
-            end
-          end
-        end
-
-      end
-
-    end
-  end
-end

lib/jekyll/external.rb

@@ -0,0 +1,59 @@
+module Jekyll
+  module External
+    class << self
+
+      #
+      # Gems that, if installed, should be loaded.
+      # Usually contain subcommands.
+      #
+      def blessed_gems
+        %w{
+          jekyll-docs
+          jekyll-import
+        }
+      end
+
+      #
+      # Require a gem or file if it's present, otherwise silently fail.
+      #
+      # names - a string gem name or array of gem names
+      #
+      def require_if_present(names)
+        Array(names).each do |name|
+          begin
+            require name
+          rescue LoadError
+            Jekyll.logger.debug "Couldn't load #{name}. Skipping."
+            false
+          end
+        end
+      end
+
+      #
+      # Require a gem or gems. If it's not present, show a very nice error
+      # message that explains everything and is much more helpful than the
+      # normal LoadError.
+      #
+      # names - a string gem name or array of gem names
+      #
+      def require_with_graceful_fail(names)
+        Array(names).each do |name|
+          begin
+            require name
+          rescue LoadError => e
+            Jekyll.logger.error "Dependency Error:", <<-MSG
+Yikes! It looks like you don't have #{name} or one of its dependencies installed.
+In order to use Jekyll as currently configured, you'll need to install this gem.
+
+The full error message from Ruby is: '#{e.message}'
+
+If you run into trouble, you can find helpful resources at http://jekyllrb.com/help/!
+            MSG
+            raise Jekyll::Errors::MissingDependencyException.new(name)
+          end
+        end
+      end
+
+    end
+  end
+end

site/_docs/usage.md

@@ -81,4 +81,7 @@ $ jekyll build --source _source --destination _deploy
 {% endhighlight %}
 
 For more about the possible configuration options, see the
-[configuration](../configuration/) page.
+[configuration](../configuration/) page.
+
+If you're interested in browsing these docs on-the-go, install the
+`jekyll-docs` gem and run `jekyll docs` in your terminal.