Fix cl-concatenate (Bug#40180)

* lisp/emacs-lisp/cl-extra.el (cl-concatenate): Use apply, to avoid
adding extra nesting of args.
* test/lisp/emacs-lisp/cl-extra-tests.el (cl-concatenate): New test.

Author: npostavs

lisp/emacs-lisp/cl-extra.el

@@ -556,7 +556,7 @@ too large if positive or too small if negative)."
 (defun cl-concatenate (type &rest sequences)
   "Concatenate, into a sequence of type TYPE, the argument SEQUENCEs.
 \n(fn TYPE SEQUENCE...)"
-  (seq-concatenate type sequences))
+  (apply #'seq-concatenate type sequences))
 
 ;;; List functions.
 

test/lisp/emacs-lisp/cl-extra-tests.el

@@ -99,4 +99,12 @@
     ;; Test for Bug#33731.
     (should-not (eq s (cl-make-random-state s)))))
 
+(ert-deftest cl-concatenate ()
+  (should (equal (cl-concatenate 'list '(1 2 3) '(4 5 6))
+                 '(1 2 3 4 5 6)))
+  (should (equal (cl-concatenate 'vector [1 2 3] [4 5 6])
+                 [1 2 3 4 5 6]))
+  (should (equal (cl-concatenate 'string "123" "456")
+                 "123456")))
+
 ;;; cl-extra-tests.el ends here