Merge from origin/emacs-27

0a3682a566 * src/timefns.c: Add comments.
b16ba4041d ; lisp/emacs-lisp/seq.el: Explain why we don't use cl-lib ...
3cbf4cb796 Eliminate use of cl-concatenate in 'seq' package
363d927086 Fix bug with JIT stealth timers
818333c85a * doc/lispref/os.texi (time-subtract): Doc fix.

1 files changed, 9 insertions, 1 deletions

diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
index 0b946dd7365..e3037a71901 100644
--- a/lisp/emacs-lisp/seq.el
+++ b/lisp/emacs-lisp/seq.el
@@ -58,6 +58,10 @@
 
 (eval-when-compile (require 'cl-generic))
 
+;; We used to use some sequence functions from cl-lib, but this
+;; dependency was swapped around so that it will be easier to make
+;; seq.el preloaded in the future.  See also Bug#39761#26.
+
 (defmacro seq-doseq (spec &rest body)
   "Loop over a sequence.
 Evaluate BODY with VAR bound to each element of SEQUENCE, in turn.
@@ -285,7 +289,11 @@ sorted.  FUNCTION must be a function of one argument."
 TYPE must be one of following symbols: vector, string or list.
 
 \n(fn TYPE SEQUENCE...)"
-  (apply #'cl-concatenate type (seq-map #'seq-into-sequence sequences)))
+  (pcase type
+    ('vector (apply #'vconcat sequences))
+    ('string (apply #'concat sequences))
+    ('list (apply #'append (append sequences '(nil))))
+    (_ (error "Not a sequence type name: %S" type))))
 
 (cl-defgeneric seq-into-sequence (sequence)
   "Convert SEQUENCE into a sequence.