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:
 

benchmarks/ripper.rb

@@ -0,0 +1,44 @@
+require 'benchmark/ips'
+require 'ripper'
+
+ruby_version = defined?(JRUBY_VERSION) ? JRUBY_VERSION : RUBY_VERSION
+puts "#{RUBY_ENGINE} #{ruby_version}"
+
+source = File.read(__FILE__)
+
+Benchmark.ips do |x|
+  x.report("Ripper") do
+    Ripper.sexp(source)
+    Ripper.lex(source)
+  end
+end
+
+__END__
+
+ruby 1.9.3
+Calculating -------------------------------------
+              Ripper   284.000  i/100ms
+
+ruby 2.2.3
+Calculating -------------------------------------
+              Ripper   320.000  i/100ms
+
+jruby 1.7.5
+Calculating -------------------------------------
+              Ripper    24.000  i/100ms
+
+jruby 1.7.13
+Calculating -------------------------------------
+              Ripper    25.000  i/100ms
+
+jruby 1.7.14
+Calculating -------------------------------------
+              Ripper   239.000  i/100ms
+
+jruby 1.7.22
+Calculating -------------------------------------
+              Ripper   231.000  i/100ms
+
+jruby 9.0.1.0
+Calculating -------------------------------------
+              Ripper   218.000  i/100ms

lib/rspec/support/ruby_features.rb

@@ -1,4 +1,5 @@
 require 'rbconfig'
+RSpec::Support.require_rspec_support "version_checker"
 
 module RSpec
   module Support
@@ -65,6 +66,29 @@ def supports_exception_cause?
         end
       end
 
+      UnsupportedVersionError = Class.new(StandardError)
+
+      begin
+        VersionChecker.new('Ruby', RUBY_VERSION, '1.9.0').check_version!
+
+        if Ruby.jruby?
+          # JRuby 1.7.5 - 1.7.13 actually supports Ripper but it's too slow.
+          # See benchmarks/ripper.rb.
+          VersionChecker.new('JRuby', JRUBY_VERSION, '1.7.14').check_version!
+
+          # Ripper on JRuby 9.0.0.0 reports wrong line number.
+          raise UnsupportedVersionError if JRUBY_VERSION.start_with?('9.')
+        end
+
+        def ripper_supported?
+          true
+        end
+      rescue LibraryVersionTooLowError, UnsupportedVersionError
+        def ripper_supported?
+          false
+        end
+      end
+
       if Ruby.mri?
         def kw_args_supported?
           RUBY_VERSION >= '2.0.0'

spec/rspec/support/ruby_features_spec.rb

@@ -81,6 +81,57 @@ module Support
           expect(RubyFeatures.caller_locations_supported?).to eq(RUBY_VERSION >= '2.0.0')
         end
       end
+
+      describe "#ripper_supported?" do
+        it 'does not load Ripper' do
+          expect { RubyFeatures.ripper_supported? }.not_to change { defined?(Ripper) }
+        end
+
+        describe 'Ripper' do
+          let(:line_number) do
+            token = tokens.first
+            location = token.first
+            location.first
+          end
+
+          let(:tokens) do
+            require 'ripper'
+            ::Ripper.lex('foo')
+          end
+
+          if !defined?(RUBY_ENGINE) || RUBY_ENGINE == 'ruby'
+            context 'on MRI' do
+              context '1.8.x', :if => RUBY_VERSION.start_with?('1.8.') do
+                it 'is not supported' do
+                  expect { tokens }.to raise_error(LoadError)
+                end
+              end
+
+              context '1.9.x or later', :if => RUBY_VERSION >= '1.9' do
+                it 'is supported' do
+                  expect(line_number).to eq(1)
+                end
+              end
+            end
+          end
+
+          if defined?(JRUBY_VERSION)
+            context 'on JRuby' do
+              context '1.7.x', :if => JRUBY_VERSION.start_with?('1.7.') do
+                it 'is supported' do
+                  expect(line_number).to eq(1)
+                end
+              end
+
+              context '9.x.x.x', :if => JRUBY_VERSION.start_with?('9.') do
+                it 'reports wrong line number' do
+                  expect(line_number).to eq(2)
+                end
+              end
+            end
+          end
+        end
+      end
     end
   end
 end