* string.c (str_nth_len): count ascii-only run at the end. this

  bug appears only when single-byte-optimization is disabled due
  to unknown coderange.  [ruby-core:41896] [Bug #5836]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@34208 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

3 files changed, 16 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 81182f2cda..84e3283712 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Jan  4 14:24:33 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* string.c (str_nth_len): count ascii-only run at the end.  this
+	  bug appears only when single-byte-optimization is disabled due
+	  to unknown coderange.  [ruby-core:41896] [Bug #5836]
+
 Wed Jan  4 11:32:07 2012  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* win32/win32.c (check_valid_dir): special case for a root directory.
diff --git a/string.c b/string.c
index 61703a7057..606fef7a42 100644
--- a/string.c
+++ b/string.c
@@ -1483,6 +1483,7 @@ str_nth_len(const char *p, const char *e, long *nthp, rb_encoding *enc)
             if (ISASCII(*p)) {
                 p2 = search_nonascii(p, e2);
                 if (!p2) {
+		    nth -= e2 - p;
 		    *nthp = nth;
                     return (char *)e2;
                 }
diff --git a/test/ruby/test_m17n.rb b/test/ruby/test_m17n.rb
index f4d3dcbdad..cc42514da2 100644
--- a/test/ruby/test_m17n.rb
+++ b/test/ruby/test_m17n.rb
@@ -930,6 +930,15 @@ class TestM17N < Test::Unit::TestCase
     assert_equal("\u{439}", "a\u{439}bcdefghijklmnop"[1, 1][0, 1], bug2379)
   end
 
+  def test_str_aref_force_encoding
+    bug5836 = '[ruby-core:41896]'
+    Encoding.list.each do |enc|
+      next unless enc.ascii_compatible?
+      s = "abc".force_encoding(enc)
+      assert_equal("", s[3, 1], bug5836)
+    end
+  end
+
   def test_aset
     s = e("\xa3\xb0\xa3\xb1\xa3\xb2\xa3\xb3\xa3\xb4")
     assert_raise(Encoding::CompatibilityError){s["\xb0\xa3"] = "foo"}