Add some missing keys to RESERVED_KEYS.

…and add a spec enforcing that it is always up-to-date.

lib/rspec/core/metadata.rb

@@ -322,6 +322,8 @@ def full_description
       # @private
       RESERVED_KEYS = [
         :description,
+        :description_args,
+        :described_class,
         :example_group,
         :parent_example_group,
         :execution_result,
@@ -332,7 +334,8 @@ def full_description
         :line_number,
         :location,
         :scoped_id,
-        :block
+        :block,
+        :shared_group_inclusion_backtrace
       ]
     end
 

spec/rspec/core/metadata_spec.rb

@@ -31,6 +31,15 @@ module Core
 
       end
 
+      specify 'RESERVED_KEYS contains all keys assigned by RSpec (and vice versa)' do
+        group        = RSpec.describe("group")
+        example      = group.example("example") { }
+        nested_group = group.describe("nested")
+
+        assigned_keys = group.metadata.keys | example.metadata.keys | nested_group.metadata.keys
+        expect(RSpec::Core::Metadata::RESERVED_KEYS).to match_array(assigned_keys)
+      end
+
       context "when created" do
         Metadata::RESERVED_KEYS.each do |key|
           it "prohibits :#{key} as a hash key for an example group" do