Add a minimalist formatter (c/quickfix style output) (#2614)

* Add a minimalisr 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 similar 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 visually 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\ m
```

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 :MinimalFormatter,         'rspec/core/formatters/minimal_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 'm', 'minimal'
+        MinimalFormatter
       end
     end
 

lib/rspec/core/formatters/minimal_formatter.rb

@@ -0,0 +1,23 @@
+RSpec::Support.require_rspec_core "formatters/base_formatter"
+
+module RSpec
+  module Core
+    module Formatters
+      # @private
+      class MinimalFormatter < BaseFormatter
+        Formatters.register self, :example_failed, :dump_profile, :message
+
+        def example_failed(failure)
+          output.puts "#{failure.example.location}:#{failure.example.description}"
+        end
+
+        # Discard profile and messages
+        #
+        # These outputs are not really relevant in the context of this minimal
+        # formatter.
+        def dump_profile(_profile); end
+        def message(_message); 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',
+                  '  [m]inimal (suitable for editors integration)',
                   '  custom formatter class name') do |o|
           options[:formatters] ||= []
           options[:formatters] << [o]

spec/rspec/core/formatters/minimal_formatter_spec.rb

@@ -0,0 +1,19 @@
+require 'rspec/core/formatters/minimal_formatter'
+
+module RSpec::Core::Formatters
+  RSpec.describe MinimalFormatter do
+    include FormatterSupport
+
+    it 'produces the expected full output' do
+      output = run_example_specs_with_formatter('minimal')
+      expect(output).to eq(<<-EOS.gsub(/^\s+\|/, ''))
+        |./spec/rspec/core/resources/formatter_specs.rb:4:is marked as pending but passes
+        |./spec/rspec/core/resources/formatter_specs.rb:36:fails
+        |./spec/rspec/core/resources/formatter_specs.rb:40:fails twice
+        |./spec/rspec/core/resources/formatter_specs.rb:47:fails with a backtrace that has no file
+        |./spec/rspec/core/resources/formatter_specs.rb:53:fails with a backtrace containing an erb file
+        |./spec/rspec/core/resources/formatter_specs.rb:71:raises
+      EOS
+    end
+  end
+end