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* bug#74091: 31.0.50; string-pixel-width in mode line disables region
@ 2024-10-29 17:27 Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors
  2024-10-30 14:59 ` Eli Zaretskii
  0 siblings, 1 reply; 4+ messages in thread
From: Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-29 17:27 UTC (permalink / raw)
  To: 74091



The new implementation of string-pixel-width has some unexpected effect
when it is called from mode-line-format, as happens for example when
mode-line-format-right-align occurs in mode-line-format:

1. emacs -Q
2. (setq-default mode-line-format
	      '("" (:eval (progn (string-pixel-width "foo") nil))))
3. C-x C-f /path/to/emacs/lisp/subr.el
4. C-SPC
5. C-n

At this point the region is expected to be active since we activated it
in step 4.  But in step 5 the mode line is updated, which calls
string-pixel-width, which in turn unexpectedly disables the region.

I'm not really sure why this happens...  Also, if I now trace
string-pixel-width, then it no longer disables the region and everything
starts working as expected.


Thanks,

Eshel





^ permalink raw reply	[flat|nested] 4+ messages in thread

* bug#74091: 31.0.50; string-pixel-width in mode line disables region
  2024-10-29 17:27 bug#74091: 31.0.50; string-pixel-width in mode line disables region Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-30 14:59 ` Eli Zaretskii
  2024-10-30 15:26   ` Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors
  0 siblings, 1 reply; 4+ messages in thread
From: Eli Zaretskii @ 2024-10-30 14:59 UTC (permalink / raw)
  To: Eshel Yaron; +Cc: 74091

> Date: Tue, 29 Oct 2024 18:27:05 +0100
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> 
> 
> The new implementation of string-pixel-width has some unexpected effect
> when it is called from mode-line-format, as happens for example when
> mode-line-format-right-align occurs in mode-line-format:
> 
> 1. emacs -Q
> 2. (setq-default mode-line-format
> 	      '("" (:eval (progn (string-pixel-width "foo") nil))))
> 3. C-x C-f /path/to/emacs/lisp/subr.el
> 4. C-SPC
> 5. C-n
> 
> At this point the region is expected to be active since we activated it
> in step 4.  But in step 5 the mode line is updated, which calls
> string-pixel-width, which in turn unexpectedly disables the region.

Thanks, should be fixed now.

> I'm not really sure why this happens...

It happens because string-pixel-width modifies a buffer, and that sets
deactivate-mark, which then causes the region to be deactivated when
a command finishes.  When you inject string-pixel-width into
mode-line-format, you indirectly cause it to be called from C-n and
the like, because those evaluate the mode-line format.  So doing that
is quite a risky thing, in general.





^ permalink raw reply	[flat|nested] 4+ messages in thread

* bug#74091: 31.0.50; string-pixel-width in mode line disables region
  2024-10-30 14:59 ` Eli Zaretskii
@ 2024-10-30 15:26   ` Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors
  2024-10-30 16:01     ` Eli Zaretskii
  0 siblings, 1 reply; 4+ messages in thread
From: Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors @ 2024-10-30 15:26 UTC (permalink / raw)
  To: Eli Zaretskii; +Cc: 74091

Hi Eli,

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Tue, 29 Oct 2024 18:27:05 +0100
>> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> 
>> 
>> The new implementation of string-pixel-width has some unexpected effect
>> when it is called from mode-line-format, as happens for example when
>> mode-line-format-right-align occurs in mode-line-format:
>> 
>> 1. emacs -Q
>> 2. (setq-default mode-line-format
>> 	      '("" (:eval (progn (string-pixel-width "foo") nil))))
>> 3. C-x C-f /path/to/emacs/lisp/subr.el
>> 4. C-SPC
>> 5. C-n
>> 
>> At this point the region is expected to be active since we activated it
>> in step 4.  But in step 5 the mode line is updated, which calls
>> string-pixel-width, which in turn unexpectedly disables the region.
>
> Thanks, should be fixed now.

Great!  That seems to work.

>> I'm not really sure why this happens...
>
> It happens because string-pixel-width modifies a buffer, and that sets
> deactivate-mark, which then causes the region to be deactivated when
> a command finishes.

Hmm but string-pixel-width used to modify a buffer also in the old
implementation, and that never caused this issue...  And in both the old
implementation and in the new one, the modification is in a different
buffer, is that expected to disable the mark in the original buffer?

> When you inject string-pixel-width into mode-line-format, you
> indirectly cause it to be called from C-n and the like, because those
> evaluate the mode-line format.  So doing that is quite a risky thing,
> in general.

Well, that's how Emacs implements mode-line-format-right-align :)


Thanks for the quick response,

Eshel





^ permalink raw reply	[flat|nested] 4+ messages in thread

* bug#74091: 31.0.50; string-pixel-width in mode line disables region
  2024-10-30 15:26   ` Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors
@ 2024-10-30 16:01     ` Eli Zaretskii
  0 siblings, 0 replies; 4+ messages in thread
From: Eli Zaretskii @ 2024-10-30 16:01 UTC (permalink / raw)
  To: Eshel Yaron; +Cc: 74091-done

> From: Eshel Yaron <me@eshelyaron.com>
> Cc: 74091@debbugs.gnu.org
> Date: Wed, 30 Oct 2024 16:26:38 +0100
> 
> >> At this point the region is expected to be active since we activated it
> >> in step 4.  But in step 5 the mode line is updated, which calls
> >> string-pixel-width, which in turn unexpectedly disables the region.
> >
> > Thanks, should be fixed now.
> 
> Great!  That seems to work.

Thanks for testing, I will close this bug.

> >> I'm not really sure why this happens...
> >
> > It happens because string-pixel-width modifies a buffer, and that sets
> > deactivate-mark, which then causes the region to be deactivated when
> > a command finishes.
> 
> Hmm but string-pixel-width used to modify a buffer also in the old
> implementation, and that never caused this issue...

The new implementation also didn't cause this issue in some buffers.
For example, in *scratch*.  Trying to understand the logic of a bug is
never a good investment of time.

> And in both the old
> implementation and in the new one, the modification is in a different
> buffer, is that expected to disable the mark in the original buffer?

The variable deactivate-mark only becomes buffer-local if set;
otherwise the global value will be changed.

> > When you inject string-pixel-width into mode-line-format, you
> > indirectly cause it to be called from C-n and the like, because those
> > evaluate the mode-line format.  So doing that is quite a risky thing,
> > in general.
> 
> Well, that's how Emacs implements mode-line-format-right-align :)

One reason why I don't like it.  mode-line-format is evaluated in many
more contexts than most people realize, so putting arbitrary calls
there without a good understanding what those calls do and how is not
the best idea, although it will mostly work.





^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2024-10-30 16:01 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2024-10-29 17:27 bug#74091: 31.0.50; string-pixel-width in mode line disables region Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-30 14:59 ` Eli Zaretskii
2024-10-30 15:26   ` Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors
2024-10-30 16:01     ` Eli Zaretskii

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