bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Evan Moses]

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Emacs version: GNU Emacs 27.0.91 (build 1, x86_64-apple-darwin18.7.0, NS
appkit-1671.60 Version 10.14.6 (Build 18G5033)) of 2020-07-24
Built d5acc509415869bce22c49ae311f2960494a0bdc locally


To reproduce, evaluate this

(set-char-table-range composition-function-table 47
'([".\\(?:\\(?:\\*\\*\\|//\\|==\\)\\|[*/=>]\\)" 0 font-shape-gstring]))

And then evaluate

(setq mode-name "test//")

Emacs will become unresponsive and consume 100% CPU.

-- 
Evan Moses
emoses@gmail.com

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bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Eli Zaretskii]

> From: Evan Moses <emoses@gmail.com>
> Date: Fri, 24 Jul 2020 14:35:50 -0700
> 
> To reproduce, evaluate this
> 
> (set-char-table-range composition-function-table 47 '([".\\(?:\\(?:\\*\\*\\|//\\|==\\)\\|[*/=>]\\)" 0
> font-shape-gstring]))
> 
> And then evaluate 
> 
> (setq mode-name "test//")
> 
> Emacs will become unresponsive and consume 100% CPU.

It doesn't hang here.  Could this be macOS-specific?  Or maybe the
problem happens only with some fonts?  Does it happen in "emacs -Q"?

In any case, did you really mean for Emacs to produce ligatures on the
mode line?  More generally, what kind of ligatures are you trying to
produce with this setup?

bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Robert Pluim]

>>>>> On Sat, 25 Jul 2020 09:24:47 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Evan Moses <emoses@gmail.com>
    >> Date: Fri, 24 Jul 2020 14:35:50 -0700
    >> 
    >> To reproduce, evaluate this
    >> 
    >> (set-char-table-range composition-function-table 47 '([".\\(?:\\(?:\\*\\*\\|//\\|==\\)\\|[*/=>]\\)" 0
    >> font-shape-gstring]))
    >> 
    >> And then evaluate 
    >> 
    >> (setq mode-name "test//")
    >> 
    >> Emacs will become unresponsive and consume 100% CPU.

    Eli> It doesn't hang here.  Could this be macOS-specific?  Or maybe the
    Eli> problem happens only with some fonts?  Does it happen in "emacs -Q"?

I see this on macOS with -Q, which uses Menlo, but only with emacs-27,
not master.. I do see an 'Attempt to shape unibyte text' message from
emacs-27

Robert

bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: Evan Moses <emoses@gmail.com>,  42522@debbugs.gnu.org
> Date: Sat, 25 Jul 2020 19:22:19 +0200
> 
>     Eli> It doesn't hang here.  Could this be macOS-specific?  Or maybe the
>     Eli> problem happens only with some fonts?  Does it happen in "emacs -Q"?
> 
> I see this on macOS with -Q, which uses Menlo, but only with emacs-27,
> not master.. I do see an 'Attempt to shape unibyte text' message from
> emacs-27

Then I guess the problem is already solved on master.

bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Robert Pluim <rpluim@gmail.com>
>> Cc: Evan Moses <emoses@gmail.com>,  42522@debbugs.gnu.org
>> Date: Sat, 25 Jul 2020 19:22:19 +0200
>>
>>     Eli> It doesn't hang here.  Could this be macOS-specific?  Or maybe the
>>     Eli> problem happens only with some fonts?  Does it happen in "emacs -Q"?
>>
>> I see this on macOS with -Q, which uses Menlo, but only with emacs-27,
>> not master.. I do see an 'Attempt to shape unibyte text' message from
>> emacs-27
>
> Then I guess the problem is already solved on master.

Evan, could you please try this on the current master branch?

Best regards,
Stefan Kangas

bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Evan Moses]

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Seems to work fine now; Thanks!

On Wed, Aug 12, 2020 at 5:18 PM Stefan Kangas <stefan@marxist.se> wrote:

> Eli Zaretskii <eliz@gnu.org> writes:
>
> >> From: Robert Pluim <rpluim@gmail.com>
> >> Cc: Evan Moses <emoses@gmail.com>,  42522@debbugs.gnu.org
> >> Date: Sat, 25 Jul 2020 19:22:19 +0200
> >>
> >>     Eli> It doesn't hang here.  Could this be macOS-specific?  Or maybe
> the
> >>     Eli> problem happens only with some fonts?  Does it happen in
> "emacs -Q"?
> >>
> >> I see this on macOS with -Q, which uses Menlo, but only with emacs-27,
> >> not master.. I do see an 'Attempt to shape unibyte text' message from
> >> emacs-27
> >
> > Then I guess the problem is already solved on master.
>
> Evan, could you please try this on the current master branch?
>
> Best regards,
> Stefan Kangas
>


-- 
Evan Moses
emoses@gmail.com

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bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Stefan Kangas]

Evan Moses <emoses@gmail.com> writes:

> Seems to work fine now; Thanks!

Thanks.  I'm therefore closing this bug report.

Best regards,
Stefan Kangas

bug#42522: Emacs 27: 100% CPU when setting mode-name with ligatures

[Evan Moses]

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FYI I was following the instructions here: https://github.com/tonsky/FiraCode/wiki/Emacs-instructions#using-composition-char-table to get Fira Code ligatures globally. It so happens that C-modes will add “//“ to the mode name in certain configurations; I just pared this down to a minimal repro case. 

--
Evan Moses
emoses@gmail.com


> On Jul 24, 2020, at 11:25 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> 
>> 
>> From: Evan Moses <emoses@gmail.com>
>> Date: Fri, 24 Jul 2020 14:35:50 -0700
>> 
>> To reproduce, evaluate this
>> 
>> (set-char-table-range composition-function-table 47 '([".\\(?:\\(?:\\*\\*\\|//\\|==\\)\\|[*/=>]\\)" 0
>> font-shape-gstring]))
>> 
>> And then evaluate 
>> 
>> (setq mode-name "test//")
>> 
>> Emacs will become unresponsive and consume 100% CPU.
> 
> It doesn't hang here.  Could this be macOS-specific?  Or maybe the
> problem happens only with some fonts?  Does it happen in "emacs -Q"?
> 
> In any case, did you really mean for Emacs to produce ligatures on the
> mode line?  More generally, what kind of ligatures are you trying to
> produce with this setup?

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