Fix a regression in our metadata backwards compatibility

lib/rspec/core/metadata.rb

@@ -149,6 +149,11 @@ def ensure_valid_user_keys
       class ExampleHash < HashPopulator
         def self.create(group_metadata, user_metadata, description, block)
           example_metadata = group_metadata.dup
+          group_metadata = Hash.new(&ExampleGroupHash.backwards_compatibility_default_proc do |hash|
+            hash[:parent_example_group]
+          end)
+          group_metadata.update(example_metadata)
+
           example_metadata[:example_group] = group_metadata
           example_metadata.delete(:parent_example_group)
 
@@ -184,14 +189,18 @@ def self.create(parent_group_metadata, user_metadata, *args, &block)
         end
 
         def self.hash_with_backwards_compatibility_default_proc
-          Hash.new do |hash, key|
+          Hash.new(&backwards_compatibility_default_proc { |hash| hash })
+        end
+
+        def self.backwards_compatibility_default_proc(&example_group_selector)
+          Proc.new do |hash, key|
             case key
             when :example_group
               RSpec.deprecate("The `:example_group` key in an example group's metadata hash",
                               :replacement => "the example group's hash directly for the " +
                               "computed keys and `:parent_example_group` to access the parent " +
                               "example group metadata")
-              LegacyExampleGroupHash.new(hash)
+              LegacyExampleGroupHash.new(example_group_selector.call(hash))
             when :example_group_block
               RSpec.deprecate("`metadata[:example_group_block]`",
                               :replacement => "`metadata[:block]`")
@@ -370,7 +379,7 @@ class LegacyExampleGroupHash
 
       def initialize(metadata)
         @metadata = metadata
-        self[:example_group] = metadata[:parent_example_group]
+        self[:example_group] = metadata[:parent_example_group][:example_group]
       end
 
       def to_h

spec/rspec/core/metadata_spec.rb

@@ -117,6 +117,8 @@ def metadata_for(*args)
           end
 
           a[:description] = "new description"
+
+          pending "Cannot maintain this and provide full `:example_group` backwards compatibility (see GH #1490):("
           expect(b[:description]).to eq("new description")
         end
 
@@ -460,13 +462,30 @@ def value_for(*args)
               describe("nested") { child = metadata }
             end
 
-            expect(child[:example_group][:example_group]).to include(
+            expect(child[:example_group][:example_group].to_h).to include(
               :foo => 3,
               :description => "Object group",
               :line_number => parent_line
             )
           end
 
+          it "works properly with deep nesting" do
+            inner_metadata = nil
+
+            RSpec.describe "Level 1" do
+              describe "Level 2" do
+                describe "Level 3" do
+                  inner_metadata = example("Level 4").metadata
+                end
+              end
+            end
+
+            expect(inner_metadata[:description]).to eq("Level 4")
+            expect(inner_metadata[:example_group][:description]).to eq("Level 3")
+            expect(inner_metadata[:example_group][:example_group][:description]).to eq("Level 2")
+            expect(inner_metadata[:example_group][:example_group][:example_group][:description]).to eq("Level 1")
+          end
+
           it 'can mutate attributes when accessing them via [:example_group]' do
             meta = nil