Add a simple C formatter

This formatter outputs failures in a similar fashion to the C compiler
— file:line:message — allowing straightforward integration with text
editors like vim and without adding extra dependencies to the project
(relying on the quickfix-window from vim or simlar feature for other
editors).

One can configure his editor with the following line (vim) and start
jumping between failures using the regular editor keybindings, without
having to visualy parse the output from rspec to find out the file and
line number he want to reach:

```vim
autocmd FileType ruby set makeprg=bundle\ exec\ rspec\ --format\ c
```

Author: smortex

lib/rspec/core/formatters.rb

@@ -74,6 +74,7 @@ module RSpec::Core::Formatters
   autoload :JsonFormatter,            'rspec/core/formatters/json_formatter'
   autoload :BisectDRbFormatter,       'rspec/core/formatters/bisect_drb_formatter'
   autoload :ExceptionPresenter,       'rspec/core/formatters/exception_presenter'
+  autoload :CFormatter,               'rspec/core/formatters/c_formatter'
 
   # Register the formatter class
   # @param formatter_class [Class] formatter class to register
@@ -212,6 +213,8 @@ def built_in_formatter(key)
         JsonFormatter
       when 'bisect-drb'
         BisectDRbFormatter
+      when 'c'
+        CFormatter
       end
     end
 

lib/rspec/core/formatters/c_formatter.rb

@@ -0,0 +1,18 @@
+RSpec::Support.require_rspec_core "formatters/base_formatter"
+
+module RSpec
+  module Core
+    module Formatters
+      # @private
+      class CFormatter < BaseFormatter
+        Formatters.register self, :example_failed, :dump_profile
+
+        def example_failed(failure)
+          output.puts "#{failure.example.metadata[:location]}:#{failure.example.metadata[:description]}"
+        end
+
+        def dump_profile(_profile); end
+      end
+    end
+  end
+end

lib/rspec/core/option_parser.rb

@@ -112,6 +112,7 @@ def parser(options)
                   '  [d]ocumentation (group and example names)',
                   '  [h]tml',
                   '  [j]son',
+                  '  c (minimalist output suitable for editors integration)',
                   '  custom formatter class name') do |o|
           options[:formatters] ||= []
           options[:formatters] << [o]