support custom formatter as --format option

lib/rspec/core/configuration.rb

@@ -151,13 +151,17 @@ def full_description=(description)
       end
 
       def formatter=(formatter_to_use)
-        formatter_class = case formatter_to_use.to_s
-        when 'd', 'doc', 'documentation', 's', 'n', 'spec', 'nested'
-          RSpec::Core::Formatters::DocumentationFormatter
-        when 'progress' 
-          RSpec::Core::Formatters::ProgressFormatter
-        else 
-          raise ArgumentError, "Formatter '#{formatter_to_use}' unknown - maybe you meant 'documentation' or 'progress'?."
+        if formatter_to_use.is_a?(Class)
+          formatter_class = formatter_to_use
+        else
+          formatter_class = case formatter_to_use.to_s
+          when 'd', 'doc', 'documentation', 's', 'n', 'spec', 'nested'
+            RSpec::Core::Formatters::DocumentationFormatter
+          when 'progress' 
+            RSpec::Core::Formatters::ProgressFormatter
+          else 
+            raise ArgumentError, "Formatter '#{formatter_to_use}' unknown - maybe you meant 'documentation' or 'progress'?."
+          end
         end
         self.formatter_class = formatter_class
       end

lib/rspec/core/option_parser.rb

@@ -43,7 +43,8 @@ def parser(options)
 
         parser.on('-f', '--format FORMATTER', 'Choose a formatter',
                 '  [p]rogress (default - dots)',
-                '  [d]ocumentation (group and example names)') do |o|
+                '  [d]ocumentation (group and example names)',
+                '  custom formatter class name') do |o|
           options[:formatter] = o
         end
 

spec/rspec/core/configuration_options_spec.rb

@@ -35,12 +35,16 @@ def options_from_args(*args)
     end
   end
 
-  describe  'formatter' do
+  describe  'format' do
     example '-f or --format with an argument should parse' do
       options_from_args('--format', 'd').should include(:formatter => 'd')
       options_from_args('-f', 'd').should include(:formatter => 'd')
       options_from_args('-fd').should include(:formatter => 'd')
     end
+
+    example "-f/--format can accept a class name" do
+      options_from_args('-fSome::Formatter::Class').should include(:formatter => 'Some::Formatter::Class')
+    end
   end
 
   describe 'profile_examples' do

spec/rspec/core/configuration_spec.rb

@@ -190,6 +190,12 @@ def that_thing
         config.formatter = 'documentation'
         config.formatter.should be_an_instance_of(Formatters::DocumentationFormatter)
       end
+
+      it "sets a formatter based on its class" do
+        formatter_class = Class.new(Formatters::BaseTextFormatter)
+        config.formatter = formatter_class
+        config.formatter.should be_an_instance_of(formatter_class)
+      end
 
       it "raises ArgumentError if formatter is unknown" do
         lambda { config.formatter = :progresss }.should raise_error(ArgumentError)