Make described_class to return innermost described class.

It used to return the outermost described class. It doesn't
happen very often that there is more than one class being
described in the set of nested example groups (and we
generally recommend against it), but this was surprising
behavior to me.

Fixes #1114.

Author: myronmarston

Changelog.md

@@ -1,6 +1,12 @@
 ### 3.0.0.rc1 Development
 [Full Changelog](http://github.com/rspec/rspec-core/compare/v3.0.0.beta2...master)
 
+Breaking Changes for 3.0.0:
+
+* Change `described_class` so that in a nested group like `describe
+  MyClass`, it returns `MyClass` rather than the outer group's described
+  class. (Myron Marston)
+
 Enhancements:
 
 * Add `config.default_formatter` attribute, which can be used to set a

features/subject/implicit_subject.feature

@@ -33,7 +33,7 @@ Feature: implicitly defined subject
     When I run `rspec nested_subject_spec.rb`
     Then the examples should all pass
 
-  Scenario: subject in a nested group with a different class (outermost wins)
+  Scenario: subject in a nested group with a different class (innermost wins)
     Given a file named "nested_subject_spec.rb" with:
       """ruby
       class ArrayWithOneElement < Array
@@ -46,14 +46,8 @@ Feature: implicitly defined subject
       describe Array do
         describe ArrayWithOneElement do
           context "referenced as subject" do
-            it "should be empty (because it is the Array declared at the top)" do
-              expect(subject).to be_empty
-            end
-          end
-
-          context "created in the example" do
-            it "should not be empty" do
-              expect(ArrayWithOneElement.new).not_to be_empty
+            it "contains one element" do
+              expect(subject).to include("first element")
             end
           end
         end

lib/rspec/core/metadata.rb

@@ -150,7 +150,7 @@ def described_class
             end
           end
 
-          container_stack.reverse.each do |g|
+          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

@@ -472,7 +472,7 @@ def ascending_numbers
       context "in a nested group" do
         it "inherits the described class/module from the outer group" do
           group = ExampleGroup.describe(String) do
-            describe Array do
+            describe "nested" do
               example "describes is String" do
                 expect(described_class).to eq(String)
               end
@@ -481,6 +481,18 @@ 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
+
+          ExampleGroup.describe(String) do
+            describe Array do
+              example { value = described_class }
+            end
+          end.run
+
+          expect(value).to eq(Array)
+        end
       end
 
       context "for `describe(SomeClass)` within a `describe 'some string' group" do
@@ -1111,8 +1123,8 @@ def extract_execution_results(group)
     describe Object, "describing nested example_groups", :little_less_nested => 'yep' do
 
       describe "A sample nested group", :nested_describe => "yep" do
-        it "sets the described class to the described class of the outer most group" do |ex|
-          expect(ex.example_group.described_class).to eq(ExampleGroup)
+        it "sets the described class to the nearest described class" do |ex|
+          expect(ex.example_group.described_class).to eq(Object)
         end
 
         it "sets the description to 'A sample nested describe'" do |ex|

spec/rspec/core/metadata_spec.rb

@@ -290,32 +290,32 @@ module Core
           end
 
           context "in a nested group" do
-            it "returns the parent group's described class" do
-              sm = Metadata.new
-              sm.process(String)
+            it "inherits the parent group's described class" do
+              parent = Metadata.new
+              parent.process(Hash)
 
-              m = Metadata.new(sm)
-              m.process(Array)
+              child = Metadata.new(parent)
+              child.process("sub context")
 
-              expect(m[:example_group][key]).to be(String)
+              expect(child[:example_group][key]).to be(Hash)
             end
 
-            it "returns own described class if parent doesn't have one" do
-              sm = Metadata.new
-              sm.process("foo")
+            it "sets the described class when passing a class" do
+              parent = Metadata.new
+              parent.process(String)
 
-              m = Metadata.new(sm)
-              m.process(Array)
+              child = Metadata.new(parent)
+              child.process(Array)
 
-              expect(m[:example_group][key]).to be(Array)
+              expect(child[:example_group][key]).to be(Array)
             end
 
-            it "can override a parent group's described class" do
+            it "can override a parent group's described class using metdata" do
               parent = Metadata.new
               parent.process(String)
 
               child = Metadata.new(parent)
-              child.process(Fixnum)
+              child.process("sub context")
               child[:example_group][key] = Hash
 
               grandchild = Metadata.new(child)