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 #8 received at 74281 <at> debbugs.gnu.org (full text, mbox):
> Date: Sat, 09 Nov 2024 16:04:13 +0000
> From: Divya Ranjan via "Bug reports for GNU Emacs,
> the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
>
>
> 1. In emacs -Q, open a fairly big Scheme file (> 70k) and try to move in
> the file with C-n, C-f or mouse scrolling. It sverely lags for several
> seconds, doesn’t even respond to C-g.
I can only reproduce this with C-p when moving from the end of the
file. C-n and C-f are instantaneous here, even though this is an
unoptimized build of Emacs 30.
> 2. Toggle font-lock-mode off through M-x, then try to scroll. It works
> as expected, no serious lags.
>
> 3. Running the profiler also shows font-lock as the culprit.
The profile I measured is below. It seems like the bottleneck is
parse-partial-sexp, which means the syntax table
scheme-mode-syntax-table might be the immediate suspect.
> This makes working on big projects, in my case the source code of GNU
> Guix distribution an impossible situation. I haven’t tried setting up
> (Guile) Scheme with Tree-Sitter, but shouldn’t simple
> syntax-highlighting be not a serious problem?
>
> To try a big Scheme file and reproduce this, open tex.scm in
> gnu/packages/tex.scm in Guix source tree:
>
> https://git.savannah.gnu.org/cgit/guix.git
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?
Here's the profile I get while moving with C-p through the above file:
1151 66% - ...
1151 66% - command-execute
1151 66% - call-interactively
1151 66% - funcall-interactively
1151 66% - previous-line
1151 66% - line-move
798 45% - line-pixel-height
798 45% - jit-lock-function
798 45% - jit-lock-fontify-now
798 45% - jit-lock--run-functions
798 45% - run-hook-wrapped
798 45% - #<byte-code-function CEC>
798 45% - font-lock-fontify-region
798 45% - font-lock-default-fontify-region
798 45% - font-lock-fontify-syntactically-region
798 45% - font-lock-default-fontify-syntactically
798 45% parse-partial-sexp
353 20% - line-move-visual
353 20% - vertical-motion
353 20% - jit-lock-function
353 20% - jit-lock-fontify-now
353 20% - jit-lock--run-functions
353 20% - run-hook-wrapped
353 20% - #<byte-code-function BCE>
353 20% - font-lock-fontify-region
353 20% - font-lock-default-fontify-region
353 20% - font-lock-fontify-syntactically-region
353 20% - font-lock-default-fontify-syntactically
353 20% parse-partial-sexp
585 33% - redisplay_internal (C function)
577 33% - jit-lock-function
577 33% - jit-lock-fontify-now
577 33% - jit-lock--run-functions
577 33% - run-hook-wrapped
577 33% - #<byte-code-function 5A0>
577 33% - font-lock-fontify-region
577 33% - font-lock-default-fontify-region
577 33% - font-lock-fontify-syntactically-region
577 33% - font-lock-default-fontify-syntactically
577 33% parse-partial-sexp
6 0% Automatic GC
This bug report was last modified 140 days ago.
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