Make seq-into return the sequence when no conversion needed

* lisp/emacs-lisp/seq.el (seq-into): Do not convert the sequence when
  no conversion is needed.
* test/lisp/emacs-lisp/seq-tests.el (test-seq-into-and-identity): Add
  a regression test checking for identity.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/lisp/emacs-lisp/seq-tests.el b/test/lisp/emacs-lisp/seq-tests.el
index fc65c9834d6..a7a43471de3 100644
--- a/test/lisp/emacs-lisp/seq-tests.el
+++ b/test/lisp/emacs-lisp/seq-tests.el
@@ -391,5 +391,13 @@ Evaluate BODY for each created sequence.
     (should (equal (seq-mapn #'+ '(3 4 5 7) l1)
                    '(4 5 6 8)))))
 
+(ert-deftest test-seq-into-and-identity ()
+  (let ((lst '(1 2 3))
+        (vec [1 2 3])
+        (str "foo bar"))
+    (should (eq (seq-into lst 'list) lst))
+    (should (eq (seq-into vec 'vector) vec))
+    (should (eq (seq-into str 'string) str))))
+
 (provide 'seq-tests)
 ;;; seq-tests.el ends here