Accept multiple config files from command line

Parse config as if it can contain multiple references to config files.
This allows you to pass in multiple config files from the command line

Helps with issues #514 and #703

lib/jekyll.rb

@@ -136,13 +136,19 @@ module Jekyll
     source = override['source'] || Jekyll::DEFAULTS['source']
 
     # Get configuration from <source>/_config.yml or <source>/<config_file>
-    config_file = override.delete('config')
-    config_file = File.join(source, "_config.yml") if config_file.to_s.empty?
+    config_files = override.delete('config')
+    config_files = File.join(source, "_config.yml") if config_files.to_s.empty?
+    # If config is a list of space separate config files
+    config_files = config_files.split(' ')
 
     begin
-      config = YAML.safe_load_file(config_file)
-      raise "Configuration file: (INVALID) #{config_file}" if !config.is_a?(Hash)
-      $stdout.puts "Configuration file: #{config_file}"
+      config = {}
+      config_files.each do |config_file|
+        next_config = YAML.safe_load_file(config_file)
+        raise "Configuration file: (INVALID) #{config_file}" if !next_config.is_a?(Hash)
+        $stdout.puts "Configuration file: #{config_file}"
+        config = config.deep_merge(next_config)
+      end
     rescue SystemCallError
       # Errno:ENOENT = file not found
       $stderr.puts "Configuration file: none"

test/test_configuration.rb

@@ -46,10 +46,20 @@ class TestConfiguration < Test::Unit::TestCase
       assert_equal Jekyll::DEFAULTS.deep_merge({ "baseurl" => "http://wahoo.dev" }), Jekyll.configuration({ "config" => @paths[:other] })
     end
 
-    should "load default config if path passed is empty" do
+    should "load multiple config files" do
       mock(YAML).safe_load_file(@paths[:default]) { Hash.new }
+      mock(YAML).safe_load_file(@paths[:other]) { Hash.new }
       mock($stdout).puts("Configuration file: #{@paths[:default]}")
-      assert_equal Jekyll::DEFAULTS, Jekyll.configuration({ "config" => @paths[:empty] })
+      mock($stdout).puts("Configuration file: #{@paths[:other]}")
+      assert_equal Jekyll::DEFAULTS, Jekyll.configuration({ "config" => "#{@paths[:default]} #{@paths[:other]}" })
+    end
+
+    should "load multiple config files and last config should win" do
+      mock(YAML).safe_load_file(@paths[:default]) { {"baseurl" => "http://example.dev"} }
+      mock(YAML).safe_load_file(@paths[:other]) { {"baseurl" => "http://wahoo.dev"} }
+      mock($stdout).puts("Configuration file: #{@paths[:default]}")
+      mock($stdout).puts("Configuration file: #{@paths[:other]}")
+      assert_equal Jekyll::DEFAULTS.deep_merge({ "baseurl" => "http://wahoo.dev" }), Jekyll.configuration({ "config" => "#{@paths[:default]} #{@paths[:other]}" })
     end
   end
 end