In Ruby 2.4, Set#=== is harmonized with Ruby 2.5+ to call include?

CHANGELOG.md

@@ -9,6 +9,10 @@
 * [#89](https://github.com/rubocop-hq/rubocop-ast/pull/89): Support right hand assignment for Ruby 2.8 (3.0) parser. ([@koic][])
 * [#93](https://github.com/rubocop-hq/rubocop-ast/pull/93): Add `Node#{left|right}_sibling{s}` ([@marcandre][])
 
+### Changes
+
+* [#x](https://github.com/rubocop-hq/rubocop-ast/issue/x): In Ruby 2.4, `Set#===` is harmonized with Ruby 2.5+ to call `include?`. ([@marcandre][])
+
 ## 0.3.0 (2020-08-01)
 
 ### New features

lib/rubocop/ast.rb

@@ -5,6 +5,7 @@
 require 'set'
 
 require_relative 'ast/ext/range'
+require_relative 'ast/ext/set'
 require_relative 'ast/node_pattern'
 require_relative 'ast/sexp'
 require_relative 'ast/node'

lib/rubocop/ast/ext/set.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+# Harmonize `Set#===`
+unless Set[:foo] === :foo # typically RUBY_VERSION <= 2.4
+  class Set
+    alias === include?
+  end
+end