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+;;; doasedit.el --- Automatic doasedit major-mode detection -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026  Thomas Voss
+
+;; Author: Thomas Voss <mail@thomasvoss.com>
+;; Maintainer: Thomas Voss <mail@thomasvoss.com>
+;; URL: https://git.thomasvoss.com/doasutils
+;; Package-Version: 1.0.0
+;; Package-Requires: ((emacs "24.4"))
+;; Keywords: tools, convenience, files
+
+;; This file is NOT part of GNU Emacs.
+
+;;; License:
+;;
+;; Permission to use, copy, modify, and distribute this software for any
+;; purpose with or without fee is hereby granted, provided that the above
+;; copyright notice and this permission notice appear in all copies.
+;;
+;; THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+;; WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+;; WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+;; AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+;; DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA
+;; OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+;; TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+;; PERFORMANCE OF THIS SOFTWARE.
+;;; Commentary:
+;;
+;; This package provides `global-doasedit-mode', a minor-mode that
+;; ensures that the correct major-mode is set in the current buffer when
+;; editing files via the `doasedit' command-line utility.
+
+;;; Code:
+
+(defgroup doasedit nil
+  "Automatic major-mode detection when editing files via doasedit."
+  :group 'tools)
+
+(defun doasedit--setup-buffer ()
+  (let* ((tmpdir (or (getenv "TMPDIR") "/tmp"))
+         (regexp (expand-file-name "\\`doasedit\\.")))
+    (when (and buffer-file-name (string-match-p regexp buffer-file-name))
+      (if-let ((target-file (getenv "DOASEDIT_EDITING")))
+          (let ((buffer-file-name target-file))
+            (set-auto-mode)
+            (rename-buffer (format "*doasedit: %s*" target-file) :unique))
+        (error "`DOASEDIT_EDITING' is not set.")))))
+
+;;;###autoload
+(define-minor-mode global-doasedit-mode
+  "Global minor-mode to automatically set correct major-mode in the
+current buffer when editing a root-protected file via the doasedit
+command-line utility."
+  :global t
+  :lighter nil
+  (if global-doasedit-mode
+      (add-hook 'find-file-hook #'doasedit--setup-buffer)
+    (remove-hook 'find-file-hook #'doasedit--setup-buffer)))
+
+(provide 'doasedit)
+;;; doasedit.el ends here