[ruby/optparse] The encoding argument of `Regexp.new` has been ignored since 1.9

https://github.com/ruby/optparse/commit/766f567405

lib/optparse.rb

@@ -2084,10 +2084,23 @@ XXX
       f |= Regexp::IGNORECASE if /i/ =~ o
       f |= Regexp::MULTILINE if /m/ =~ o
       f |= Regexp::EXTENDED if /x/ =~ o
-      k = o.delete("imx")
-      k = nil if k.empty?
+      case o = o.delete("imx")
+      when ""
+      when "u"
+        s = s.encode(Encoding::UTF_8)
+      when "e"
+        s = s.encode(Encoding::EUC_JP)
+      when "s"
+        s = s.encode(Encoding::SJIS)
+      when "n"
+        f |= Regexp::NOENCODING
+      else
+        raise OptionParser::InvalidArgument, "unknown regexp option - #{o}"
+      end
+    else
+      s ||= all
     end
-    Regexp.new(s || all, f, k)
+    Regexp.new(s, f)
   end
 
   #

test/optparse/test_optparse.rb

@@ -63,6 +63,9 @@ class TestOptionParser < Test::Unit::TestCase
     assert_equal(/foo/i, @reopt)
     assert_equal(%w"", no_error {@opt.parse!(%w"--regexp=/foo/n")})
     assert_equal(/foo/n, @reopt)
+    assert_equal(%w"", no_error {@opt.parse!(%W"--regexp=/\u{3042}/s")})
+    assert_equal(Encoding::Windows_31J, @reopt.encoding)
+    assert_equal("\x82\xa0".force_encoding(Encoding::Windows_31J), @reopt.source)
   end
 
   def test_into