Remove 1.9 SystemStackError workaround

This basically reverts this commit
622a4b7
that works around a Ruby 1.9 bug http://bugs.ruby-lang.org/issues/3351

Also, it removes 'when user did not configure expectation framework' and
'when user did not configure mock framework' examples, since
mock/expectation frameworks are immediately configured on World
creation, and if user did not configure them, they both default to
`:rspec`.

No checks for defined example groups are necessary anymore.

Author: pirj

lib/rspec/core/configuration.rb

@@ -54,9 +54,6 @@ class Configuration
       Readers = Module.new
       include Readers
 
-      # @private
-      class MustBeConfiguredBeforeExampleGroupsError < StandardError; end
-
       # @private
       def self.define_reader(name)
         Readers.class_eval do
@@ -776,14 +773,6 @@ def mock_with(framework)
             RSpec::Core::MockingAdapters.const_get(const_name)
           end
 
-        new_name, old_name = [framework_module, @mock_framework].map do |mod|
-          mod.respond_to?(:framework_name) ? mod.framework_name : :unnamed
-        end
-
-        unless new_name == old_name
-          assert_no_example_groups_defined(:mock_framework)
-        end
-
         if block_given?
           raise "#{framework_module} must respond to `configuration` so that " \
                 "mock_with can yield it." unless framework_module.respond_to?(:configuration)
@@ -859,10 +848,6 @@ def expect_with(*frameworks)
           end
         end
 
-        if (modules - @expectation_frameworks).any?
-          assert_no_example_groups_defined(:expect_with)
-        end
-
         if block_given?
           raise "expect_with only accepts a block with a single argument. " \
                 "Call expect_with #{modules.length} times, " \
@@ -1615,6 +1600,9 @@ def load_spec_files
           loaded_spec_files << file
         end
 
+        configure_mock_framework
+        configure_expectation_framework
+
         @spec_files_loaded = true
       end
 
@@ -2243,15 +2231,6 @@ def define_built_in_hooks
         end
       end
 
-      def assert_no_example_groups_defined(config_option)
-        return unless world.example_groups.any?
-
-        raise MustBeConfiguredBeforeExampleGroupsError.new(
-          "RSpec's #{config_option} configuration option must be configured before " \
-          "any example groups are defined, but you have already defined a group."
-        )
-      end
-
       def output_wrapper
         @output_wrapper ||= OutputWrapper.new(output_stream)
       end

lib/rspec/core/example_group.rb

@@ -408,16 +408,6 @@ def self.subclass(parent, description, args, registration_collection, &example_g
 
       # @private
       def self.set_it_up(description, args, registration_collection, &example_group_block)
-        # 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
-
         # Register the example with the group before creating the metadata hash.
         # This is necessary since creating the metadata hash triggers
         # `when_first_matching_example_defined` callbacks, in which users can
@@ -514,17 +504,6 @@ def self.top_level?
         superclass == ExampleGroup
       end
 
-      # @private
-      def self.ensure_example_groups_are_configured
-        unless defined?(@@example_groups_configured)
-          RSpec.configuration.configure_mock_framework
-          RSpec.configuration.configure_expectation_framework
-          # rubocop:disable Style/ClassVars
-          @@example_groups_configured = true
-          # rubocop:enable Style/ClassVars
-        end
-      end
-
       # @private
       def self.before_context_ivars
         @before_context_ivars ||= {}

spec/rspec/core/configuration_spec.rb

@@ -355,28 +355,10 @@ def mod.configuration; @config ||= Struct.new(:custom_setting).new; end
       context 'when there are already some example groups defined' do
         before { allow(RSpec::Support).to receive(:require_rspec_core) }
 
-        it 'raises an error since this setting must be applied before any groups are defined' do
+        it 'does not raise an error' do
           allow(RSpec.world).to receive(:example_groups).and_return([double.as_null_object])
           class_double("RSpec::Core::MockingAdapters::Mocha", :framework_name => :mocha).as_stubbed_const
 
-          expect {
-            config.mock_with :mocha
-          }.to raise_error(/must be configured before any example groups are defined/)
-        end
-
-        it 'does not raise an error if the default `mock_with :rspec` is re-configured' do
-          config.mock_framework # called by RSpec when configuring the first example group
-          allow(RSpec.world).to receive(:example_groups).and_return([double.as_null_object])
-          config.mock_with :rspec
-        end
-
-        it 'does not raise an error if re-setting the same config' do
-          class_double("RSpec::Core::MockingAdapters::Mocha", :framework_name => :mocha).as_stubbed_const
-
-          groups = []
-          allow(RSpec.world).to receive_messages(:example_groups => groups)
-          config.mock_with :mocha
-          groups << double.as_null_object
           config.mock_with :mocha
         end
       end
@@ -487,26 +469,10 @@ def stub_expectation_adapters
       end
 
       context 'when there are already some example groups defined' do
-        it 'raises an error since this setting must be applied before any groups are defined' do
-          allow(RSpec.world).to receive(:example_groups).and_return([double.as_null_object])
-          expect {
-            config.expect_with :rspec
-          }.to raise_error(/must be configured before any example groups are defined/)
-        end
-
-        it 'does not raise an error if the default `expect_with :rspec` is re-configured' do
-          config.expectation_frameworks # called by RSpec when configuring the first example group
+        it 'does not raise an error' do
           allow(RSpec.world).to receive(:example_groups).and_return([double.as_null_object])
           config.expect_with :rspec
         end
-
-        it 'does not raise an error if re-setting the same config' do
-          groups = []
-          allow(RSpec.world).to receive_messages(:example_groups => groups)
-          config.expect_with :minitest
-          groups << double.as_null_object
-          config.expect_with :minitest
-        end
       end
     end
 
@@ -2768,52 +2734,6 @@ def in_fully_monkey_patched_rspec_environment
           }.to change { Marshal.respond_to?(:dump_with_rspec_mocks) }.from(true).to(false)
         end
       end
-
-      context 'when user did not configure mock framework' do
-        def emulate_not_configured_mock_framework
-          in_fully_monkey_patched_rspec_environment do
-            allow(config).to receive(:rspec_mocks_loaded?).and_return(false, true)
-            config.instance_variable_set :@mock_framework, nil
-            ExampleGroup.send :remove_class_variable, :@@example_groups_configured
-
-            yield
-          end
-        end
-
-        it 'disables monkey patching after example groups being configured' do
-          emulate_not_configured_mock_framework do
-            obj = Object.new
-            config.disable_monkey_patching!
-
-            expect {
-              ExampleGroup.ensure_example_groups_are_configured
-            }.to change { obj.respond_to?(:should_receive) }.from(true).to(false)
-          end
-        end
-      end
-
-      context 'when user did not configure expectation framework' do
-        def emulate_not_configured_expectation_framework
-          in_fully_monkey_patched_rspec_environment do
-            allow(config).to receive(:rspec_expectations_loaded?).and_return(false, true)
-            config.instance_variable_set :@expectation_frameworks, []
-            ExampleGroup.send :remove_class_variable, :@@example_groups_configured
-
-            yield
-          end
-        end
-
-        it 'disables monkey patching after example groups being configured' do
-          emulate_not_configured_expectation_framework do
-            obj = Object.new
-            config.disable_monkey_patching!
-
-            expect {
-              ExampleGroup.ensure_example_groups_are_configured
-            }.to change { obj.respond_to?(:should) }.from(true).to(false)
-          end
-        end
-      end
     end
 
     describe 'recording spec start time (for measuring load)' do