remove RHash::iter_lev.

iter_lev is used to detect the hash is iterating or not.
Usually, iter_lev should be very small number (1 or 2) so
`int` is overkill.

This patch introduce iter_lev in flags (7 bits, FL13 to FL19)
and if iter_lev exceeds this range, save it in hidden attribute.
We can get 1 word in RHash.

We can't modify frozen objects. Therefore I added new internal API
`rb_ivar_set_internal()` which allows us to set an attribute
even if the target object is frozen
if the name is hidden ivar (the name without `@` prefix).

1 files changed, 25 insertions, 0 deletions

diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index 243cad8d43..d973b1f763 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -1720,6 +1720,31 @@ class TestHash < Test::Unit::TestCase
     assert_equal(keys, h.keys.map(&:hash), msg)
   end
 
+  def hrec h, n, &b
+    if n > 0
+      h.each{hrec(h, n-1, &b)}
+    else
+      yield
+    end
+  end
+
+  def test_huge_iter_level
+    h = @cls[a: 1]
+    assert_raise(RuntimeError){
+      hrec(h, 1000){ h[:c] = 3 }
+    }
+
+    h = @cls[a: 1]
+    hrec(h, 1000){}
+    h[:c] = 3
+    assert_equal(3, h[:c])
+
+    h = @cls[a: 1]
+    h.freeze # set hidden attribute for a frozen object
+    hrec(h, 1000){}
+    assert_equal(1, h.size)
+  end
+
   class TestSubHash < TestHash
     class SubHash < Hash
       def reject(*)