3 files changed, 134 insertions, 0 deletions
diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 3b71f2c2a3..e9abfac7a0 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,21 @@
+*   Add `Rails::Application.config_for` to load a configuration for the current
+    environment.
+
+        # config/exception_notification.yml:
+        production:
+          url: http://127.0.0.1:8080
+          namespace: my_app_production
+        development:
+          url: http://localhost:3001
+          namespace: my_app_development
+
+        # config/production.rb
+        MyApp::Application.configure do
+          config.middleware.use ExceptionNotifier, config_for(:exception_notification)
+        end
+
+    *Rafael Mendonça França*, *DHH*
+
 *   Deprecate `Rails::Rack::LogTailer` without replacement.
 
     *Rafael Mendonça França*
diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index 362713eb75..c5fd08e743 100644
--- a/railties/lib/rails/application.rb
+++ b/railties/lib/rails/application.rb
@@ -187,6 +187,38 @@ module Rails
       end
     end
 
+    # Convenience for loading config/foo.yml for the current Rails env.
+    #
+    # Example:
+    #
+    #     # config/exception_notification.yml:
+    #     production:
+    #       url: http://127.0.0.1:8080
+    #       namespace: my_app_production
+    #     development:
+    #       url: http://localhost:3001
+    #       namespace: my_app_development
+    #
+    #     # config/production.rb
+    #     MyApp::Application.configure do
+    #       config.middleware.use ExceptionNotifier, config_for(:exception_notification)
+    #     end
+    def config_for(name)
+      yaml = Pathname.new("#{paths["config"].existent.first}/#{name}.yml")
+
+      if yaml.exist?
+        require "yaml"
+        require "erb"
+        (YAML.load(ERB.new(yaml.read).result) || {})[Rails.env] || {}
+      else
+        raise "Could not load configuration. No such file - #{yaml}"
+      end
+    rescue Psych::SyntaxError => e
+      raise "YAML syntax error occurred while parsing #{yaml}. " \
+        "Please note that YAML must be consistently indented using spaces. Tabs are not allowed. " \
+        "Error: #{e.message}"
+    end
+
     # Stores some of the Rails initial environment parameters which
     # will be used by middlewares and engines to configure themselves.
     def env_config
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 2e056be561..e6e2c67826 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -989,5 +989,89 @@ module ApplicationTests
 
       assert_equal Rails.application.config.action_mailer.show_previews, true
     end
+
+    test "config_for loads custom configuration from yaml files" do
+      app_file 'config/custom.yml', <<-RUBY
+      development:
+        key: 'custom key'
+      RUBY
+
+      add_to_config <<-RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+
+      require "#{app_path}/config/environment"
+
+      assert_equal 'custom key', Rails.application.config.my_custom_config['key']
+    end
+
+    test "config_for raises an exception if the file does not exist" do
+      add_to_config <<-RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+
+      exception = assert_raises(RuntimeError) do
+        require "#{app_path}/config/environment"
+      end
+
+      assert_equal "Could not load configuration. No such file - #{app_path}/config/custom.yml", exception.message
+    end
+
+    test "config_for without the environment configured returns an empty hash" do
+      app_file 'config/custom.yml', <<-RUBY
+      test:
+        key: 'custom key'
+      RUBY
+
+      add_to_config <<-RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+      require "#{app_path}/config/environment"
+
+      assert_equal({}, Rails.application.config.my_custom_config)
+    end
+
+    test "config_for with empty file returns an empty hash" do
+      app_file 'config/custom.yml', <<-RUBY
+      RUBY
+
+      add_to_config <<-RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+      require "#{app_path}/config/environment"
+
+      assert_equal({}, Rails.application.config.my_custom_config)
+    end
+
+    test "config_for containing ERB tags should evaluate" do
+      app_file 'config/custom.yml', <<-RUBY
+      development:
+        key: <%= 'custom key' %>
+      RUBY
+
+      add_to_config <<-RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+      require "#{app_path}/config/environment"
+
+      assert_equal 'custom key', Rails.application.config.my_custom_config['key']
+    end
+
+    test "config_for with syntax error show a more descritive exception" do
+      app_file 'config/custom.yml', <<-RUBY
+      development:
+        key: foo:
+      RUBY
+
+      add_to_config <<-RUBY
+        config.my_custom_config = config_for('custom')
+      RUBY
+
+      exception = assert_raises(RuntimeError) do
+        require "#{app_path}/config/environment"
+      end
+
+      assert_match 'YAML syntax error occurred while parsing', exception.message
+    end
   end
 end