Allow loading config file from plugin directory

`plugin_directories` property can be used in `.scss-linter.yml` to
load additional linters from a directory. However it does not allow
loading custom `.scss-linter.yml` for such directory.

This commit allows loading a custom `.scss-linter.yml` from any
directory specified in `plugin_directories` and merge it with
your existing configuration.

lib/scss_lint/plugins/linter_dir.rb

@@ -6,11 +6,11 @@ class LinterDir
 
       def initialize(dir)
         @dir = dir
-        @config = SCSSLint::Config.new({}) # Will always be empty
       end
 
       def load
         ruby_files.each { |file| require file }
+        @config = plugin_config
         self
       end
 
@@ -19,6 +19,29 @@ def load
       def ruby_files
         Dir.glob(File.expand_path(File.join(@dir, '**', '*.rb')))
       end
+
+      # Returns the {SCSSLint::Config} for this directory.
+      #
+      # This is intended to be merged with the configuration that loaded this
+      # plugin.
+      #
+      # @return [SCSSLint::Config]
+      def plugin_config
+        file = plugin_config_file
+
+        if File.exist?(file)
+          Config.load(file, merge_with_default: false)
+        else
+          Config.new({})
+        end
+      end
+
+      # Path of the configuration file to attempt to load for this directory.
+      #
+      # @return [String]
+      def plugin_config_file
+        File.join(@dir, Config::FILE_NAME)
+      end
     end
   end
 end

spec/scss_lint/plugins/linter_dir_spec.rb

@@ -4,18 +4,42 @@
   let(:plugin_directory) { File.expand_path('../../fixtures/plugins', __FILE__) }
   let(:subject) { described_class.new(plugin_directory) }
 
-  describe '#config' do
-    it 'returns empty configuration' do
-      subject.config.should == SCSSLint::Config.new({})
+  describe '#load' do
+    let(:config_file) { File.join(plugin_directory, '.scss-lint.yml') }
+    let(:config_file_exists) { false }
+
+    before do
+      File.stub(:exist?).with(config_file).and_return(config_file_exists)
     end
-  end
 
-  describe '#load' do
     it 'requires each file in the plugin directory' do
       subject.should_receive(:require)
              .with(File.join(plugin_directory, 'linter_plugin.rb')).once
 
       subject.load
     end
+
+    context 'when the dir does not include a configuration file' do
+      it 'loads an empty configuration' do
+        subject.load
+        subject.config.should == SCSSLint::Config.new({})
+      end
+    end
+
+    context 'when a config file exists in the dir' do
+      let(:config_file_exists) { true }
+      let(:fake_config) { SCSSLint::Config.new('linters' => { 'FakeLinter' => {} }) }
+
+      before do
+        SCSSLint::Config.should_receive(:load)
+                        .with(config_file, merge_with_default: false)
+                        .and_return(fake_config)
+      end
+
+      it 'loads the configuration' do
+        subject.load
+        subject.config.should == fake_config
+      end
+    end
   end
 end