sprintf_dynamic_hash.patch

diff --git a/hash.c b/hash.c
index 3cdc75e..ef2acd7 100644
--- a/hash.c
+++ b/hash.c
@@ -888,7 +888,7 @@ rb_hash_fetch(VALUE hash, VALUE key)
  *     h.default(2)                            #=> 20
  */
 
-static VALUE
+VALUE
 rb_hash_default(int argc, VALUE *argv, VALUE hash)
 {
     VALUE key, ifnone;
diff --git a/include/ruby/intern.h b/include/ruby/intern.h
index 56865f3..0be1aee 100644
--- a/include/ruby/intern.h
+++ b/include/ruby/intern.h
@@ -521,6 +521,7 @@ VALUE rb_hash_clear(VALUE);
 VALUE rb_hash_delete_if(VALUE);
 VALUE rb_hash_delete(VALUE,VALUE);
 VALUE rb_hash_set_ifnone(VALUE hash, VALUE ifnone);
+VALUE rb_hash_default(int argc, VALUE *argv, VALUE hash);
 typedef VALUE rb_hash_update_func(VALUE newkey, VALUE oldkey, VALUE value);
 VALUE rb_hash_update_by(VALUE hash1, VALUE hash2, rb_hash_update_func *func);
 struct st_table *rb_hash_tbl(VALUE);
diff --git a/sprintf.c b/sprintf.c
index 4549791..567cad4 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -610,7 +610,12 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 					   enc);
 		if (sym != Qnil) nextvalue = rb_hash_lookup2(hash, sym, Qundef);
 		if (nextvalue == Qundef) {
-		    rb_enc_raise(enc, rb_eKeyError, "key%.*s not found", len, start);
+            if (rb_hash_default(0, NULL, hash) != Qnil || FL_TEST(hash, HASH_PROC_DEFAULT)) {
+                nextvalue = rb_hash_aref(hash, sym);
+            }
+            else {
+                rb_enc_raise(enc, rb_eKeyError, "key%.*s not found", len, start);
+            }
 		}
 		if (term == '}') goto format_s;
 		p++;