Get rid of indirect sharing

* string.c (str_duplicate): share the root shared string if the
  original string is already sharing, so that all shared strings
  refer the root shared string directly.  indirect sharing can
  cause a dangling pointer.

[Bug #15792]

1 files changed, 9 insertions, 0 deletions

diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index d94c4da7ae..f591f7ea9d 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -2961,6 +2961,15 @@ CODE
   end
 =end
 
+  def test_nesting_shared
+    a = ('a' * 24).encode(Encoding::ASCII).gsub('x', '')
+    hash = {}
+    hash[a] = true
+    assert_equal(('a' * 24), a)
+    4.times { GC.start }
+    assert_equal(('a' * 24), a, '[Bug #15792]')
+  end
+
   def test_shared_force_encoding
     s = "\u{3066}\u{3059}\u{3068}".gsub(//, '')
     h = {}