From e85b19dba86bc3a5937376a0001453dbe3a5dc24 Mon Sep 17 00:00:00 2001
From: Max Nikulin <manikulin@gmail.com>
Date: Wed, 5 Jul 2023 22:50:44 +0700
Subject: [PATCH v2 2/2] org-compat.el: `org--flatten-tree' for Emacs-26
 compatibility

* lisp/org-compat.el (org--flatten-tree): New internal compatibility
alias or function based on `flatten-tree' added to Emacs-27.1.
* lisp/org-protocol.el (org-protocol-flatten): Convert to an obsolete
function alias.
(org-protocol-flatten-greedy): Use the `org--flatten-tree' new
compatibility alias or function instead of `org-protocol-flatten'.
* lisp/org-src.el (org-src--get-known-shells): Make the function
compatible with Emacs-26 by using `org--flatten-tree' instead of
`flatten-tree'.

Reported as: Justin to emacs-orgmode. [PATCH] org-src: flatten-tree is
Emacs 27.1; require compat. Tue, 4 Jul 2023 19:21:05 -0400.
https://list.orgmode.org/0288575b-fde8-0e7d-ac74-1f0ac93ce56f@vallon.homeip.net
---
 lisp/org-compat.el   | 19 +++++++++++++++++++
 lisp/org-protocol.el | 24 +++++++++---------------
 lisp/org-src.el      |  2 +-
 3 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/lisp/org-compat.el b/lisp/org-compat.el
index c5ab655d2..bbda04a15 100644
--- a/lisp/org-compat.el
+++ b/lisp/org-compat.el
@@ -211,6 +211,25 @@     (defmacro org-combine-change-calls (_beg _end &rest body)
       `(progn ,@body))
   (defalias 'org-combine-change-calls 'combine-change-calls))
 
+;; `flatten-tree' was added in Emacs 27.1.
+(if (fboundp 'flatten-tree)
+    (defalias 'org--flatten-tree #'flatten-tree)
+  ;; The implementation is taken from Emacs subr.el 8664ba18c7c5.
+  (defun org--flatten-tree (tree)
+    "Return a \"flattened\" copy of TREE.
+
+A `flatten-tree' polyfill for compatibility with Emacs versions
+older than 27.1"
+    (let (elems)
+      (while (consp tree)
+        (let ((elem (pop tree)))
+          (while (consp elem)
+            (push (cdr elem) tree)
+            (setq elem (car elem)))
+          (if elem (push elem elems))))
+      (if tree (push tree elems))
+      (nreverse elems))))
+
 (if (version< emacs-version "27.1")
     (defsubst org-replace-buffer-contents (source &optional _max-secs _max-costs)
       (replace-buffer-contents source))
diff --git a/lisp/org-protocol.el b/lisp/org-protocol.el
index 2b07a377e..d6cc39aa9 100644
--- a/lisp/org-protocol.el
+++ b/lisp/org-protocol.el
@@ -328,7 +328,7 @@ (defun org-protocol-flatten-greedy (param-list &optional strip-path replacement)
 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 emacsclient's working directory.  This
-function transforms it into a flat list using `org-protocol-flatten' and
+function transforms it into a flat list using `flatten-tree' and
 transforms the elements of that list as follows:
 
 If STRIP-PATH is non-nil, remove the \"/dir/\" prefix from all members of
@@ -343,9 +343,9 @@ (defun org-protocol-flatten-greedy (param-list &optional strip-path replacement)
 `org-protocol-reverse-list-of-files' was set to t and the returned list will
 reflect that.  emacsclient's first parameter will be the first one in the
 returned list."
-  (let* ((l (org-protocol-flatten (if org-protocol-reverse-list-of-files
-				      param-list
-				    (reverse param-list))))
+  (let* ((l (org--flatten-tree (if org-protocol-reverse-list-of-files
+                              param-list
+                            (reverse param-list))))
 	 (trigger (car l))
 	 (len 0)
 	 dir
@@ -368,21 +368,15 @@ (defun org-protocol-flatten-greedy (param-list &optional strip-path replacement)
 	  ret)
       l)))
 
-;; `flatten-tree' was added in Emacs 27.1.
-(defalias 'org-protocol-flatten
-  (if (fboundp 'flatten-tree) 'flatten-tree
-    (lambda (list)
-      "Transform LIST into a flat list.
+(define-obsolete-function-alias 'org-protocol-flatten
+  (if (fboundp 'flatten-tree) 'flatten-tree 'org--flatten-tree)
+  "9.7"
+  "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 list
-	  (if (consp list)
-	      (append (org-protocol-flatten (car list))
-		      (org-protocol-flatten (cdr list)))
-	    (list list))))))
+This function transforms it into a flat list.")
 
 (defun org-protocol-parse-parameters (info &optional new-style default-order)
   "Return a property list of parameters from INFO.
diff --git a/lisp/org-src.el b/lisp/org-src.el
index e1f7d50dc..7edbe0570 100644
--- a/lisp/org-src.el
+++ b/lisp/org-src.el
@@ -208,7 +208,7 @@ (defun org-src--get-known-shells ()
 The shells are associated with `sh-mode'."
   (mapcar
    (lambda (shell) (cons (symbol-name shell) 'sh))
-   (delete-dups (flatten-tree sh-ancestor-alist))))
+   (delete-dups (org--flatten-tree sh-ancestor-alist))))
 
 (defcustom org-src-lang-modes
   `(("C" . c)
-- 
2.25.1