Refine described_class inference further.

In the last commit, I made inner `describe SomeClass`
example groups get `SomeClass` as the described_class.
The logic confusingly allowed a `:described_class` metadata
key in an outer group take precedence, which meant that the
behavior depended on whether or not `described_class` was
referenced from the outer group.

This fixes that, making it work consistently:

- Use `:described_class` is present.
- Otherwise, use the group's `describe` arg
  (unless it's something like a string).
- If neither of those, look in the parent and
  recurse.

Author: myronmarston

lib/rspec/core/metadata.rb

@@ -148,9 +148,7 @@ def described_class
                 return value unless value.nil?
               end
             end
-          end
 
-          container_stack.each do |g|
             candidate = g[:description_args].first
             return candidate unless String === candidate || Symbol === candidate
           end

spec/rspec/core/example_group_spec.rb

@@ -482,16 +482,27 @@ def ascending_numbers
           expect(group.run).to be_truthy, "expected examples in group to pass"
         end
 
-        it "overrides the described class when a class is passed" do
-          value = nil
+        context "when a class is passed" do
+          def described_class_value
+            value = nil
+
+            ExampleGroup.describe(String) do
+              yield if block_given?
+              describe Array do
+                example { value = described_class }
+              end
+            end.run
 
-          ExampleGroup.describe(String) do
-            describe Array do
-              example { value = described_class }
-            end
-          end.run
+            value
+          end
+
+          it "overrides the described class" do
+            expect(described_class_value).to eq(Array)
+          end
 
-          expect(value).to eq(Array)
+          it "overrides the described class even when described_class is referenced in the outer group" do
+            expect(described_class_value { described_class }).to eq(Array)
+          end
         end
       end
 

spec/rspec/core/metadata_spec.rb

@@ -319,7 +319,7 @@ module Core
               child[:example_group][key] = Hash
 
               grandchild = Metadata.new(child)
-              grandchild.process(Array)
+              grandchild.process("sub context")
 
               expect(grandchild[:example_group][key]).to be(Hash)
               expect(child[:example_group][key]).to be(Hash)