[fixes rubocop#22] Introduce FastArray, a frozen Array with fast include?

Author: marcandre

.rubocop_todo.yml

@@ -32,7 +32,7 @@ Metrics/MethodLength:
 # Offense count: 1
 # Configuration parameters: CountComments.
 Metrics/ModuleLength:
-  Max: 101
+  Max: 102
 
 # Offense count: 1
 # Configuration parameters: ExpectMatchingDefinition, Regex, IgnoreExecutableScripts, AllowedAcronyms.

lib/rubocop/ast.rb

@@ -4,6 +4,7 @@
 require 'forwardable'
 require 'set'
 
+require_relative 'ast/fast_array'
 require_relative 'ast/node_pattern'
 require_relative 'ast/sexp'
 require_relative 'ast/node'

lib/rubocop/ast/fast_array.rb

@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module AST
+    # FastArray represents a frozen `Array` with fast lookup
+    # using `include?`.
+    # Like `Set`, the case equality `===` is an alias for `include?`
+    #
+    #     FOO = FastArray[:hello, :world]
+    #     FOO.include?(:hello) # => true, quickly
+    #
+    #     case bar
+    #     when FOO # Note: no splat
+    #       # decided quickly
+    #     # ...
+    class FastArray < ::Array
+      # Defines a function `FastArray(list)` similar to `Array(list)`
+      module Tool
+        def FastArray(list) # rubocop:disable Naming/MethodName
+          RuboCop::AST::FastArray.new(list)
+        end
+      end
+
+      attr_reader :to_set
+
+      def initialize(ary)
+        raise ArgumentError, 'Must be initialized with an array' unless ary.is_a?(Array)
+
+        super
+        freeze
+      end
+
+      def self.[](*values)
+        new(values)
+      end
+
+      def freeze
+        @to_set ||= Set.new(self).freeze
+        super
+      end
+
+      # Return self, not a newly allocated FastArray
+      def to_a
+        self
+      end
+
+      def include?(value)
+        @to_set.include?(value)
+      end
+
+      alias === include?
+    end
+  end
+end

lib/rubocop/ast/node.rb

@@ -21,39 +21,40 @@ module AST
     class Node < Parser::AST::Node # rubocop:disable Metrics/ClassLength
       include RuboCop::AST::Sexp
       extend NodePattern::Macros
+      extend FastArray::Tool
 
       # <=> isn't included here, because it doesn't return a boolean.
-      COMPARISON_OPERATORS = %i[== === != <= >= > <].freeze
-
-      TRUTHY_LITERALS = %i[str dstr xstr int float sym dsym array
-                           hash regexp true irange erange complex
-                           rational regopt].freeze
-      FALSEY_LITERALS = %i[false nil].freeze
-      LITERALS = (TRUTHY_LITERALS + FALSEY_LITERALS).freeze
-      COMPOSITE_LITERALS = %i[dstr xstr dsym array hash irange
-                              erange regexp].freeze
-      BASIC_LITERALS = (LITERALS - COMPOSITE_LITERALS).freeze
-      MUTABLE_LITERALS = %i[str dstr xstr array hash
-                            regexp irange erange].freeze
-      IMMUTABLE_LITERALS = (LITERALS - MUTABLE_LITERALS).freeze
-
-      EQUALS_ASSIGNMENTS = %i[lvasgn ivasgn cvasgn gvasgn
-                              casgn masgn].freeze
-      SHORTHAND_ASSIGNMENTS = %i[op_asgn or_asgn and_asgn].freeze
-      ASSIGNMENTS = (EQUALS_ASSIGNMENTS + SHORTHAND_ASSIGNMENTS).freeze
-
-      BASIC_CONDITIONALS = %i[if while until].freeze
-      CONDITIONALS = [*BASIC_CONDITIONALS, :case].freeze
-      VARIABLES = %i[ivar gvar cvar lvar].freeze
-      REFERENCES = %i[nth_ref back_ref].freeze
-      KEYWORDS = %i[alias and break case class def defs defined?
-                    kwbegin do else ensure for if module next
-                    not or postexe redo rescue retry return self
-                    super zsuper then undef until when while
-                    yield].freeze
-      OPERATOR_KEYWORDS = %i[and or].freeze
-      SPECIAL_KEYWORDS = %w[__FILE__ __LINE__ __ENCODING__].freeze
-      ARGUMENT_TYPES = %i[arg optarg restarg kwarg kwoptarg kwrestarg blockarg].freeze
+      COMPARISON_OPERATORS = FastArray %i[== === != <= >= > <]
+
+      TRUTHY_LITERALS = FastArray %i[str dstr xstr int float sym dsym array
+                                     hash regexp true irange erange complex
+                                     rational regopt]
+      FALSEY_LITERALS = FastArray %i[false nil]
+      LITERALS = FastArray(TRUTHY_LITERALS + FALSEY_LITERALS)
+      COMPOSITE_LITERALS = FastArray %i[dstr xstr dsym array hash irange
+                                        erange regexp]
+      BASIC_LITERALS = FastArray(LITERALS - COMPOSITE_LITERALS)
+      MUTABLE_LITERALS = FastArray %i[str dstr xstr array hash
+                                      regexp irange erange]
+      IMMUTABLE_LITERALS = FastArray(LITERALS - MUTABLE_LITERALS)
+
+      EQUALS_ASSIGNMENTS = FastArray %i[lvasgn ivasgn cvasgn gvasgn
+                                        casgn masgn]
+      SHORTHAND_ASSIGNMENTS = FastArray %i[op_asgn or_asgn and_asgn]
+      ASSIGNMENTS = FastArray(EQUALS_ASSIGNMENTS + SHORTHAND_ASSIGNMENTS)
+
+      BASIC_CONDITIONALS = FastArray %i[if while until]
+      CONDITIONALS = FastArray[*BASIC_CONDITIONALS, :case]
+      VARIABLES = FastArray %i[ivar gvar cvar lvar]
+      REFERENCES = FastArray %i[nth_ref back_ref]
+      KEYWORDS = FastArray %i[alias and break case class def defs defined?
+                              kwbegin do else ensure for if module next
+                              not or postexe redo rescue retry return self
+                              super zsuper then undef until when while
+                              yield]
+      OPERATOR_KEYWORDS = FastArray %i[and or]
+      SPECIAL_KEYWORDS = FastArray %w[__FILE__ __LINE__ __ENCODING__]
+      ARGUMENT_TYPES = FastArray %i[arg optarg restarg kwarg kwoptarg kwrestarg blockarg]
 
       # @see https://www.rubydoc.info/gems/ast/AST/Node:initialize
       def initialize(type, children = [], properties = {})

lib/rubocop/ast/node/block_node.rb

@@ -11,7 +11,7 @@ module AST
     class BlockNode < Node
       include MethodIdentifierPredicates
 
-      VOID_CONTEXT_METHODS = %i[each tap].freeze
+      VOID_CONTEXT_METHODS = FastArray %i[each tap]
 
       # The `send` node associated with this block.
       #

lib/rubocop/ast/node/mixin/collection_node.rb

@@ -7,7 +7,7 @@ module CollectionNode
       extend Forwardable
 
       ARRAY_METHODS =
-        (Array.instance_methods - Object.instance_methods - [:to_a]).freeze
+        Array.instance_methods - Object.instance_methods - [:to_a]
 
       def_delegators :to_a, *ARRAY_METHODS
     end

lib/rubocop/ast/node/mixin/method_dispatch_node.rb

@@ -8,9 +8,10 @@ module AST
     module MethodDispatchNode
       extend NodePattern::Macros
       include MethodIdentifierPredicates
+      extend FastArray::Tool
 
-      ARITHMETIC_OPERATORS = %i[+ - * / % **].freeze
-      SPECIAL_MODIFIERS = %w[private protected].freeze
+      ARITHMETIC_OPERATORS = FastArray %i[+ - * / % **]
+      SPECIAL_MODIFIERS = FastArray %w[private protected]
 
       # The receiving node of the method dispatch.
       #

lib/rubocop/ast/node/mixin/method_identifier_predicates.rb

@@ -7,23 +7,25 @@ module AST
     #
     # @note this mixin expects `#method_name` and `#receiver` to be implemented
     module MethodIdentifierPredicates # rubocop:disable Metrics/ModuleLength
-      ENUMERATOR_METHODS = %i[collect collect_concat detect downto each
-                              find find_all find_index inject loop map!
-                              map reduce reject reject! reverse_each select
-                              select! times upto].to_set.freeze
+      extend FastArray::Tool
 
-      ENUMERABLE_METHODS = (Enumerable.instance_methods + [:each]).to_set.freeze
+      ENUMERATOR_METHODS = FastArray %i[collect collect_concat detect downto each
+                                        find find_all find_index inject loop map!
+                                        map reduce reject reject! reverse_each select
+                                        select! times upto]
+
+      ENUMERABLE_METHODS = FastArray(Enumerable.instance_methods + [:each])
 
       # http://phrogz.net/programmingruby/language.html#table_18.4
-      OPERATOR_METHODS = %i[| ^ & <=> == === =~ > >= < <= << >> + - * /
-                            % ** ~ +@ -@ !@ ~@ [] []= ! != !~ `].to_set.freeze
+      OPERATOR_METHODS = FastArray %i[| ^ & <=> == === =~ > >= < <= << >> + - * /
+                                      % ** ~ +@ -@ !@ ~@ [] []= ! != !~ `]
 
-      NONMUTATING_BINARY_OPERATOR_METHODS = %i[* / % + - == === != < > <= >= <=>].to_set.freeze
-      NONMUTATING_UNARY_OPERATOR_METHODS = %i[+@ -@ ~ !].to_set.freeze
-      NONMUTATING_OPERATOR_METHODS = (NONMUTATING_BINARY_OPERATOR_METHODS +
-        NONMUTATING_UNARY_OPERATOR_METHODS).freeze
+      NONMUTATING_BINARY_OPERATOR_METHODS = FastArray %i[* / % + - == === != < > <= >= <=>]
+      NONMUTATING_UNARY_OPERATOR_METHODS = FastArray %i[+@ -@ ~ !]
+      NONMUTATING_OPERATOR_METHODS = FastArray(NONMUTATING_BINARY_OPERATOR_METHODS +
+        NONMUTATING_UNARY_OPERATOR_METHODS)
 
-      NONMUTATING_ARRAY_METHODS = %i[
+      NONMUTATING_ARRAY_METHODS = FastArray %i[
         all? any? assoc at bsearch bsearch_index collect
         combination compact count cycle deconstruct difference
         dig drop drop_while each each_index empty? eql?
@@ -36,19 +38,19 @@ module MethodIdentifierPredicates # rubocop:disable Metrics/ModuleLength
         size slice sort sum take take_while
         to_a to_ary to_h to_s transpose union uniq
         values_at zip |
-      ].to_set.freeze
+      ]
 
-      NONMUTATING_HASH_METHODS = %i[
+      NONMUTATING_HASH_METHODS = FastArray %i[
         any? assoc compact dig each each_key each_pair
         each_value empty? eql? fetch fetch_values filter
         flatten has_key? has_value? hash include? inspect
         invert key key? keys? length member? merge rassoc
         rehash reject select size slice to_a to_h to_hash
         to_proc to_s transform_keys transform_values value?
         values values_at
-      ].to_set.freeze
+      ]
 
-      NONMUTATING_STRING_METHODS = %i[
+      NONMUTATING_STRING_METHODS = FastArray %i[
         ascii_only? b bytes bytesize byteslice capitalize
         casecmp casecmp? center chars chomp chop chr codepoints
         count crypt delete delete_prefix delete_suffix
@@ -61,7 +63,7 @@ module MethodIdentifierPredicates # rubocop:disable Metrics/ModuleLength
         strip sub succ sum swapcase to_a to_c to_f to_i to_r to_s
         to_str to_sym tr tr_s unicode_normalize unicode_normalized?
         unpack unpack1 upcase upto valid_encoding?
-      ].to_set.freeze
+      ]
 
       # Checks whether the method name matches the argument.
       #

lib/rubocop/ast/traversal.rb

@@ -8,36 +8,38 @@ module AST
     # Override methods to perform custom processing. Remember to call `super`
     # if you want to recursively process descendant nodes.
     module Traversal
+      extend FastArray::Tool
+
       def walk(node)
         return if node.nil?
 
         send(:"on_#{node.type}", node)
         nil
       end
 
-      NO_CHILD_NODES    = %i[true false nil int float complex
-                             rational str sym regopt self lvar
-                             ivar cvar gvar nth_ref back_ref cbase
-                             arg restarg blockarg shadowarg
-                             kwrestarg zsuper redo retry
-                             forward_args forwarded_args
-                             match_var match_nil_pattern empty_else
-                             forward_arg lambda procarg0 __ENCODING__].freeze
-      ONE_CHILD_NODE    = %i[splat kwsplat block_pass not break next
-                             preexe postexe match_current_line defined?
-                             arg_expr pin match_rest if_guard unless_guard
-                             match_with_trailing_comma].freeze
-      MANY_CHILD_NODES  = %i[dstr dsym xstr regexp array hash pair
-                             mlhs masgn or_asgn and_asgn
-                             undef alias args super yield or and
-                             while_post until_post iflipflop eflipflop
-                             match_with_lvasgn begin kwbegin return
-                             in_match match_alt
-                             match_as array_pattern array_pattern_with_tail
-                             hash_pattern const_pattern
-                             index indexasgn].freeze
-      SECOND_CHILD_ONLY = %i[lvasgn ivasgn cvasgn gvasgn optarg kwarg
-                             kwoptarg].freeze
+      NO_CHILD_NODES    = FastArray %i[true false nil int float complex
+                                       rational str sym regopt self lvar
+                                       ivar cvar gvar nth_ref back_ref cbase
+                                       arg restarg blockarg shadowarg
+                                       kwrestarg zsuper redo retry
+                                       forward_args forwarded_args
+                                       match_var match_nil_pattern empty_else
+                                       forward_arg lambda procarg0 __ENCODING__]
+      ONE_CHILD_NODE    = FastArray %i[splat kwsplat block_pass not break next
+                                       preexe postexe match_current_line defined?
+                                       arg_expr pin match_rest if_guard unless_guard
+                                       match_with_trailing_comma]
+      MANY_CHILD_NODES  = FastArray %i[dstr dsym xstr regexp array hash pair
+                                       mlhs masgn or_asgn and_asgn
+                                       undef alias args super yield or and
+                                       while_post until_post iflipflop eflipflop
+                                       match_with_lvasgn begin kwbegin return
+                                       in_match match_alt
+                                       match_as array_pattern array_pattern_with_tail
+                                       hash_pattern const_pattern
+                                       index indexasgn]
+      SECOND_CHILD_ONLY = FastArray %i[lvasgn ivasgn cvasgn gvasgn optarg kwarg
+                                       kwoptarg]
 
       NO_CHILD_NODES.each do |type|
         module_eval("def on_#{type}(node); end", __FILE__, __LINE__)

spec/rubocop/ast/fast_array_spec.rb

@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::AST::FastArray do
+  shared_examples 'a fast_array' do
+    it { is_expected.to be_frozen }
+    it { expect(fast_array.include?(:included)).to be true }
+    it { expect(fast_array.include?(:not_included)).to be false }
+    it { is_expected.to eq fast_array.dup }
+
+    describe '#to_a' do
+      subject { fast_array.to_a }
+
+      it { is_expected.to equal fast_array.to_a }
+      it { is_expected.to be_frozen }
+      it { is_expected.to include :included }
+    end
+
+    describe '#to_set' do
+      subject { fast_array.to_set }
+
+      it { is_expected.to equal fast_array.to_set }
+      it { is_expected.to be_frozen }
+      it { is_expected.to be >= Set[:included] }
+    end
+  end
+
+  let(:values) { %i[included also_included] }
+
+  describe '.new' do
+    subject(:fast_array) { described_class.new(values) }
+
+    it_behaves_like 'a fast_array'
+
+    it 'enforces a single array argument' do
+      expect { described_class.new }.to raise_error ArgumentError
+      expect { described_class.new(5) }.to raise_error ArgumentError
+    end
+
+    it 'has freeze return self' do
+      expect(fast_array.freeze).to equal fast_array
+    end
+
+    it 'has the right case equality' do
+      expect(fast_array).to be === :included # rubocop:disable Style/CaseEquality
+    end
+  end
+
+  describe '.[]' do
+    subject(:fast_array) { described_class[*values] }
+
+    it_behaves_like 'a fast_array'
+  end
+
+  describe '()' do
+    subject(:fast_array) { FastArray values }
+
+    before { extend RuboCop::AST::FastArray::Tool }
+
+    it_behaves_like 'a fast_array'
+  end
+end