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(syntax-wholeline-max): New var

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Try and reduce the pain caused by font-lock and syntax-propertize's
wholeline-based operation in buffers made up of a few very long lines
(bug#45898).

* lisp/emacs-lisp/syntax.el (syntax-wholeline-max): New var.
(syntax--lbp): New function.
(syntax-propertize-wholelines): Use it.

* lisp/jit-lock.el (jit-lock--antiblink-post-command): Use `syntax--lbp`.

* lisp/font-lock.el (font-lock-extend-region-wholelines): Rewrite,
using `syntax-propertize-wholelines`.
This commit is contained in:
Stefan Monnier 2022-06-30 13:20:33 -04:00
parent 77e99dcacb
commit 15b2138719
4 changed files with 75 additions and 36 deletions
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46
lisp/emacs-lisp/syntax.el
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@ -124,15 +124,49 @@ When the last position scanned holds the first character of a
otherwise nil. That construct can be a two character comment
delimiter or an Escaped or Char-quoted character."))
(defun syntax-propertize-wholelines (start end)
"Extend the region delimited by START and END to whole lines.
(defvar syntax-wholeline-max 10000
"Maximum line length for syntax operations.
If lines are longer than that, syntax operations will treat them as chunks
of this size. Misfontification may then occur.
This is a tradeoff between correctly applying the syntax rules,
and avoiding major slowdown on pathologically long lines.")
(defun syntax--lbp (&optional arg)
"Like `line-beginning-position' but obeying `syntax-wholeline-max'."
(let ((pos (point))
(res (line-beginning-position arg)))
(cond
((< (abs (- pos res)) syntax-wholeline-max) res)
;; For lines that are too long, round to the nearest multiple of
;; `syntax-wholeline-max'. We use rounding rather than just
;; (min res (+ pos syntax-wholeline-max)) so that repeated calls
;; to `syntax-propertize-wholelines' don't keep growing the bounds,
;; i.e. it really behaves like additional line-breaks.
((< res pos)
(let ((max syntax-wholeline-max))
(max (point-min) (* max (truncate pos max)))))
(t
(let ((max syntax-wholeline-max))
(min (point-max) (* max (ceiling pos max))))))))
(defun syntax-propertize-wholelines (beg end)
"Extend the region delimited by BEG and END to whole lines.
This function is useful for
`syntax-propertize-extend-region-functions';
see Info node `(elisp) Syntax Properties'."
(goto-char start)
(cons (line-beginning-position)
(progn (goto-char end)
(if (bolp) (point) (line-beginning-position 2)))))
;; This let-binding was taken from
;; `font-lock-extend-region-wholelines' where it was used to avoid
;; inf-looping (Bug#21615) but for some reason it was not applied
;; here in syntax.el and was used only for the "beg" side.
(let ((inhibit-field-text-motion t))
(let ((new-beg (progn (goto-char beg)
(if (bolp) beg
(syntax--lbp))))
(new-end (progn (goto-char end)
(if (bolp) end
(syntax--lbp 2)))))
(unless (and (eql beg new-beg) (eql end new-end))
(cons new-beg new-end)))))
(defun syntax-propertize-multiline (beg end)
"Let `syntax-propertize' pay attention to the syntax-multiline property."