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;;; reveal.el --- Automatically reveal hidden text at point -*- lexical-binding: t -*-
;; Copyright (C) 2000-2025 Free Software Foundation, Inc.
;; Author: Stefan Monnier <monnier@iro.umontreal.ca>
;; Keywords: outlines
;; 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:
;; Reveal mode is a minor mode that makes sure that text around point
;; is always visible. When point enters a region of hidden text,
;; `reveal-mode' temporarily makes it visible.
;;
;; Overlays can also use the `display' property. For them to be
;; revealed, the `reveal-toggle-invisible' property also has to be
;; present, and should be a function to toggle between having a
;; display property and not.
;;
;; This is normally used in conjunction with `outline-minor-mode',
;; `hs-minor-mode', `hide-ifdef-mode', ...
;;
;; It only works with packages that hide text using overlays.
;; Packages can provide special support for it by placing
;; a function in the `reveal-toggle-invisible' property on the symbol
;; used as the value of the `invisible' overlay property.
;; The function is called right after revealing (or re-hiding) the
;; text with two arguments: the overlay and a boolean that's non-nil
;; if we have just revealed the text. When revealing, that function
;; may re-hide some of the text.
;;; Todo:
;; - find other hysteresis features.
;; - don't hide after a scroll command
;; - delay hiding by a couple seconds (i.e. hide in the background)
;;; Code:
(defgroup reveal nil
"Reveal hidden text on the fly."
:group 'convenience)
(defcustom reveal-around-mark t
"Reveal text around the mark, if active."
:type 'boolean
:group 'reveal)
(defcustom reveal-auto-hide t
"Automatically hide revealed text when leaving it.
If nil, the `reveal-hide-revealed' command can be useful to hide
revealed text manually."
:type 'boolean
:version "28.1")
(defvar-local reveal-open-spots nil
"List of spots in the buffer which are open.
Each element has the form (WINDOW . OVERLAY).")
(defvar-local reveal-last-tick nil)
;; Actual code
(defun reveal-post-command ()
;; Refresh the spots that might have changed.
;; `Refreshing' here means to try and re-hide the corresponding text.
;; We don't refresh everything correctly:
;; - we only refresh spots in the current window.
;; FIXME: do we actually know that (current-buffer) = (window-buffer) ?
(with-local-quit
(with-demoted-errors "Reveal: %s"
(let ((old-ols
(delq nil
(mapcar
(lambda (x)
;; We refresh any spot in the current window as well
;; as any spots associated with a dead window or
;; a window which does not show this buffer any more.
(cond
((eq (car x) (selected-window)) (cdr x))
((not (and (window-live-p (car x))
(eq (window-buffer (car x))
(current-buffer))))
;; Adopt this since it's owned by a window that's
;; either not live or at least not showing this
;; buffer any more.
(setcar x (selected-window))
(cdr x))))
reveal-open-spots))))
(setq old-ols (reveal-open-new-overlays old-ols))
(when reveal-auto-hide
(reveal-close-old-overlays old-ols))))))
(defun reveal-open-new-overlays (old-ols)
(let ((repeat t))
(while repeat
(setq repeat nil)
(dolist (ol (nconc (when (and reveal-around-mark mark-active)
(overlays-at (mark)))
(overlays-at (point))))
(setq old-ols (delq ol old-ols))
(when (overlay-start ol) ;Check it's still live.
;; We either have an invisible overlay, or a display
;; overlay. Always reveal invisible text, but only reveal
;; display properties if `reveal-toggle-invisible' is
;; present.
(let* ((inv (overlay-get ol 'invisible))
(disp (and (overlay-get ol 'display)
(overlay-get ol 'reveal-toggle-invisible)))
(hidden (invisible-p inv))
(ellipsis (and hidden (not (eq t hidden))))
open)
(when (and (or ellipsis disp)
(or (setq open
(or (overlay-get ol 'reveal-toggle-invisible)
(and (symbolp inv)
(get inv 'reveal-toggle-invisible))
(overlay-get
ol 'isearch-open-invisible-temporary)))
(overlay-get ol 'isearch-open-invisible)
(and (consp buffer-invisibility-spec)
(cdr (assq inv buffer-invisibility-spec)))))
(when inv
(overlay-put ol 'reveal-invisible inv))
(push (cons (selected-window) ol) reveal-open-spots)
(if (null open)
(overlay-put ol 'invisible nil)
;; Use the provided opening function and repeat (since the
;; opening function might have hidden a subpart around point
;; or moved/killed some of the overlays).
(setq repeat t)
(condition-case err
(funcall open ol nil)
(error (message "!!Reveal-show (funcall %s %s nil): %s !!"
open ol err)
;; Let's default to a meaningful behavior to avoid
;; getting stuck in an infinite loop.
(setq repeat nil)
(overlay-put ol 'invisible nil))))))))))
old-ols)
(defun reveal-close-old-overlays (old-ols)
(if (or track-mouse ;Don't close in the middle of a click.
(not (eq reveal-last-tick
(setq reveal-last-tick (buffer-modified-tick)))))
;; The buffer was modified since last command: let's refrain from
;; closing any overlay because it tends to behave poorly when
;; inserting text at the end of an overlay (basically the overlay
;; should be rear-advance when it's open, but things like
;; outline-minor-mode make it non-rear-advance because it's
;; a better choice when it's closed).
nil
;; The last command was only a point motion or some such
;; non-buffer-modifying command. Let's close whatever can be closed.
(dolist (ol old-ols)
(if (and (overlay-start ol) ;Check it's still live.
(>= (point) (save-excursion
(goto-char (overlay-start ol))
(line-beginning-position 1)))
(<= (point) (save-excursion
(goto-char (overlay-end ol))
(line-beginning-position 2)))
;; If the application has moved the overlay to some other
;; buffer, we'd better reset the buffer to its
;; original state.
(eq (current-buffer) (overlay-buffer ol)))
;; Still near the overlay: keep it open.
nil
;; Really close it.
(let* ((inv (overlay-get ol 'reveal-invisible))
(open (or (overlay-get ol 'reveal-toggle-invisible)
(get inv 'reveal-toggle-invisible)
(overlay-get ol 'isearch-open-invisible-temporary))))
(if (and (overlay-start ol) ;Check it's still live.
open)
(condition-case err
(funcall open ol t)
(error (message "!!Reveal-hide (funcall %s %s t): %s !!"
open ol err)))
(overlay-put ol 'invisible inv))
;; Remove the overlay from the list of open spots.
(overlay-put ol 'reveal-invisible nil)
(setq reveal-open-spots
(delq (rassoc ol reveal-open-spots)
reveal-open-spots)))))))
(defun reveal-hide-revealed ()
"Hide all revealed text.
If there is revealed text under point, this command does not hide
that text."
(interactive)
(let ((reveal-auto-hide t))
(reveal-post-command)))
(defvar-keymap reveal-mode-map
;; Override the default move-beginning-of-line and move-end-of-line
;; which skips valuable invisible text.
"<remap> <move-beginning-of-line>" #'beginning-of-line
"<remap> <move-end-of-line>" #'end-of-line)
;;;###autoload
(define-minor-mode reveal-mode
"Toggle uncloaking of invisible text near point (Reveal mode).
Reveal mode is a buffer-local minor mode. When enabled, it
reveals invisible text around point.
Also see the `reveal-auto-hide' variable."
:group 'reveal
:lighter (global-reveal-mode nil " Reveal")
:keymap reveal-mode-map
(if reveal-mode
(progn
(setq-local search-invisible t)
(add-hook 'post-command-hook 'reveal-post-command nil t))
(kill-local-variable 'search-invisible)
(remove-hook 'post-command-hook 'reveal-post-command t)))
;;;###autoload
(define-minor-mode global-reveal-mode
"Toggle Reveal mode in all buffers (Global Reveal mode).
Reveal mode renders invisible text around point visible again."
:global t :group 'reveal
(setq-default reveal-mode global-reveal-mode)
(if global-reveal-mode
(progn
(setq search-invisible t)
(add-hook 'post-command-hook 'reveal-post-command))
(setq search-invisible 'open) ;FIXME
(remove-hook 'post-command-hook 'reveal-post-command)))
(provide 'reveal)
;;; reveal.el ends here
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