describe at runtime configuration of global exposure

features/configuration/enable_global_dsl.feature

@@ -14,31 +14,25 @@ Feature: Global namespace DSL
    Then the output should contain "1 example, 0 failures"
 
   Scenario: when exposing globally is disabled top level dsl no longer works
-    Given a file named "config.rb" with:
-      """ruby
-        RSpec.configure { |c| c.expose_globally = false }
-      """
     Given a file named "spec/example_spec.rb" with:
       """ruby
+      RSpec.configure { |c| c.expose_globally = false }
       describe "specs here" do
         it "passes" do
         end
       end
       """
-   When I run `rspec -r ./config.rb`
+   When I run `rspec`
    Then the output should contain "undefined method `describe'"
 
   Scenario: regardless of setting
-    Given a file named "config.rb" with:
-      """ruby
-        RSpec.configure { |c| c.expose_globally = true }
-      """
     Given a file named "spec/example_spec.rb" with:
       """ruby
+      RSpec.configure { |c| c.expose_globally = true }
       RSpec.describe "specs here" do
         it "passes" do
         end
       end
       """
-   When I run `rspec -r ./config.rb`
+   When I run `rspec`
    Then the output should contain "1 example, 0 failures"

lib/rspec/core/dsl.rb

@@ -18,6 +18,47 @@ def self.describe(*args, &example_group_block)
 
   module Core
     module DSL
+
+      class << self
+        # @private
+        attr_accessor :top_level
+      end
+
+      # @private
+      def self.exposed_globally?
+        @exposed_globally ||= false
+      end
+
+      # Add's the describe method to Module and the top level binding
+      def self.expose_globally!
+        return if exposed_globally?
+
+        to_define = proc do
+          def describe(*args, &block)
+            ::RSpec.describe(*args, &block)
+          end
+        end
+
+        top_level.instance_eval(&to_define)
+        Module.class_exec(&to_define)
+        @exposed_globally = true
+      end
+
+      def self.remove_globally!
+        return unless exposed_globally?
+
+        to_undefine = proc do
+          undef describe
+        end
+
+        top_level.instance_eval(&to_undefine)
+        Module.class_exec(&to_undefine)
+        @exposed_globally = false
+      end
+
     end
   end
 end
+
+# cature main without an eval
+::RSpec::Core::DSL.top_level = self

lib/rspec/core/shared_example_group.rb

@@ -56,6 +56,35 @@ def shared_example_groups
           end
         end
 
+        # @private
+        def self.exposed_globally?
+          @exposed_globally ||= false
+        end
+
+        def self.expose_globally!
+          return if exposed_globally?
+
+          Core::DSL.top_level.instance_eval(&definitions)
+          Module.class_exec(&definitions)
+          @exposed_globally = true
+        end
+
+        def self.remove_globally!
+          return unless exposed_globally?
+
+          to_undefine = proc do
+            undef shared_examples
+            undef shared_context
+            undef share_examples_for
+            undef shared_examples_for
+            undef shared_example_groups
+          end
+
+          Core::DSL.top_level.instance_eval(&to_undefine)
+          Module.class_exec(&to_undefine)
+          @exposed_globally = false
+        end
+
       end
 
       def self.registry