Raise an exception when Hash#compare_by_identity during its iteration

2 files changed, 12 insertions, 0 deletions

diff --git a/hash.c b/hash.c
index 83b9e9ce66..78fbfb866c 100644
--- a/hash.c
+++ b/hash.c
@@ -4367,6 +4367,9 @@ rb_hash_compare_by_id(VALUE hash)
     if (rb_hash_compare_by_id_p(hash)) return hash;
 
     rb_hash_modify_check(hash);
+    if (hash_iterating_p(hash)) {
+        rb_raise(rb_eRuntimeError, "compare_by_identity during iteration");
+    }
     ar_force_convert_table(hash, __FILE__, __LINE__);
     HASH_ASSERT(RHASH_ST_TABLE_P(hash));
 
diff --git a/test/ruby/test_hash.rb b/test/ruby/test_hash.rb
index a01f730904..970d0938bf 100644
--- a/test/ruby/test_hash.rb
+++ b/test/ruby/test_hash.rb
@@ -2272,4 +2272,13 @@ class TestHashOnly < Test::Unit::TestCase
       end;
     end
   end
+
+  def test_compare_by_identity_during_iteration
+    h = { 1 => 1 }
+    h.each do
+      assert_raise(RuntimeError, "compare_by_identity during iteration") do
+        h.compare_by_identity
+      end
+    end
+  end
 end