;;; refill.el --- `auto-fill' by refilling paragraphs on changes -*- lexical-binding: t -*-
;; Copyright (C) 2000-2024 Free Software Foundation, Inc.
;; Author: Dave Love <fx@gnu.org>
;; Maintainer: Miles Bader <miles@gnu.org>
;; Keywords: wp
;; 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 mode where paragraphs are refilled after changes in them
;; (using `after-change-functions'). This gives something akin to typical
;; word processor-style filling. We restrict refilling due to
;; self-insertion to the characters which trigger auto-fill.
;; It partly satisfies a todo item in enriched.el for some value of
;; `without slowing down editing too much'. It doesn't attempt to do
;; anything (using `window-size-change-functions'?) about resizing
;; windows -- who cares?
;; This implementation is probably fragile and missing some special
;; cases -- not extensively tested. Yanking paragraph breaks, for
;; instance, won't DTRT by refilling all the relevant paragraphs.
;; You could do it a bit more efficiently (and robustly?) with just an
;; auto-fill function, but that doesn't cope with changes other than
;; through self-insertion. (Using auto-fill and after-change
;; functions together didn't seem winning.) This could probably
;; benefit from a less-general and faster `fill-paragraph-function',
;; ideally as a primitive.
;; The work is done in a local post-command hook but only if
;; `refill-doit' has been set by the after-change function. Using
;; `post-command-hook' ensures simply that refilling only happens
;; once per command.
;; [Per Abrahamsen's maniac.el does a similar thing, but operates from
;; post-command-hook. I don't understand the statement in it that
;; after-change-functions don't work for this purpose; perhaps there was
;; some Emacs bug at the time. ISTR maniac has problems with
;; whitespace at the end of paragraphs.]
;;; Todo/Bugs:
;; - When deleting the first word on a line, the space after that word tends
;; to become part of the fill-prefix, causing either wrong filling of the
;; remaining text, or causing the cursor to move unexpectedly. Ex:
;; Start with
;; I>< blabla
;;
;; and hit backspace. We end up with
;;
;; ><blabla
;; instead of
;; >< blabla
;;
;; Other example. Start with
;;
;; Foo bar blablabla asdgf
;; word>< asdfas dfasdfasd
;; asd asdfa sdfasd sdf
;;
;; and hit M-backspace. We end up with
;;
;; Foo bar blablabla asdgf
;; ><asdfas dfasdfasd asd
;; asdfa sdfasd sdf
;;; Code:
(defvar-local refill-ignorable-overlay nil
"Portion of the most recently filled paragraph not needing filling.
This is used to optimize refilling.")
(defun refill-adjust-ignorable-overlay (overlay afterp beg _end &optional _len)
"Adjust OVERLAY to not include the about-to-be-modified region."
(when (not afterp)
(save-excursion
(goto-char beg)
(forward-line -1)
(if (<= (point) (overlay-start overlay))
;; Just get OVERLAY out of the way
(move-overlay overlay (point-min) (point-min))
;; Make overlay contain only the region
(move-overlay overlay (overlay-start overlay) (point))))))
(defun refill-fill-paragraph-at (pos &optional arg)
"Like `fill-paragraph' at POS, but don't delete whitespace at paragraph end."
(save-excursion
(goto-char pos)
;; FIXME: forward-paragraph seems to disregard `use-hard-newlines',
;; leading to excessive refilling and wrong choice of fill-prefix.
;; might be a bug in my paragraphs.el.
(forward-paragraph)
(skip-syntax-backward "-")
(let ((end (point))
(beg (progn (backward-paragraph) (point)))
(obeg (overlay-start refill-ignorable-overlay))
(oend (overlay-end refill-ignorable-overlay)))
(unless (> beg pos) ;Don't fill if point is outside the paragraph.
(goto-char pos)
(if (and (>= beg obeg) (< beg oend))
;; Limit filling to the modified tail of the paragraph.
(let ( ;; When adaptive-fill-mode is enabled, the filling
;; functions will attempt to set the fill prefix from
;; the fake paragraph bounds we pass in, so set it
;; ourselves first, using the real paragraph bounds.
(fill-prefix
(if (and adaptive-fill-mode
(or (null fill-prefix) (string= fill-prefix "")))
(fill-context-prefix beg end)
fill-prefix))
;; Turn off adaptive-fill-mode temporarily
(adaptive-fill-mode nil))
(save-restriction
(if use-hard-newlines
(fill-region oend end arg)
(fill-region-as-paragraph oend end arg)))
(move-overlay refill-ignorable-overlay obeg (point)))
;; Fill the whole paragraph
(save-restriction
(if use-hard-newlines
(fill-region beg end arg)
(fill-region-as-paragraph beg end arg)))
(move-overlay refill-ignorable-overlay beg (point)))))))
(defun refill-fill-paragraph (arg)
"Like `fill-paragraph' but don't delete whitespace at paragraph end."
(refill-fill-paragraph-at (point) arg))
(defvar-local refill-doit nil
"Non-nil tells `refill-post-command-function' to do its processing.
Set by `refill-after-change-function' in `after-change-functions' and
unset by `refill-post-command-function' in `post-command-hook', and
sometimes `refill-pre-command-function' in `pre-command-hook'. This
ensures refilling is only done once per command that causes a change,
regardless of the number of after-change calls from commands doing
complex processing.")
(defun refill-after-change-function (_beg end _len)
"Set `refill-doit'. Used by `after-change-functions'."
(unless undo-in-progress
(setq refill-doit end)))
(defun refill-post-command-function ()
"Post-command function to do refilling (conditionally)."
(when refill-doit ; there was a change
;; There's probably scope for more special cases here...
(pcase this-command
('self-insert-command
;; Treat self-insertion commands specially, since they don't
;; always reset `refill-doit' -- for self-insertion commands that
;; *don't* cause a refill, we want to leave it turned on so that
;; any subsequent non-modification command will cause a refill.
(when (aref auto-fill-chars (char-before))
;; Respond to the same characters as auto-fill (other than
;; newline, covered below).
(refill-fill-paragraph-at refill-doit)
(setq refill-doit nil)))
((or 'quoted-insert 'fill-paragraph 'fill-region) nil)
((or 'newline 'newline-and-indent 'open-line 'indent-new-comment-line
'default-indent-new-line 'reindent-then-newline-and-indent)
;; Don't zap what was just inserted.
(save-excursion
(beginning-of-line) ; for newline-and-indent
(skip-chars-backward "\n")
(save-restriction
(narrow-to-region (point-min) (point))
(refill-fill-paragraph-at refill-doit)))
(widen)
(save-excursion
(skip-chars-forward "\n")
(save-restriction
(narrow-to-region (line-beginning-position) (point-max))
(refill-fill-paragraph-at refill-doit))))
(_
(refill-fill-paragraph-at refill-doit)))
(setq refill-doit nil)))
(defun refill-pre-command-function ()
"Pre-command function to do refilling (conditionally)."
(when (and refill-doit (not (eq this-command 'self-insert-command)))
;; A previous setting of `refill-doit' didn't result in a refill,
;; because it was a self-insert-command. Since the next command is
;; something else, do the refill now.
(refill-fill-paragraph-at refill-doit)
(setq refill-doit nil)))
(defvar refill-saved-state nil)
;;;###autoload
(define-minor-mode refill-mode
"Toggle automatic refilling (Refill mode).
Refill mode is a buffer-local minor mode. When enabled, the
current paragraph is refilled as you edit. Self-inserting
characters only cause refilling if they would cause
auto-filling.
For true \"word wrap\" behavior, use `visual-line-mode' instead."
;; Not global, so no effect.
;;; :group 'refill
:lighter " Refill"
:keymap '(("\177" . backward-delete-char-untabify))
;; Remove old state if necessary
(when refill-ignorable-overlay
(delete-overlay refill-ignorable-overlay)
(kill-local-variable 'refill-ignorable-overlay))
(when (local-variable-p 'refill-saved-state)
(dolist (x refill-saved-state)
(set (make-local-variable (car x)) (cdr x)))
(kill-local-variable 'refill-saved-state))
(if refill-mode
(progn
(add-hook 'after-change-functions #'refill-after-change-function nil t)
(add-hook 'post-command-hook #'refill-post-command-function nil t)
(add-hook 'pre-command-hook #'refill-pre-command-function nil t)
(setq-local refill-saved-state
(mapcar (lambda (s) (cons s (symbol-value s)))
'(fill-paragraph-function auto-fill-function)))
;; This provides the test for recursive paragraph filling.
(setq-local fill-paragraph-function #'refill-fill-paragraph)
;; When using justification, doing DEL on 2 spaces should remove
;; both, otherwise, the subsequent refill will undo the DEL.
(setq-local backward-delete-char-untabify-method 'hungry)
(setq refill-ignorable-overlay (make-overlay 1 1 nil nil t))
(overlay-put refill-ignorable-overlay 'modification-hooks
'(refill-adjust-ignorable-overlay))
(overlay-put refill-ignorable-overlay 'insert-behind-hooks
'(refill-adjust-ignorable-overlay))
(auto-fill-mode 0))
(remove-hook 'after-change-functions #'refill-after-change-function t)
(remove-hook 'post-command-hook #'refill-post-command-function t)
(kill-local-variable 'backward-delete-char-untabify-method)))
(provide 'refill)
;;; refill.el ends here