Ripper::Lexer::Elem#state is defined since Ruby 2.5

And the required ruby version is 2.5 or later.

Author: nobu

lib/irb/color.rb

@@ -77,7 +77,7 @@ module Color
 
     class << self
       def colorable?
-        $stdout.tty? && supported? && (/mswin|mingw/ =~ RUBY_PLATFORM || (ENV.key?('TERM') && ENV['TERM'] != 'dumb'))
+        $stdout.tty? && (/mswin|mingw/ =~ RUBY_PLATFORM || (ENV.key?('TERM') && ENV['TERM'] != 'dumb'))
       end
 
       def inspect_colorable?(obj, seen: {}.compare_by_identity)
@@ -161,11 +161,6 @@ def without_circular_ref(obj, seen:, &block)
         seen.delete(obj)
       end
 
-      def supported?
-        return @supported if defined?(@supported)
-        @supported = Ripper::Lexer::Elem.method_defined?(:state)
-      end
-
       def scan(code, allow_last_error:)
         pos = [1, 0]