Add mixins folder

This moves several files to a new `mixins/` folder. I was going to add
some new macros, per [this comment][1], but thought it might clutter
things up a bit to put them in the root folder. I thought of adding a
`macros/` folder, but decided to emulate the [rubocop source][2]
instead.

[1]: #934 (comment)
[2]: https://github.com/rubocop-hq/rubocop/tree/master/lib/rubocop/cop/mixin

lib/rubocop-rspec.rb

@@ -12,17 +12,19 @@
 require_relative 'rubocop/rspec/wording'
 require_relative 'rubocop/rspec/language'
 require_relative 'rubocop/rspec/language/node_pattern'
-require_relative 'rubocop/rspec/top_level_group'
+
+require_relative 'rubocop/cop/rspec/mixin/top_level_group'
+require_relative 'rubocop/cop/rspec/mixin/variable'
+require_relative 'rubocop/cop/rspec/mixin/final_end_location'
+require_relative 'rubocop/cop/rspec/mixin/empty_line_separation'
+
 require_relative 'rubocop/rspec/concept'
 require_relative 'rubocop/rspec/example_group'
 require_relative 'rubocop/rspec/example'
 require_relative 'rubocop/rspec/hook'
-require_relative 'rubocop/rspec/variable'
 require_relative 'rubocop/cop/rspec/base'
 require_relative 'rubocop/rspec/align_let_brace'
 require_relative 'rubocop/rspec/factory_bot'
-require_relative 'rubocop/rspec/final_end_location'
-require_relative 'rubocop/rspec/empty_line_separation'
 require_relative 'rubocop/rspec/corrector/move_node'
 
 RuboCop::RSpec::Inject.defaults!

lib/rubocop/cop/rspec/describe_class.rb

@@ -35,7 +35,7 @@ module RSpec
       #   describe "A feature example", type: :feature do
       #   end
       class DescribeClass < Base
-        include RuboCop::RSpec::TopLevelGroup
+        include TopLevelGroup
 
         MSG = 'The first argument to describe should be '\
               'the class or module being tested.'

lib/rubocop/cop/rspec/describe_method.rb

@@ -17,7 +17,7 @@ module RSpec
       #   describe MyClass, '.my_class_method' do
       #   end
       class DescribeMethod < Base
-        include RuboCop::RSpec::TopLevelGroup
+        include TopLevelGroup
 
         MSG = 'The second argument to describe should be the method '\
               "being tested. '#instance' or '.class'."

lib/rubocop/cop/rspec/empty_line_after_example.rb

@@ -43,7 +43,7 @@ module RSpec
       #
       class EmptyLineAfterExample < Base
         extend AutoCorrector
-        include RuboCop::RSpec::EmptyLineSeparation
+        include EmptyLineSeparation
 
         MSG = 'Add an empty line after `%<example>s`.'
 

lib/rubocop/cop/rspec/empty_line_after_example_group.rb

@@ -25,7 +25,7 @@ module RSpec
       #
       class EmptyLineAfterExampleGroup < Base
         extend AutoCorrector
-        include RuboCop::RSpec::EmptyLineSeparation
+        include EmptyLineSeparation
 
         MSG = 'Add an empty line after `%<example_group>s`.'
 

lib/rubocop/cop/rspec/empty_line_after_final_let.rb

@@ -18,7 +18,7 @@ module RSpec
       #   it { does_something }
       class EmptyLineAfterFinalLet < Base
         extend AutoCorrector
-        include RuboCop::RSpec::EmptyLineSeparation
+        include EmptyLineSeparation
 
         MSG = 'Add an empty line after the last `%<let>s`.'
 

lib/rubocop/cop/rspec/empty_line_after_hook.rb

@@ -35,7 +35,7 @@ module RSpec
       #
       class EmptyLineAfterHook < Base
         extend AutoCorrector
-        include RuboCop::RSpec::EmptyLineSeparation
+        include EmptyLineSeparation
 
         MSG = 'Add an empty line after `%<hook>s`.'
 

lib/rubocop/cop/rspec/empty_line_after_subject.rb

@@ -16,7 +16,7 @@ module RSpec
       #   let(:foo) { bar }
       class EmptyLineAfterSubject < Base
         extend AutoCorrector
-        include RuboCop::RSpec::EmptyLineSeparation
+        include EmptyLineSeparation
 
         MSG = 'Add an empty line after `%<subject>s`.'
 

lib/rubocop/cop/rspec/file_path.rb

@@ -57,7 +57,7 @@ module RSpec
       #   my_class_spec.rb         # describe MyClass, '#method'
       #
       class FilePath < Base
-        include RuboCop::RSpec::TopLevelGroup
+        include TopLevelGroup
 
         MSG = 'Spec path should end with `%<suffix>s`.'
 

lib/rubocop/cop/rspec/instance_variable.rb

@@ -47,7 +47,7 @@ module RSpec
       #   end
       #
       class InstanceVariable < Base
-        include RuboCop::RSpec::TopLevelGroup
+        include TopLevelGroup
 
         MSG = 'Avoid instance variables – use let, ' \
               'a method call, or a local variable (if possible).'

lib/rubocop/cop/rspec/mixin/empty_line_separation.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Helps determine the offending location if there is not an empty line
+      # following the node. Allows comments to follow directly after.
+      module EmptyLineSeparation
+        include FinalEndLocation
+        include RangeHelp
+
+        def missing_separating_line_offense(node)
+          return if last_child?(node)
+
+          missing_separating_line(node) do |location|
+            msg = yield(node.method_name)
+            add_offense(location, message: msg) do |corrector|
+              corrector.insert_after(location.end, "\n")
+            end
+          end
+        end
+
+        def missing_separating_line(node)
+          line = final_end_location(node).line
+
+          line += 1 while comment_line?(processed_source[line])
+
+          return if processed_source[line].blank?
+
+          yield offending_loc(line)
+        end
+
+        def offending_loc(last_line)
+          offending_line = processed_source[last_line - 1]
+
+          content_length = offending_line.lstrip.length
+          start          = offending_line.length - content_length
+
+          source_range(processed_source.buffer,
+                       last_line, start, content_length)
+        end
+
+        def last_child?(node)
+          return true unless node.parent&.begin_type?
+
+          node.equal?(node.parent.children.last)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rspec/mixin/final_end_location.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Helps find the true end location of nodes which might contain heredocs.
+      module FinalEndLocation
+        def final_end_location(start_node)
+          heredoc_endings =
+            start_node.each_node(:str, :dstr, :xstr)
+              .select(&:heredoc?)
+              .map { |node| node.loc.heredoc_end }
+
+          [start_node.loc.end, *heredoc_endings].max_by(&:line)
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rspec/mixin/top_level_group.rb

@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Helper methods for top level example group cops
+      module TopLevelGroup
+        extend RuboCop::NodePattern::Macros
+        include RuboCop::RSpec::Language
+
+        def_node_matcher :example_or_shared_group?,
+                         (ExampleGroups::ALL + SharedGroups::ALL).block_pattern
+
+        def on_new_investigation
+          super
+
+          return unless root_node
+
+          top_level_groups.each do |node|
+            on_top_level_example_group(node) if example_group?(node)
+            on_top_level_group(node)
+          end
+        end
+
+        def top_level_groups
+          @top_level_groups ||=
+            top_level_nodes(root_node).select do |node|
+              example_or_shared_group?(node)
+            end
+        end
+
+        private
+
+        # Dummy methods to be overridden in the consumer
+        def on_top_level_example_group(_node); end
+
+        def on_top_level_group(_node); end
+
+        def top_level_group?(node)
+          top_level_groups.include?(node)
+        end
+
+        def top_level_nodes(node)
+          if node.nil?
+            []
+          elsif node.begin_type?
+            node.children
+          elsif node.module_type? || node.class_type?
+            top_level_nodes(node.body)
+          else
+            [node]
+          end
+        end
+
+        def root_node
+          processed_source.ast
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rspec/mixin/variable.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Helps check offenses with variable definitions
+      module Variable
+        include RuboCop::RSpec::Language
+        extend RuboCop::NodePattern::Macros
+
+        def_node_matcher :variable_definition?, <<~PATTERN
+          (send nil? #{(Helpers::ALL + Subject::ALL).node_pattern_union}
+            $({sym str dsym dstr} ...) ...)
+        PATTERN
+      end
+    end
+  end
+end

lib/rubocop/cop/rspec/multiple_describes.rb

@@ -23,7 +23,7 @@ module RSpec
       #     end
       #   end
       class MultipleDescribes < Base
-        include RuboCop::RSpec::TopLevelGroup
+        include TopLevelGroup
 
         MSG = 'Do not use multiple top-level example groups - '\
               'try to nest them.'

lib/rubocop/cop/rspec/multiple_memoized_helpers.rb

@@ -85,7 +85,7 @@ module RSpec
       #
       class MultipleMemoizedHelpers < Base
         include ConfigurableMax
-        include RuboCop::RSpec::Variable
+        include Variable
 
         MSG = 'Example group has too many memoized helpers [%<count>d/%<max>d]'
 

lib/rubocop/cop/rspec/nested_groups.rb

@@ -87,7 +87,7 @@ module RSpec
       #
       class NestedGroups < Base
         include ConfigurableMax
-        include RuboCop::RSpec::TopLevelGroup
+        include TopLevelGroup
 
         MSG = 'Maximum example group nesting exceeded [%<total>d/%<max>d].'
 

lib/rubocop/cop/rspec/subject_stub.rb

@@ -22,7 +22,7 @@ module RSpec
       #   end
       #
       class SubjectStub < Base
-        include RuboCop::RSpec::TopLevelGroup
+        include TopLevelGroup
 
         MSG = 'Do not stub methods of the object under test.'
 

lib/rubocop/cop/rspec/variable_definition.rb

@@ -24,7 +24,7 @@ module RSpec
       #   let('user_name') { 'Adam' }
       class VariableDefinition < Base
         include ConfigurableEnforcedStyle
-        include RuboCop::RSpec::Variable
+        include Variable
 
         MSG = 'Use %<style>s for variable names.'
 

lib/rubocop/cop/rspec/variable_name.rb

@@ -42,7 +42,7 @@ module RSpec
       class VariableName < Base
         include ConfigurableNaming
         include IgnoredPattern
-        include RuboCop::RSpec::Variable
+        include Variable
 
         MSG = 'Use %<style>s for variable names.'
 

lib/rubocop/rspec/corrector/move_node.rb

@@ -6,7 +6,7 @@ module Corrector
       # Helper methods to move a node
       class MoveNode
         include RuboCop::Cop::RangeHelp
-        include RuboCop::RSpec::FinalEndLocation
+        include RuboCop::Cop::RSpec::FinalEndLocation
 
         attr_reader :original, :corrector, :processed_source