Add RubyFeatures.ripper_supported?

Author: yujinakayama

Changelog.md

@@ -4,6 +4,7 @@ Enhancements:
 
 * Improve formatting of `Delegator` based objects (e.g. `SimpleDelgator`) in
   failure messages and diffs. (Andrew Horner, #215)
+* Add `Ripper` support detection. (Yuji Nakayama, #245)
 
 Bug Fixes:
 

lib/rspec/support/ruby_features.rb

@@ -65,6 +65,12 @@ def supports_exception_cause?
         end
       end
 
+      def ripper_supported?
+        # JRuby supports Ripper but it seems to be unstable
+        # and also reports wrong line number on JRuby 9.0.0.0.
+        defined?(RUBY_ENGINE) && RUBY_ENGINE == 'ruby' && RUBY_VERSION >= '1.9.2'
+      end
+
       if Ruby.mri?
         def kw_args_supported?
           RUBY_VERSION >= '2.0.0'

spec/rspec/support/ruby_features_spec.rb

@@ -81,6 +81,12 @@ module Support
           expect(RubyFeatures.caller_locations_supported?).to eq(RUBY_VERSION >= '2.0.0')
         end
       end
+
+      specify "#ripper_supported? exists" do
+        RubyFeatures.ripper_supported?
+        # Ensure .ripper_supported? does not load Ripper.
+        expect { ::Ripper }.to raise_error(NameError)
+      end
     end
   end
 end