share @@accept_charset

* lib/cgi/{core,util}.rb: include CGI::Util not only extending, to
  share `@@accept_charset` class variable, so that it is always
  accessible.  [ruby-core:80986] [Bug #13539]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58576 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/cgi/core.rb

@@ -4,6 +4,13 @@
 # generating HTTP responses.
 #++
 class CGI
+  unless const_defined?(:Util)
+    module Util
+      @@accept_charset = "UTF-8" # :nodoc:
+    end
+    include Util
+    extend Util
+  end
 
   $CGI_ENV = ENV    # for FCGI support
 
@@ -734,7 +741,7 @@ class CGI
   #
   #   CGI.accept_charset = "EUC-JP"
   #
-  @@accept_charset="UTF-8"
+  @@accept_charset="UTF-8" if false # needed for rdoc?
 
   # Return the accept character set for all new CGI instances.
   def self.accept_charset

lib/cgi/util.rb

@@ -1,5 +1,9 @@
 # frozen_string_literal: true
-class CGI; module Util; end; extend Util; end
+class CGI
+  module Util; end
+  include Util
+  extend Util
+end
 module CGI::Util
   @@accept_charset="UTF-8" unless defined?(@@accept_charset)
   # URL-encode a string.

test/cgi/test_cgi_util.rb

@@ -60,6 +60,10 @@ class CGIUtilTest < Test::Unit::TestCase
     return unless defined?(::Encoding)
 
     assert_raise(TypeError) {CGI.unescape('', nil)}
+    assert_separately(%w[-rcgi/util], "#{<<-"begin;"}\n#{<<-"end;"}")
+    begin;
+      assert_equal("", CGI.unescape(''))
+    end;
   end
 
   def test_cgi_pretty