Fix how RSpec::Matchers is included in RSpec::Core::Example group to prevent SystemStackError on 1.9.

Author: myronmarston

lib/rspec/core/command_line.rb

@@ -16,8 +16,6 @@ def run(err, out)
         @configuration.output_stream ||= out
         @options.configure(@configuration)
         @configuration.load_spec_files
-        @configuration.configure_mock_framework
-        @configuration.configure_expectation_framework
         @world.announce_inclusion_filter
         @world.announce_exclusion_filter
 

lib/rspec/core/example_group.rb

@@ -151,7 +151,24 @@ def self.top_level?
         @top_level ||= superclass == ExampleGroup
       end
 
+      def self.ensure_example_groups_are_configured
+        unless @example_groups_configured
+          RSpec.configuration.configure_mock_framework
+          RSpec.configuration.configure_expectation_framework
+          @example_groups_configured = true
+        end
+      end
+
       def self.set_it_up(*args)
+        # Ruby 1.9 has a bug that can lead to infinite recursion and a
+        # SystemStackError if you include a module in a superclass after
+        # including it in a subclass: https://gist.github.com/845896
+        # To prevent this, we must include any modules in RSpec::Core::ExampleGroup
+        # before users create example groups and have a chance to include
+        # the same module in a subclass of RSpec::Core::ExampleGroup.
+        # So we need to configure example groups here.
+        ensure_example_groups_are_configured
+
         symbol_description = args.shift if args.first.is_a?(Symbol)
         args << build_metadata_hash_from(args)
         args.unshift(symbol_description) if symbol_description

spec/rspec/core/command_line_spec.rb

@@ -50,8 +50,6 @@ module RSpec::Core
         config.stub(:run_hook)
 
         config.should_receive(:load_spec_files)
-        config.should_receive(:configure_mock_framework)
-        config.should_receive(:configure_expectation_framework)
 
         world.should_receive(:announce_inclusion_filter)
         world.should_receive(:announce_exclusion_filter)

spec/rspec/core/rspec_matchers_spec.rb

@@ -0,0 +1,45 @@
+require 'spec_helper'
+
+module RSpec::Matchers
+  def __method_with_super
+    super
+  end
+
+  module ModThatIncludesMatchers
+    include RSpec::Matchers
+  end
+
+  RSpec.configure do |c|
+    c.include RSpec::Matchers, :include_rspec_matchers => true
+    c.include ModThatIncludesMatchers, :include_mod_that_includes_rspec_matchers => true
+  end
+
+  describe self do
+    shared_examples_for "a normal module with a method that supers" do
+      it "raises the expected error (and not SystemStackError)" do
+        expect { __method_with_super }.to raise_error(NoMethodError) # there is no __method_with_super in an ancestor
+      end
+    end
+
+    it_behaves_like "a normal module with a method that supers"
+
+    context "when RSpec::Matchers has been included in an example group" do
+      include RSpec::Matchers
+      it_behaves_like "a normal module with a method that supers"
+    end
+
+    context "when a module that includes RSpec::Matchers has been included in an example group" do
+      include RSpec::Matchers::ModThatIncludesMatchers
+      it_behaves_like "a normal module with a method that supers"
+    end
+
+    context "when RSpec::Matchers is included via configuration", :include_rspec_matchers => true do
+      it_behaves_like "a normal module with a method that supers"
+    end
+
+    context "when RSpec::Matchers is included in a module that is included via configuration", :include_mod_that_includes_rspec_matchers => true do
+      it_behaves_like "a normal module with a method that supers"
+    end
+  end
+end
+