GNU bug report logs -
#74281
30.0.91; font-lock mode hangs on scrolling large Scheme file
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Reported by: Divya Ranjan <divya <at> subvertising.org>
Date: Sat, 9 Nov 2024 16:06:01 UTC
Severity: normal
Found in version 30.0.91
Done: Stefan Monnier <monnier <at> iro.umontreal.ca>
Bug is archived. No further changes may be made.
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Message #29 received at 74281 <at> debbugs.gnu.org (full text, mbox):
Ping! Divya, could you please try Stefan's suggestions and report
back?
> Cc: Divya Ranjan <divya <at> subvertising.org>, 74281 <at> debbugs.gnu.org
> From: Stefan Monnier <monnier <at> iro.umontreal.ca>
> Date: Thu, 14 Nov 2024 11:56:37 -0500
>
> > Stefan, what tools do we have to investigate slowness related to
> > parse-partial-sexp? Or maybe you have suggestions for how to speed up
> > font-lock in this case?
>
> Hmm... `parse-partial-sexp` is normally expected to be fast, unless it
> has to scan a lot of text.
>
> > Here's the profile I get while moving with C-p through the above file:
>
> A stab in the dark, but maybe the relevant call is the one in:
>
> (state (if (or syntax-ppss-table
> (not font-lock--syntax-table-affects-ppss))
> (syntax-ppss start)
> ;; If `syntax-ppss' doesn't have its own syntax-table and
> ;; we have installed our own syntax-table which
> ;; differs from the standard one in ways which affects PPSS,
> ;; then we can't use `syntax-ppss' since that would pollute
> ;; and be polluted by its cache.
> (parse-partial-sexp (point-min) start)))
>
> so the origin of the slowdown would be the (?#. "w 14") in the setting
> below in `scheme.el`:
>
> (setq font-lock-defaults
> '((scheme-font-lock-keywords
> scheme-font-lock-keywords-1 scheme-font-lock-keywords-2)
> nil t (("+-*/.<>=!?$%_&~^:" . "w") (?#. "w 14"))
> beginning-of-defun
> (font-lock-mark-block-function . mark-defun)))
>
> in which case, setting a `syntax-ppss-table` should fix the problem, tho
> we could also fix it by being more careful: AFAICT the purpose of this
> (?#. "w 14") is only to change the syntax of `#` from "prefix" to "word"
> without changing the comment-related flags, so it shouldn't cause
> `font-lock--syntax-table-affects-ppss` to be set.
> So, we could solve it by improving the code that sets
> `font-lock--syntax-table-affects-ppss`, as in the patch below.
>
>
> Stefan
>
>
> diff --git a/lisp/font-lock.el b/lisp/font-lock.el
> index 203131bfd5a..f6299920c0a 100644
> --- a/lisp/font-lock.el
> +++ b/lisp/font-lock.el
> @@ -1955,14 +1955,15 @@ font-lock-set-defaults
> (dolist (char (if (numberp (car selem))
> (list (car selem))
> (mapcar #'identity (car selem))))
> - (unless (memq (car (aref font-lock-syntax-table char))
> - '(1 2 3)) ;"." "w" "_"
> - (setq font-lock--syntax-table-affects-ppss t))
> - (modify-syntax-entry char syntax font-lock-syntax-table)
> - (unless (memq (car (aref font-lock-syntax-table char))
> - '(1 2 3)) ;"." "w" "_"
> - (setq font-lock--syntax-table-affects-ppss t))
> - ))))
> + (let ((old-syntax (aref font-lock-syntax-table char)))
> + (modify-syntax-entry char syntax font-lock-syntax-table)
> + (let ((new-syntax (aref font-lock-syntax-table char)))
> + (unless (and (equal (cdr old-syntax) (cdr new-syntax))
> + (memq (logand (car old-syntax) 255) '(1 2 3 6))
> + (memq (logand (car new-syntax) 255) '(1 2 3 6))
> + (equal (ash (car old-syntax) -8)
> + (ash (car new-syntax) -8)))
> + (setq font-lock--syntax-table-affects-ppss t))))))))
> ;; (nth 4 defaults) used to hold `font-lock-beginning-of-syntax-function',
> ;; but that was removed in 25.1, so if it's a cons cell, we assume that
> ;; it's part of the variable alist.
>
>
>
>
>
This bug report was last modified 140 days ago.
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