Fix circular list handling in seq-mapn

* lisp/emacs-lisp/seq.el (seq-mapn): Do not copy list arguments.
* test/lisp/emacs-lisp/seq-tests.el (test-seq-mapn-circular-lists):
  Add a regression test.

1 files changed, 5 insertions, 0 deletions

diff --git a/test/lisp/emacs-lisp/seq-tests.el b/test/lisp/emacs-lisp/seq-tests.el
index 2e533acce17..fc65c9834d6 100644
--- a/test/lisp/emacs-lisp/seq-tests.el
+++ b/test/lisp/emacs-lisp/seq-tests.el
@@ -386,5 +386,10 @@ Evaluate BODY for each created sequence.
   (should-error (seq-random-elt []))
   (should-error (seq-random-elt "")))
 
+(ert-deftest test-seq-mapn-circular-lists ()
+  (let ((l1 '#1=(1 . #1#)))
+    (should (equal (seq-mapn #'+ '(3 4 5 7) l1)
+                   '(4 5 6 8)))))
+
 (provide 'seq-tests)
 ;;; seq-tests.el ends here