LeakyConstantDeclaration - allow definitions on example group

Constant, classes, and modules that are defined on the example group do
not leak into the global namespace. While doing this may not be
a particularly good practice, it should ideally not result in
an offense.

The practice is described here: https://makandracards.com/makandra/47189-rspec-how-to-define-classes-for-specs#section-1-defining-the-constant-on-the-example-class

Author: naveg

lib/rubocop/cop/rspec/leaky_constant_declaration.rb

@@ -100,18 +100,21 @@ class LeakyConstantDeclaration < Base
 
         def on_casgn(node)
           return unless inside_describe_block?(node)
+          return if defined_on_example_group?(node)
 
           add_offense(node, message: MSG_CONST)
         end
 
         def on_class(node)
           return unless inside_describe_block?(node)
+          return if defined_on_example_group?(node)
 
           add_offense(node, message: MSG_CLASS)
         end
 
         def on_module(node)
           return unless inside_describe_block?(node)
+          return if defined_on_example_group?(node)
 
           add_offense(node, message: MSG_MODULE)
         end
@@ -121,6 +124,16 @@ def on_module(node)
         def inside_describe_block?(node)
           node.each_ancestor(:block).any?(&method(:spec_group?))
         end
+
+        def defined_on_example_group?(node)
+          if node.is_a?(RuboCop::AST::ClassNode) || node.is_a?(RuboCop::AST::ModuleNode)
+            node.loc.name.source.start_with?('self::')
+          elsif node.is_a?(RuboCop::AST::CasgnNode)
+            node.namespace&.self_type?
+          else
+            false
+          end
+        end
       end
     end
   end

spec/rubocop/cop/rspec/leaky_constant_declaration_spec.rb

@@ -31,6 +31,14 @@
       RUBY
     end
 
+    it 'ignores constant defined on the example group' do
+      expect_no_offenses(<<~RUBY)
+        describe SomeClass do
+          self::CONSTANT = "Accessible as self.class::CONSTANT".freeze
+        end
+      RUBY
+    end
+
     it 'ignores outside of example/shared group' do
       expect_no_offenses(<<~RUBY)
         factory :some_class do
@@ -60,7 +68,16 @@ def method
               end
             end
           end
-         end
+        end
+      RUBY
+    end
+
+    it 'ignores classes defined on the example group' do
+      expect_no_offenses(<<~RUBY)
+        describe SomeClass do
+          class self::DummyClass
+          end
+        end
       RUBY
     end
 
@@ -85,5 +102,14 @@ module DummyModule
         end
       RUBY
     end
+
+    it 'ignores modules defined on the example group' do
+      expect_no_offenses(<<~RUBY)
+        describe SomeClass do
+          module self::DummyModule
+          end
+        end
+      RUBY
+    end
   end
 end