merge revision(s) 8c360ce713f57d4177de833297364f6f6d950420: [Backport #19589]

	hash.c: Fix hash_iter_lev_dec corrupting shape

	[Bug #19589]

	When decrementing `iter_lev` from `65` to `64` the flags would be
	corrupted, causing the shape_id to be invalid.
	---
	 hash.c                 | 12 +++++++++---
	 test/ruby/test_hash.rb | 11 +++++++++++
	 2 files changed, 20 insertions(+), 3 deletions(-)

1 files changed, 11 insertions, 0 deletions

diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index 83d16d462e..8b6065146c 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -1556,6 +1556,17 @@ class TestHash < Test::Unit::TestCase
     end
   end
 
+  def hash_iter_recursion(h, level)
+    return if level == 0
+    h.each_key {}
+    h.each_value { hash_iter_recursion(h, level - 1) }
+  end
+
+  def test_iterlevel_in_ivar_bug19589
+    h = { a: nil }
+    hash_iter_recursion(h, 200)
+  end
+
   def test_threaded_iter_level
     bug9105 = '[ruby-dev:47807] [Bug #9105]'
     h = @cls[1=>2]