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;;; display-fill-column-indicator.el --- interface for display-fill-column-indicator -*- lexical-binding: t -*-
;; Copyright (C) 2019-2025 Free Software Foundation, Inc.
;; Maintainer: emacs-devel@gnu.org
;; Keywords: convenience
;; This file is part of GNU Emacs.
;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs. If not, see <https://www.gnu.org/licenses/>.
;;; Commentary:
;; Provides a minor mode interface for `display-fill-column-indicator'.
;;
;; Toggle display of the column indicator with M-x
;; display-fill-column-indicator-mode. To enable the indicator in
;; all buffers, use M-x global-display-fill-column-indicator-mode.
;; NOTE: Customization variables for
;; `display-fill-column-indicator-column' and
;; `display-fill-column-indicator-character' itself are defined in
;; cus-start.el.
;;; Code:
(defgroup display-fill-column-indicator nil
"Display a fill column indicator in the buffer."
:group 'convenience
:group 'display
:link '(info-link "(emacs)Displaying Boundaries"))
(defcustom display-fill-column-indicator-warning nil
"Highlight fill-column-indicator when current line is too long.
Non-nil means highlight fill-column-indicator when current column exceeds
`display-fill-column-indicator-column'."
:type 'boolean
:version "31.1")
(defface display-fill-column-indicator-warning-face
'((t :inherit error :stipple nil))
"Face used to highlight `display-fill-column-indicator' when lines are too long."
:version "31.1")
(defun fill-indicator--set-warning ()
"Set the warning face for the fill column indicator."
(if-let* ((column (if (integerp display-fill-column-indicator-column)
display-fill-column-indicator-column
fill-column))
((> (save-excursion (end-of-line) (current-column))
column)))
(progn
(face-remap-set-base
'fill-column-indicator
'display-fill-column-indicator-warning-face))
(face-remap-reset-base 'fill-column-indicator)))
;;;###autoload
(define-minor-mode display-fill-column-indicator-mode
"Toggle display of `fill-column' indicator.
This uses `display-fill-column-indicator' internally.
To change the position of the column displayed by default
customize `display-fill-column-indicator-column'. You can change the
character for the indicator setting `display-fill-column-indicator-character'.
The globalized version is `global-display-fill-column-indicator-mode',
which see.
This minor mode assumes the buffer uses a fixed-pitch font; if you
use variable-pitch fonts, the indicators on different lines might
not appear aligned.
See Info node `Displaying Boundaries' for details."
:lighter nil
(if display-fill-column-indicator-mode
(progn
(setq display-fill-column-indicator t)
(unless display-fill-column-indicator-character
(setq display-fill-column-indicator-character
(if (and (char-displayable-p ?\u2502)
(or (not (display-graphic-p))
(eq (aref (query-font (car (internal-char-font nil ?\u2502))) 0)
(face-font 'default))))
?\u2502
?|)))
(if display-fill-column-indicator-warning
(add-hook 'post-command-hook #'fill-indicator--set-warning nil t)))
(if display-fill-column-indicator-warning
(remove-hook 'post-command-hook #'fill-indicator--set-warning t))
(setq display-fill-column-indicator nil)))
(defun display-fill-column-indicator--turn-on ()
"Turn on `display-fill-column-indicator-mode'."
(unless (or (minibufferp)
(and (daemonp) (null (frame-parameter nil 'client))))
(display-fill-column-indicator-mode)))
;;;###autoload
(define-globalized-minor-mode global-display-fill-column-indicator-mode
display-fill-column-indicator-mode display-fill-column-indicator--turn-on
:predicate '((not special-mode) t))
(provide 'display-fill-column-indicator)
;;; display-fill-column-indicator.el ends here
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