GNU bug report logs - #42267
Fontification takes a long time when an equation contains a double prime

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

From: Najib Idrissi-Kaïtouni
 <najib.idrissi.kaitouni <at> gmail.com>
To: bug-auctex <at> gnu.org
Subject: Fontification takes a long time when an equation contains a double
 prime
Date: Wed, 8 Jul 2020 14:31:35 +0200

Dear Auctex developers,

Whenever an equation contains a "double prime" '', and if the equation 
is very far down in a long document, it appears that fontification takes 
a very long time. This is not very apparent for short documents, but I 
am currently editing a 6000 lines / 360k character long document. Any 
keystroke resulting in a change in the affected equation, or even just 
displaying that part of the buffer, makes Emacs grind to a halt (on my 
machine, it can take 10-15 seconds to process, during which Emacs is 
completely unresponsive, including not responding to C-g).

I would guess that Auctex thinks '' is the end of a quote and is looking 
for the (nonexistent) double backtick `` that would be the beginning of 
it. I tried to get a backtrace with gdb and it's not exactly clear which 
precise function is to blame, but it was always as part of the 
fontification. As a test, I filled a buffer with some lipsum and put an 
equation at the bottom. Without '' everything is fine, as soon as there 
is a '' in the equation things start to noticeably slow down.

I am currently using the latest version, 12.2.4, and Emacs 27.0.91. The 
behavior is fairly recent, although I couldn't say if it started with 
this release precisely, it may have started more than a week ago.

Thanks.
Najib Idrissi

Message #8 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: Arash Esbati <arash <at> gnu.org>
To: Najib Idrissi-Kaïtouni
 <najib.idrissi.kaitouni <at> gmail.com>
Cc: 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Wed, 08 Jul 2020 22:22:59 +0200

Hi Najib,

Najib Idrissi-Kaïtouni <najib.idrissi.kaitouni <at> gmail.com> writes:

> I would guess that Auctex thinks '' is the end of a quote and is
> looking for the (nonexistent) double backtick `` that would be the
> beginning of it. I tried to get a backtrace with gdb and it's not
> exactly clear which precise function is to blame, but it was always as
> part of the fontification. As a test, I filled a buffer with some
> lipsum and put an equation at the bottom. Without '' everything is
> fine, as soon as there is a '' in the equation things start to
> noticeably slow down.

Can you please share this test file so others can load it and see if the
behavior is reproducible?

> I am currently using the latest version, 12.2.4, and Emacs
> 27.0.91. The behavior is fairly recent, although I couldn't say if it
> started with this release precisely, it may have started more than a
> week ago.

AUCTeX's fontification for math went through a bigger overhaul.  Please
share the file and a recipe (preferably starting with `emacs -Q') how to
trigger your obeservation, that would help a lot.

Thanks in advance, Arash

Message #11 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: Najib Idrissi <najib.idrissi.kaitouni <at> gmail.com>
To: Arash Esbati <arash <at> gnu.org>
Cc: 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Thu, 9 Jul 2020 10:14:47 +0200

[Message part 1 (text/plain, inline)]

Hi,

> Can you please share this test file so others can load it and see if the
> behavior is reproducible?
>
Sure, see the attached file. As I said, it's a file filled with lipsum 
with a single equation at the bottom.

> AUCTeX's fontification for math went through a bigger overhaul.  Please
> share the file and a recipe (preferably starting with `emacs -Q') how to
> trigger your obeservation, that would help a lot.

1. Open the file and go to the equation at the bottom
2. Notice that editing speed inside the equation is normal (e.g. hold
   the space bar inside the equation and notice that it goes at a
   normal speed)
3. Add a double prime somewhere in the equation, e.g. after the 2 so
   that it becomes 1+1=2''
4. Notice that now editing speed is degraded, for example hold the
   space bar at the end of the equation and notice that there is now a
   stutter. If your CPU is too fast and you don't notice the stutter,
   you can just copy more paragraphs of lipsum, I guess.

In my real life example (that I cannot share because the article in 
question is not public yet) the slowdown is so bad that a single 
keystroke inside an affected equation can take several seconds.

Best regards,
Najib Idrissi

Le 08/07/2020 à 22:22, Arash Esbati a écrit :
> Hi Najib,
>
> Najib Idrissi-Kaïtouni <najib.idrissi.kaitouni <at> gmail.com> writes:
>
>> I would guess that Auctex thinks '' is the end of a quote and is
>> looking for the (nonexistent) double backtick `` that would be the
>> beginning of it. I tried to get a backtrace with gdb and it's not
>> exactly clear which precise function is to blame, but it was always as
>> part of the fontification. As a test, I filled a buffer with some
>> lipsum and put an equation at the bottom. Without '' everything is
>> fine, as soon as there is a '' in the equation things start to
>> noticeably slow down.
> Can you please share this test file so others can load it and see if the
> behavior is reproducible?
>
>> I am currently using the latest version, 12.2.4, and Emacs
>> 27.0.91. The behavior is fairly recent, although I couldn't say if it
>> started with this release precisely, it may have started more than a
>> week ago.
> AUCTeX's fontification for math went through a bigger overhaul.  Please
> share the file and a recipe (preferably starting with `emacs -Q') how to
> trigger your obeservation, that would help a lot.
>
> Thanks in advance, Arash

[Message part 2 (text/html, inline)]

[foo.tex (text/x-tex, attachment)]

Message #14 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: Ikumi Keita <ikumi <at> ikumi.que.jp>
To: Najib Idrissi <najib.idrissi.kaitouni <at> gmail.com>
Cc: Arash Esbati <arash <at> gnu.org>, 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Fri, 10 Jul 2020 01:37:25 +0900

[Message part 1 (text/plain, inline)]

Hi Najib,

>>>>> Najib Idrissi <najib.idrissi.kaitouni <at> gmail.com> writes:
> Sure, see the attached file. As I said, it's a file filled with lipsum
> with a single equation at the bottom.

>> AUCTeX's fontification for math went through a bigger overhaul.  Please
>> share the file and a recipe (preferably starting with `emacs -Q') how to
>> trigger your obeservation, that would help a lot.

> 1. Open the file and go to the equation at the bottom
> 2. Notice that editing speed inside the equation is normal (e.g. hold
>    the space bar inside the equation and notice that it goes at a
>    normal speed)
> 3. Add a double prime somewhere in the equation, e.g. after the 2 so
>    that it becomes 1+1=2''
> 4. Notice that now editing speed is degraded, for example hold the
>    space bar at the end of the equation and notice that there is now a
>    stutter. If your CPU is too fast and you don't notice the stutter,
>    you can just copy more paragraphs of lipsum, I guess.

> In my real life example (that I cannot share because the article in
> question is not public yet) the slowdown is so bad that a single
> keystroke inside an affected equation can take several seconds.

Thank you for providing concrete example and procedure to reproduce. I
experience the slowdown you described.

The attached patch fixes, or at least reduces, the slowdown on my side.
Could you check whether it works for you or not?

Best Regards,
Ikumi Keita

[patch (text/x-diff, attachment)]

Message #17 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: Najib Idrissi-Kaïtouni
 <najib.idrissi.kaitouni <at> gmail.com>
To: Ikumi Keita <ikumi <at> ikumi.que.jp>
Cc: Arash Esbati <arash <at> gnu.org>, 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Thu, 9 Jul 2020 19:05:58 +0200

Hi,

Yes, this is much, much better with this patch. I don't experience any 
noticeable slowdown anymore, whether in the test file or in my "real 
world" file. Thanks!

Best regards,
Najib Idrissi

Le 09/07/2020 à 18:37, Ikumi Keita a écrit :
> Hi Najib,
>
>>>>>> Najib Idrissi <najib.idrissi.kaitouni <at> gmail.com> writes:
>> Sure, see the attached file. As I said, it's a file filled with lipsum
>> with a single equation at the bottom.
>>> AUCTeX's fontification for math went through a bigger overhaul.  Please
>>> share the file and a recipe (preferably starting with `emacs -Q') how to
>>> trigger your obeservation, that would help a lot.
>> 1. Open the file and go to the equation at the bottom
>> 2. Notice that editing speed inside the equation is normal (e.g. hold
>>     the space bar inside the equation and notice that it goes at a
>>     normal speed)
>> 3. Add a double prime somewhere in the equation, e.g. after the 2 so
>>     that it becomes 1+1=2''
>> 4. Notice that now editing speed is degraded, for example hold the
>>     space bar at the end of the equation and notice that there is now a
>>     stutter. If your CPU is too fast and you don't notice the stutter,
>>     you can just copy more paragraphs of lipsum, I guess.
>> In my real life example (that I cannot share because the article in
>> question is not public yet) the slowdown is so bad that a single
>> keystroke inside an affected equation can take several seconds.
> Thank you for providing concrete example and procedure to reproduce. I
> experience the slowdown you described.
>
> The attached patch fixes, or at least reduces, the slowdown on my side.
> Could you check whether it works for you or not?
>
> Best Regards,
> Ikumi Keita
>

Message #20 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: Ikumi Keita <ikumi <at> ikumi.que.jp>
To: Najib Idrissi-Kaïtouni <najib.idrissi.kaitouni <at> gmail.com>
Cc: 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Fri, 10 Jul 2020 16:53:39 +0900

[Message part 1 (text/plain, inline)]

Hi Najib and all,

>>>>> Najib Idrissi-Kaïtouni <najib.idrissi.kaitouni <at> gmail.com> writes:
> Yes, this is much, much better with this patch. I don't experience any
> noticeable slowdown anymore, whether in the test file or in my "real
> world" file. Thanks!

Thanks for confirmation. We'll fix the problem soon.

To AUCTeX developers:
I propose to install the attached fix. Any comments and suggestions are
welcome.

[Analysis]
The backgrounds of the problem are the following two:
1. When there is a closing quote (or double prime) '' without matching
   opening quote `` before it, current
   `font-latex-extend-region-backwards-quotation' ends up to decrease
   `font-lock-beg' by 5000 (=default value of
   `font-latex-multiline-boundary') and returns t.
2. Previously, font-latex-extend-region-backwards-* functions were
   stored in `font-latex-extend-region-functions' and called just once
   per fontify operation. However, now they are in
   `font-lock-extend-region-functions' and can be called repeatedly in
   `font-lock-default-fontify-region', until all of them return nil.

Therefore, when there is math expression like $f''(x)=x^{3}$, current
f-l-e-r-b-q repeatedly decreases `font-lock-beg' so that the font lock
region begins with BOB eventually. Thus every key stroke forces to
re-fontify all the region from top of the buffer. This is the reason of
the apparent slowdown in a large buffer.

I think the behavior of the above item 1 is a bug. When f-l-e-r-b-q
cannot find a matching opening quote, it should just give up to extend
the region anymore.

Regards,
Ikumi Keita

[0001-Don-t-extend-font-lock-region-too-much-bug-42267.patch (text/x-diff, attachment)]

Message #23 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: Ikumi Keita <ikumi <at> ikumi.que.jp>
To: 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Sat, 11 Jul 2020 14:55:18 +0900

[Message part 1 (text/plain, inline)]

>>>>> Ikumi Keita <ikumi <at> ikumi.que.jp> writes:
> I think the behavior of the above item 1 is a bug. When f-l-e-r-b-q
> cannot find a matching opening quote, it should just give up to extend
> the region anymore.

After reconsideration, I realized that such giving up is not appropriate
when that unmatched close quote has, in front of it, other open-close
quote pairs. Examples:
      abc ``def ghi'' jkl $y''=x^{2}$
      abc <<def ghi>> jkl $y''=x^{2}$

So the correct way is to continue searching backwards another close
quote, I think. The revised patch is attached. I'll install it soon.

Regards,
Ikumi Keita

[0001-Don-t-extend-font-lock-region-too-eagerly-bug-42267.patch (text/x-diff, attachment)]

Message #26 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: PierGianLuca Porta Mana <pglpm0 <at> gmail.com>
To: 42267 <at> debbugs.gnu.org
Cc: Ikumi Keita <ikumi <at> ikumi.que.jp>
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Sat, 11 Jul 2020 08:37:50 +0200

Hi Ikumi, thank you for taking care of this.

I wonder what other people's opinions would be about turning *off* raw-quotes highlighting by default (is it on by default?) – or maybe eliminating it altogether. There would be several reason for this:

– Quirks with apostrophes used in math mode, as the present bug showed; and also the complexity of distinguishing a genitive apostrophe ("the students' books") from a closing quote mark in a single-quote style, which often occurs in British writings for example.

– Quirks with multi-paragraph quotes, when one uses the quotation style that repeats the opening quotes (but not the closing quotes) at each paragraph.

– Syntactically it's best to introduce quotations with an appropriate macro, eg \enquote{} from the csquotes package, which also automatically takes care of quotation styles like the ones mentioned above.

Just some thoughts.
Cheers,
Luca



On 2020-07-11 07:55, Ikumi Keita wrote:
>>>>>> Ikumi Keita <ikumi <at> ikumi.que.jp> writes:
>> I think the behavior of the above item 1 is a bug. When f-l-e-r-b-q
>> cannot find a matching opening quote, it should just give up to extend
>> the region anymore.
> 
> After reconsideration, I realized that such giving up is not appropriate
> when that unmatched close quote has, in front of it, other open-close
> quote pairs. Examples:
>        abc ``def ghi'' jkl $y''=x^{2}$
>        abc <<def ghi>> jkl $y''=x^{2}$
> 
> So the correct way is to continue searching backwards another close
> quote, I think. The revised patch is attached. I'll install it soon.
> 
> Regards,
> Ikumi Keita
> 
> 
> _______________________________________________
> bug-auctex mailing list
> bug-auctex <at> gnu.org
> https://lists.gnu.org/mailman/listinfo/bug-auctex
> 

Message #29 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: Ikumi Keita <ikumi <at> ikumi.que.jp>
To: PierGianLuca Porta Mana <pglpm0 <at> gmail.com>
Cc: 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Sat, 11 Jul 2020 18:48:43 +0900

Hi PierGianLuca,

>>>>> PierGianLuca Porta Mana <pglpm0 <at> gmail.com> writes:
> I wonder what other people's opinions would be about turning *off*
> raw-quotes highlighting by default (is it on by default?)

Yes, it's on by default, and can be turned off by setting the customize
option `font-latex-quotes' to nil.

> – or maybe eliminating it altogether.
> There would be several reason for this:

> - Quirks with apostrophes used in math mode, as the present bug
> showed; and also the complexity of distinguishing a genitive
> apostrophe ("the students' books") from a closing quote mark in a
> single-quote style, which often occurs in British writings for
> example.

I think those cases don't matter. The default settings of font-latex.el
don't interact with such single apostrophe, and only respond to doubled
apostrophe '' and doubled backquote ``, possibly along with French or
German style quotes. (See the doc string of `font-latex-quote-list'.)

> - Quirks with multi-paragraph quotes, when one uses the quotation
> style that repeats the opening quotes (but not the closing quotes) at
> each paragraph.

If there are many ``s without matching ''s, they are displayed with
warning color. I agree that that warning color would be annoying for
users who have such style of writing. (However, it seems that no users
of AUCTeX complain about it currently. Do you think that there are
potentially many such users actually?)

> - Syntactically it's best to introduce quotations with an appropriate
> macro, eg \enquote{} from the csquotes package, which also
> automatically takes care of quotation styles like the ones mentioned
> above.

Well, I suppose that many users still prefer casual style ``...'' over
\enquote{} etc. because the former is easier to type.


To be honestly :-), the highlighting of ``...'' is not an important
feature for me because most LaTeX documents I encounter are oriented for
math and physics, and have very few ``...''s. So I don't object to
eliminate that feature if a lot of people have opinions to do so.

Regards,
Ikumi Keita

Message #32 received at 42267 <at> debbugs.gnu.org (full text, mbox):

From: PierGianLuca Porta Mana <pglpm0 <at> gmail.com>
To: Ikumi Keita <ikumi <at> ikumi.que.jp>
Cc: 42267 <at> debbugs.gnu.org
Subject: Re: bug#42267: Fontification takes a long time when an equation
 contains a double prime
Date: Sat, 11 Jul 2020 12:48:21 +0200

Hi Ikumi,

I'm actually guilty of both quotation-style sins I mentioned :) But AUCTeX works well for me: as in your case I have turned off fontification for quotes, and have instead activated fontification for the package csquotes (which is also taken care of in preview).

I wanted to put those thoughts out there just in case.

Wish you all a pleasant weekend,
Luca


On 2020-07-11 11:48, Ikumi Keita wrote:

> To be honestly :-), the highlighting of ``...'' is not an important
> feature for me because most LaTeX documents I encounter are oriented for
> math and physics, and have very few ``...''s. So I don't object to
> eliminate that feature if a lot of people have opinions to do so.
> 
> Regards,
> Ikumi Keita
> 

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