Introduce force framework and convert VariableInspector into a force

The force framework allows cops to share common logic and reduce wasted
CPU power by module mixins. A force implements custom processing and
invokes some hooks in cops that belong to the force.

lib/rubocop.rb

@@ -33,16 +33,17 @@
 require 'rubocop/cop/cop'
 require 'rubocop/cop/commissioner'
 require 'rubocop/cop/corrector'
+require 'rubocop/cop/force'
 require 'rubocop/cop/team'
 require 'rubocop/cop/severity'
 
-require 'rubocop/cop/variable_inspector'
-require 'rubocop/cop/variable_inspector/locatable'
-require 'rubocop/cop/variable_inspector/variable'
-require 'rubocop/cop/variable_inspector/assignment'
-require 'rubocop/cop/variable_inspector/reference'
-require 'rubocop/cop/variable_inspector/scope'
-require 'rubocop/cop/variable_inspector/variable_table'
+require 'rubocop/cop/variable_force'
+require 'rubocop/cop/variable_force/locatable'
+require 'rubocop/cop/variable_force/variable'
+require 'rubocop/cop/variable_force/assignment'
+require 'rubocop/cop/variable_force/reference'
+require 'rubocop/cop/variable_force/scope'
+require 'rubocop/cop/variable_force/variable_table'
 
 require 'rubocop/cop/mixin/annotation_comment'
 require 'rubocop/cop/mixin/array_syntax'

lib/rubocop/cop/commissioner.rb

@@ -28,8 +28,9 @@ def self.call_super(callback)
         end
       end
 
-      def initialize(cops, options = {})
+      def initialize(cops, forces, options = {})
         @cops = cops
+        @forces = forces
         @options = options
         reset_errors
       end
@@ -52,7 +53,8 @@ def #{callback}(node)
       def investigate(processed_source)
         reset_errors
         prepare(processed_source)
-        invoke_cops_callback(processed_source)
+        invoke_custom_processing(@cops, processed_source)
+        invoke_custom_processing(@forces, processed_source)
         process(processed_source.ast) if processed_source.ast
         @cops.each_with_object([]) do |cop, offenses|
           filename = processed_source.buffer.name
@@ -72,18 +74,19 @@ def prepare(processed_source)
         @cops.each { |cop| cop.processed_source = processed_source }
       end
 
-      # There are cops that require their own custom processing.
+      # There are cops/forces that require their own custom processing.
       # If they define the #investigate method, all input parameters passed
       # to the commissioner will be passed to the cop too in order to do
       # its own processing.
-      def invoke_cops_callback(processed_source)
-        @cops.each do |cop|
+      def invoke_custom_processing(cops_or_forces, processed_source)
+        cops_or_forces.each do |cop|
           next unless cop.respond_to?(:investigate)
 
-          filename = processed_source.buffer.name
-
-          # ignore files that are of no interest to the cop in question
-          next unless cop.relevant_file?(filename)
+          if cop.respond_to?(:relevant_file?)
+            # ignore files that are of no interest to the cop in question
+            filename = processed_source.buffer.name
+            next unless cop.relevant_file?(filename)
+          end
 
           with_cop_error_handling(cop) do
             cop.investigate(processed_source)

lib/rubocop/cop/cop.rb

@@ -88,6 +88,10 @@ def initialize(config = nil, options = nil)
         @corrections = []
       end
 
+      def join_force?(force_class)
+        false
+      end
+
       def cop_config
         @config.for_cop(self)
       end

lib/rubocop/cop/force.rb

@@ -0,0 +1,41 @@
+# encoding: utf-8
+
+module Rubocop
+  module Cop
+    # A scaffold for concrete forces.
+    class Force
+      attr_reader :cops
+
+      def self.all
+        @all ||= []
+      end
+
+      def self.inherited(subclass)
+        all << subclass
+      end
+
+      def self.force_name
+        name.split('::').last
+      end
+
+      def initialize(cops)
+        @cops = cops
+      end
+
+      def name
+        self.class.force_name
+      end
+
+      def run_hook(method_name, *args)
+        cops.each do |cop|
+          next unless cop.respond_to?(method_name)
+          cop.send(method_name, *args)
+        end
+      end
+
+      def investigate(processed_source)
+        # Do custom processing and invoke #run_hook at arbitrary timing.
+      end
+    end
+  end
+end

lib/rubocop/cop/lint/shadowing_outer_local_variable.rb

@@ -8,15 +8,13 @@ module Lint
       # This is a mimic of the warning
       # "shadowing outer local variable - foo" from `ruby -cw`.
       class ShadowingOuterLocalVariable < Cop
-        include VariableInspector
-
         MSG = 'Shadowing outer local variable - `%s`'
 
-        def investigate(processed_source)
-          inspect_variables(processed_source.ast)
+        def join_force?(force_class)
+          force_class == VariableForce
         end
 
-        def before_declaring_variable(variable)
+        def before_declaring_variable(variable, variable_table)
           return if variable.name.to_s.start_with?('_')
 
           outer_local_variable = variable_table.find_variable(variable.name)

lib/rubocop/cop/lint/useless_assignment.rb

@@ -13,15 +13,13 @@ module Lint
       # reassignments and properly handles varied cases such as branch, loop,
       # rescue, ensure, etc.
       class UselessAssignment < Cop
-        include VariableInspector
-
         MSG = 'Useless assignment to variable - %s'
 
-        def investigate(processed_source)
-          inspect_variables(processed_source.ast)
+        def join_force?(force_class)
+          force_class == VariableForce
         end
 
-        def after_leaving_scope(scope)
+        def after_leaving_scope(scope, variable_table)
           scope.variables.each_value do |variable|
             check_for_unused_assignments(variable)
             check_for_unused_block_local_variable(variable)

lib/rubocop/cop/team.rb

@@ -32,7 +32,7 @@ def inspect_file(processed_source)
           return Lint::Syntax.offenses_from_diagnostics(diagnostics)
         end
 
-        commissioner = Commissioner.new(cops)
+        commissioner = Commissioner.new(cops, forces)
         offenses = commissioner.investigate(processed_source)
         process_commissioner_errors(
           processed_source.file_path, commissioner.errors)
@@ -50,6 +50,14 @@ def cops
         end
       end
 
+      def forces
+        @forces ||= Force.all.each_with_object([]) do |force_class, forces|
+          joining_cops = cops.select { |cop| cop.join_force?(force_class) }
+          next if joining_cops.empty?
+          forces << force_class.new(joining_cops)
+        end
+      end
+
       private
 
       def cop_enabled?(cop_class)

lib/rubocop/cop/variable_inspector.rb → lib/rubocop/cop/variable_force.rb

@@ -2,10 +2,27 @@
 
 module Rubocop
   module Cop
-    # This module provides a way to track local variables and scopes of Ruby.
-    # This is intended to be used as mix-in, and the user class may override
-    # some of the hook methods.
-    module VariableInspector
+    # This force provides a way to track local variables and scopes of Ruby.
+    # Cops intertact with this force need to override some of the hook methods.
+    #
+    #     def before_entering_scope(scope, variable_table)
+    #     end
+    #
+    #     def after_entering_scope(scope, variable_table)
+    #     end
+    #
+    #     def before_leaving_scope(scope, variable_table)
+    #     end
+    #
+    #     def after_leaving_scope(scope, variable_table)
+    #     end
+    #
+    #     def before_declaring_variable(variable, variable_table)
+    #     end
+    #
+    #     def after_declaring_variable(variable, variable_table)
+    #     end
+    class VariableForce < Force # rubocop:disable ClassLength
       VARIABLE_ASSIGNMENT_TYPE = :lvasgn
       REGEXP_NAMED_CAPTURE_TYPE = :match_with_lvasgn
       VARIABLE_ASSIGNMENT_TYPES =
@@ -42,27 +59,26 @@ module VariableInspector
       TWISTED_SCOPE_TYPES = [:block, :class, :sclass, :defs].freeze
       SCOPE_TYPES = (TWISTED_SCOPE_TYPES + [:top_level, :module, :def]).freeze
 
+      def self.wrap_with_top_level_node(node)
+        # This is a custom node type, not defined in Parser.
+        Parser::AST::Node.new(:top_level, [node])
+      end
+
       def variable_table
         @variable_table ||= VariableTable.new(self)
       end
 
       # Starting point.
-      def inspect_variables(root_node)
+      def investigate(processed_source)
+        root_node = processed_source.ast
         return unless root_node
 
         # Wrap the root node with :top_level scope node.
-        top_level_node = wrap_with_top_level_node(root_node)
+        top_level_node = self.class.wrap_with_top_level_node(root_node)
 
         inspect_variables_in_scope(top_level_node)
       end
 
-      def wrap_with_top_level_node(node)
-        # This is a custom node type, not defined in Parser.
-        Parser::AST::Node.new(:top_level, [node])
-      end
-
-      module_function :wrap_with_top_level_node
-
       # This is called for each scope recursively.
       def inspect_variables_in_scope(scope_node)
         variable_table.push_scope(scope_node)
@@ -339,24 +355,19 @@ def scanned_nodes
         @scanned_nodes ||= []
       end
 
-      # Hooks
-
-      def before_entering_scope(scope)
-      end
-
-      def after_entering_scope(scope)
-      end
-
-      def before_leaving_scope(scope)
-      end
-
-      def after_leaving_scope(scope)
-      end
-
-      def before_declaring_variable(variable_variable)
-      end
-
-      def after_declaring_variable(variable_variable)
+      # Hooks invoked by VariableTable.
+      [
+        :before_entering_scope,
+        :after_entering_scope,
+        :before_leaving_scope,
+        :after_leaving_scope,
+        :before_declaring_variable,
+        :after_declaring_variable
+      ].each do |hook|
+        define_method(hook) do |arg|
+          # Invoke hook in cops.
+          run_hook(hook, arg, variable_table)
+        end
       end
 
       # Post condition loops

lib/rubocop/cop/variable_inspector/assignment.rb → lib/rubocop/cop/variable_force/assignment.rb

@@ -2,7 +2,7 @@
 
 module Rubocop
   module Cop
-    module VariableInspector
+    class VariableForce
       # This class represents each assignment of a variable.
       class Assignment
         include Locatable

lib/rubocop/cop/variable_inspector/locatable.rb → lib/rubocop/cop/variable_force/locatable.rb

@@ -2,7 +2,7 @@
 
 module Rubocop
   module Cop
-    module VariableInspector
+    class VariableForce
       # This module provides a way to locate the conditional branch the node is
       # in. This is intended to be used as mix-in.
       module Locatable

lib/rubocop/cop/variable_inspector/reference.rb → lib/rubocop/cop/variable_force/reference.rb

@@ -2,7 +2,7 @@
 
 module Rubocop
   module Cop
-    module VariableInspector
+    class VariableForce
       # This class represents each reference of a variable.
       class Reference
         include Locatable

lib/rubocop/cop/variable_inspector/scope.rb → lib/rubocop/cop/variable_force/scope.rb

@@ -2,7 +2,7 @@
 
 module Rubocop
   module Cop
-    module VariableInspector
+    class VariableForce
       # A Scope represents a context of local variable visibility.
       # This is a place where local variables belong to.
       # A scope instance holds a scope node and variable entries.

lib/rubocop/cop/variable_inspector/variable.rb → lib/rubocop/cop/variable_force/variable.rb

@@ -2,7 +2,7 @@
 
 module Rubocop
   module Cop
-    module VariableInspector
+    class VariableForce
       # A Variable represents existance of a local variable.
       # This holds a variable declaration node,
       # and some states of the variable.

lib/rubocop/cop/variable_inspector/variable_table.rb → lib/rubocop/cop/variable_force/variable_table.rb

@@ -2,7 +2,7 @@
 
 module Rubocop
   module Cop
-    module VariableInspector
+    class VariableForce
       # A VariableTable manages the lifetime of all scopes and local variables
       # in a program.
       # This holds scopes as stack structure, and provides a way to add local