New function flatten-tree

Co-authored-by: Basil L. Contovounesios <contovob@tcd.ie>

* doc/lispref/lists.texi: Document `flatten-tree'.

* lisp/progmodes/js.el (js--maybe-join):
* lisp/printing.el (pr-switches):
* lisp/lpr.el (lpr-print-region):
* lisp/gnus/nnimap.el (nnimap-find-wanted-parts):
* lisp/gnus/message.el (message-talkative-question):
* lisp/gnus/gnus-sum.el (gnus-remove-thread)
(gnus-thread-highest-number, gnus-thread-latest-date):
* lisp/eshell/esh-util.el (eshell-flatten-and-stringify):
* lisp/eshell/esh-opt.el (eshell-eval-using-options):
* lisp/eshell/esh-ext.el (eshell-external-command):
* lisp/eshell/em-xtra.el (eshell/expr):
* lisp/eshell/em-unix.el (eshell/rm, eshell-mvcpln-template)
(eshell/cat, eshell/make, eshell-poor-mans-grep, eshell-grep)
(eshell/du, eshell/time, eshell/diff, eshell/locate):
* lisp/eshell/em-tramp.el (eshell/su, eshell/sudo):
* lisp/eshell/em-term.el (eshell-exec-visual):
* lisp/eshell/em-dirs.el (eshell-dirs-substitute-cd, eshell/cd):
* lisp/eshell/em-basic.el (eshell/printnl):
Use new flatten-tree.

* lisp/progmodes/js.el (js--flatten-list):
* lisp/lpr.el (lpr-flatten-list):
* lisp/gnus/message.el (message-flatten-list):
* lisp/eshell/esh-util.el (eshell-flatten-list):
Obsolete in favor of Emacs-wide `flatten-tree'.

* lisp/subr.el (flatten-list): Alias to `flatten-tree' for
discoverability.

* lisp/subr.el (flatten-tree): New defun.

* test/lisp/subr-tests.el (subr-tests-flatten-tree): New test.

1 files changed, 2 insertions, 10 deletions

diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index fdaa4e82727..03f80616d9e 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -8051,7 +8051,7 @@ regular text mode tabbing command."
 If SHOW is non-nil, the arguments TEXT... are displayed in a temp buffer.
 The following arguments may contain lists of values."
   (if (and show
-	   (setq text (message-flatten-list text)))
+	   (setq text (flatten-tree text)))
       (save-window-excursion
         (with-output-to-temp-buffer " *MESSAGE information message*"
           (with-current-buffer " *MESSAGE information message*"
@@ -8061,15 +8061,7 @@ The following arguments may contain lists of values."
 	(funcall ask question))
     (funcall ask question)))
 
-(defun message-flatten-list (list)
-  "Return a new, flat list that contains all elements of LIST.
-
-\(message-flatten-list \\='(1 (2 3 (4 5 (6))) 7))
-=> (1 2 3 4 5 6 7)"
-  (cond ((consp list)
-	 (apply 'append (mapcar 'message-flatten-list list)))
-	(list
-	 (list list))))
+(define-obsolete-function-alias 'message-flatten-list #'flatten-tree "27.1")
 
 (defun message-generate-new-buffer-clone-locals (name &optional varstr)
   "Create and return a buffer with name based on NAME using `generate-new-buffer'.