[fixes rubocop#22] Introduce Tuple, a frozen Array/Set

lib/rubocop/ast.rb

@@ -3,6 +3,7 @@
 require 'parser'
 require 'forwardable'
 
+require_relative 'ast/tuple'
 require_relative 'ast/node_pattern'
 require_relative 'ast/sexp'
 require_relative 'ast/node'

lib/rubocop/ast/node.rb

@@ -23,37 +23,37 @@ class Node < Parser::AST::Node # rubocop:disable Metrics/ClassLength
       extend NodePattern::Macros
 
       # <=> 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 = Tuple %i[== === != <= >= > <]
+
+      TRUTHY_LITERALS = Tuple %i[str dstr xstr int float sym dsym array
+                                 hash regexp true irange erange complex
+                                 rational regopt]
+      FALSEY_LITERALS = Tuple %i[false nil]
+      LITERALS = Tuple(TRUTHY_LITERALS + FALSEY_LITERALS)
+      COMPOSITE_LITERALS = Tuple %i[dstr xstr dsym array hash irange
+                                    erange regexp]
+      BASIC_LITERALS = Tuple(LITERALS - COMPOSITE_LITERALS)
+      MUTABLE_LITERALS = Tuple %i[str dstr xstr array hash
+                                  regexp irange erange]
+      IMMUTABLE_LITERALS = Tuple(LITERALS - MUTABLE_LITERALS)
+
+      EQUALS_ASSIGNMENTS = Tuple %i[lvasgn ivasgn cvasgn gvasgn
+                                    casgn masgn]
+      SHORTHAND_ASSIGNMENTS = Tuple %i[op_asgn or_asgn and_asgn]
+      ASSIGNMENTS = Tuple(EQUALS_ASSIGNMENTS + SHORTHAND_ASSIGNMENTS)
+
+      BASIC_CONDITIONALS = Tuple %i[if while until]
+      CONDITIONALS = Tuple[*BASIC_CONDITIONALS, :case]
+      VARIABLES = Tuple %i[ivar gvar cvar lvar]
+      REFERENCES = Tuple %i[nth_ref back_ref]
+      KEYWORDS = Tuple %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 = Tuple %i[and or]
+      SPECIAL_KEYWORDS = Tuple %w[__FILE__ __LINE__ __ENCODING__]
+      ARGUMENT_TYPES = Tuple %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 = Tuple %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
+        Tuple(Array.instance_methods - Object.instance_methods - [:to_a])
 
       def_delegators :to_a, *ARRAY_METHODS
     end

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

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

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

@@ -7,14 +7,14 @@ module AST
     #
     # @note this mixin expects `#method_name` and `#receiver` to be implemented
     module MethodIdentifierPredicates
-      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].freeze
+      ENUMERATOR_METHODS = Tuple %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]
 
       # http://phrogz.net/programmingruby/language.html#table_18.4
-      OPERATOR_METHODS = %i[| ^ & <=> == === =~ > >= < <= << >> + - * /
-                            % ** ~ +@ -@ !@ ~@ [] []= ! != !~ `].freeze
+      OPERATOR_METHODS = Tuple %i[| ^ & <=> == === =~ > >= < <= << >> + - * /
+                                  % ** ~ +@ -@ !@ ~@ [] []= ! != !~ `]
 
       # Checks whether the method name matches the argument.
       #

lib/rubocop/ast/traversal.rb

@@ -15,27 +15,27 @@ def walk(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 lambda redo retry
-                             forward_args forwarded_args
-                             match_var match_nil_pattern empty_else].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].freeze
-      SECOND_CHILD_ONLY = %i[lvasgn ivasgn cvasgn gvasgn optarg kwarg
-                             kwoptarg].freeze
+      NO_CHILD_NODES    = Tuple %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 lambda redo retry
+                                   forward_args forwarded_args
+                                   match_var match_nil_pattern empty_else]
+      ONE_CHILD_NODE    = Tuple %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  = Tuple %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]
+      SECOND_CHILD_ONLY = Tuple %i[lvasgn ivasgn cvasgn gvasgn optarg kwarg
+                                   kwoptarg]
 
       NO_CHILD_NODES.each do |type|
         module_eval("def on_#{type}(node); end", __FILE__, __LINE__)

lib/rubocop/ast/tuple.rb

@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module AST
+    # A frozen Array/Set
+    #
+    class Tuple < ::Array
+      extend Forwardable
+      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
+
+      def to_a
+        self
+      end
+
+      def_delegators :@to_set, :include?, :===
+    end
+  end
+end
+
+def Tuple(list) # rubocop:disable Naming/MethodName
+  RuboCop::AST::Tuple.new(list)
+end

spec/rubocop/ast/tuple_spec.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::AST::Tuple do
+  shared_examples 'a tuple' do
+    it { is_expected.to be_frozen }
+    it { expect(tuple.include?(:included)).to be true }
+    it { expect(tuple.include?(:not_included)).to be false }
+    it { is_expected.to eq tuple.dup }
+
+    describe '#to_a' do
+      subject { tuple.to_a }
+
+      it { is_expected.to equal tuple.to_a }
+      it { is_expected.to be_frozen }
+      it { is_expected.to include :included }
+    end
+
+    describe '#to_set' do
+      subject { tuple.to_set }
+
+      it { is_expected.to equal tuple.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(:tuple) { described_class.new(values) }
+
+    it_behaves_like 'a tuple'
+
+    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
+  end
+
+  describe '.[]' do
+    subject(:tuple) { described_class[*values] }
+
+    it_behaves_like 'a tuple'
+  end
+
+  describe '()' do
+    subject(:tuple) { Tuple values }
+
+    it_behaves_like 'a tuple'
+  end
+end