4 files changed, 14 insertions, 25 deletions

diff --git a/lisp/allout.el b/lisp/allout.el
index a123ece9b95..242b1f2c87f 100644
--- a/lisp/allout.el
+++ b/lisp/allout.el
@@ -4351,7 +4351,7 @@ subtopics into siblings of the item."
             (let ((children-chart (allout-chart-subtree 1)))
               (if (listp (car children-chart))
                   ;; whoops:
-                  (setq children-chart (allout-flatten children-chart)))
+                  (setq children-chart (flatten-tree children-chart)))
               (save-excursion
                 (dolist (child-point children-chart)
                   (goto-char child-point)
@@ -6547,14 +6547,7 @@ If BEG is bigger than END we return 0."
   (apply 'concat
          (mapcar (lambda (char) (if (= char ?%) "%%" (char-to-string char)))
                  string)))
-;;;_  : lists
-;;;_   > allout-flatten (list)
-(defun allout-flatten (list)
-  "Return a list of all atoms in list."
-  ;; classic.
-  (cond ((null list) nil)
-        ((atom (car list)) (cons (car list) (allout-flatten (cdr list))))
-        (t (append (allout-flatten (car list)) (allout-flatten (cdr list))))))
+(define-obsolete-function-alias 'allout-flatten #'flatten-tree "27.1")
 ;;;_  : Compatibility:
 ;;;_   : xemacs undo-in-progress provision:
 (unless (boundp 'undo-in-progress)
diff --git a/lisp/org/org-protocol.el b/lisp/org/org-protocol.el
index 33957ee3269..bb88c2fe1fd 100644
--- a/lisp/org/org-protocol.el
+++ b/lisp/org/org-protocol.el
@@ -349,17 +349,20 @@ returned list."
           ret)
       l)))
 
-(defun org-protocol-flatten (list)
-  "Transform LIST into a flat list.
+(if (fboundp 'flatten-tree)
+    (defalias 'org-protocol-flatten 'flatten-tree)
+  (defun org-protocol-flatten (list)
+    "Transform LIST into a flat list.
 
 Greedy handlers might receive a list like this from emacsclient:
 \((\"/dir/org-protocol:/greedy:/~/path1\" (23 . 12)) (\"/dir/param\"))
 where \"/dir/\" is the absolute path to emacsclients working directory.
 This function transforms it into a flat list."
-  (if (null list) ()
-    (if (listp list)
-        (append (org-protocol-flatten (car list)) (org-protocol-flatten (cdr list)))
-      (list list))))
+    (if (null list) ()
+      (if (listp list)
+          (append (org-protocol-flatten (car list))
+                  (org-protocol-flatten (cdr list)))
+        (list list)))))
 
 (defun org-protocol-parse-parameters (info &optional new-style default-order)
   "Return a property list of parameters from INFO.
diff --git a/lisp/progmodes/hideif.el b/lisp/progmodes/hideif.el
index 62e8c453389..84cbb6e6d17 100644
--- a/lisp/progmodes/hideif.el
+++ b/lisp/progmodes/hideif.el
@@ -672,12 +672,7 @@ that form should be displayed.")
        result))
     (nreverse result)))
 
-(defun hif-flatten (l)
-  "Flatten a tree."
-  (apply #'nconc
-         (mapcar (lambda (x) (if (listp x)
-                                 (hif-flatten x)
-                               (list x))) l)))
+(define-obsolete-function-alias 'hif-flatten #'flatten-tree "27.1")
 
 (defun hif-expand-token-list (tokens &optional macroname expand_list)
   "Perform expansion on TOKENS till everything expanded.
@@ -748,7 +743,7 @@ detecting self-reference."
 
          expanded))
 
-      (hif-flatten (nreverse expanded)))))
+      (flatten-tree (nreverse expanded)))))
 
 (defun hif-parse-exp (token-list &optional macroname)
   "Parse the TOKEN-LIST.
@@ -1166,7 +1161,7 @@ preprocessing token"
         (setq actual-parms (cdr actual-parms)))
 
       ;; Replacement completed, flatten the whole token list
-      (setq macro-body (hif-flatten macro-body))
+      (setq macro-body (flatten-tree macro-body))
 
       ;; Stringification and token concatenation happens here
       (hif-token-concatenation (hif-token-stringification macro-body)))))
diff --git a/lisp/progmodes/js.el b/lisp/progmodes/js.el
index ddba7636b4a..11ccb5fc527 100644
--- a/lisp/progmodes/js.el
+++ b/lisp/progmodes/js.el
@@ -623,8 +623,6 @@ then the \".\"s will be lined up:
   "Parse state at `js--last-parse-pos'.")
 (make-variable-buffer-local 'js--state-at-last-parse-pos)
 
-(define-obsolete-function-alias 'js--flatten-list #'flatten-tree "27.1")
-
 (defun js--maybe-join (prefix separator suffix &rest list)
   "Helper function for `js--update-quick-match-re'.
 If LIST contains any element that is not nil, return its non-nil