Copy compare_by_identity flag for empty hashes in Hash.ruby2_keywords_hash

This was already copied for non-empty hashes.  As Hash.ruby2_keywords_hash
copies default values, it should also copy the compare_by_identity flag.

Partially Fixes [Bug #19113]

1 files changed, 6 insertions, 3 deletions

diff --git a/hash.c b/hash.c
index 40866509d1..285a13494a 100644
--- a/hash.c
+++ b/hash.c
@@ -1972,9 +1972,12 @@ static VALUE
 rb_hash_s_ruby2_keywords_hash(VALUE dummy, VALUE hash)
 {
     Check_Type(hash, T_HASH);
-    hash = rb_hash_dup(hash);
-    RHASH(hash)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
-    return hash;
+    VALUE tmp = rb_hash_dup(hash);
+    if (RHASH_EMPTY_P(hash) && rb_hash_compare_by_id_p(hash)) {
+        rb_hash_compare_by_id(tmp);
+    }
+    RHASH(tmp)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
+    return tmp;
 }
 
 struct rehash_arg {