GNU bug report logs - #71384
treesit-font-lock-fontify-region unnecessarily re-unfontify's

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: JD Smith <jdtsmith <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: treesit-font-lock-fontify-region unnecessarily re-unfontify's
Date: Wed, 5 Jun 2024 18:06:54 -0400

The function treesit-font-lock-fontify-region in treesit.el calls (font-lock-unfontify-region start end) right away (see below).  But this function is called as the value of font-lock-fontify-syntactically-function from font-lock-default-fontify-region, which has just itself made the exact same call to font-lock-unfontify-region. I commented out that superfluous call in treesit-font-lock-fontify-region and noticed no ill effects.

(defun treesit-font-lock-fontify-region (start end &optional loudly)
  "Fontify the region between START and END.
If LOUDLY is non-nil, display some debugging information."
  (when (or loudly treesit--font-lock-verbose)
    (message "Fontifying region: %s-%s" start end))
  (treesit-update-ranges start end)
  (font-lock-unfontify-region start end)

Message #8 received at 71384 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: JD Smith <jdtsmith <at> gmail.com>, Yuan Fu <casouri <at> gmail.com>
Cc: 71384 <at> debbugs.gnu.org
Subject: Re: bug#71384: treesit-font-lock-fontify-region unnecessarily
 re-unfontify's
Date: Thu, 06 Jun 2024 08:34:13 +0300

> From: JD Smith <jdtsmith <at> gmail.com>
> Date: Wed, 5 Jun 2024 18:06:54 -0400
> 
> The function treesit-font-lock-fontify-region in treesit.el calls (font-lock-unfontify-region start end) right away (see below).  But this function is called as the value of font-lock-fontify-syntactically-function from font-lock-default-fontify-region, which has just itself made the exact same call to font-lock-unfontify-region. I commented out that superfluous call in treesit-font-lock-fontify-region and noticed no ill effects.

Why is that duplicate call a problem?  We don't say that
treesit-font-lock-fontify-region _must_ be called _only_ from
font-lock-default-fontify-region, do we?

Adding Yuan in case he has comments.

Message #11 received at 71384 <at> debbugs.gnu.org (full text, mbox):

From: JD Smith <jdtsmith <at> gmail.com>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Yuan Fu <casouri <at> gmail.com>, 71384 <at> debbugs.gnu.org
Subject: Re: bug#71384: treesit-font-lock-fontify-region unnecessarily
 re-unfontify's
Date: Thu, 6 Jun 2024 07:35:03 -0400

> On Jun 6, 2024, at 1:34 AM, Eli Zaretskii <eliz <at> gnu.org> wrote:
> 
>> From: JD Smith <jdtsmith <at> gmail.com>
>> Date: Wed, 5 Jun 2024 18:06:54 -0400
>> 
>> The function treesit-font-lock-fontify-region in treesit.el calls (font-lock-unfontify-region start end) right away (see below).  But this function is called as the value of font-lock-fontify-syntactically-function from font-lock-default-fontify-region, which has just itself made the exact same call to font-lock-unfontify-region. I commented out that superfluous call in treesit-font-lock-fontify-region and noticed no ill effects.
> 
> Why is that duplicate call a problem?  

I don't know if it's ever really a problem, other than the small amount of time spent removing properties that have just been removed.

> We don't say that treesit-font-lock-fontify-region _must_ be called _only_ from
> font-lock-default-fontify-region, do we?


I presume the same logic would apply to font-lock-fontify-keywords-region, but that does not re-run unfontify (and is obviously much older code).   Maybe treesit reuses treesit-font-lock-fontify-region in non-font-lock contexts?  Feel free to close if Yuan concurs.

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