bug#34771: 27.0.50; object is a window sometimes although it should be a buffer in conditional display spec

bug#34771: 27.0.50; object is a window sometimes although it should be a buffer in conditional display spec

[Tassilo Horn]

The docs state:

,----[ (info "(elisp)Other Display Specs") ]
|    You can make any display specification conditional.  To do that,
| package it in another list of the form ‘(when CONDITION . SPEC)’.  Then
| the specification SPEC applies only when CONDITION evaluates to a
| non-‘nil’ value.  During the evaluation, ‘object’ is bound to the string
| or buffer having the conditional ‘display’ property.  ‘position’ and
| ‘buffer-position’ are bound to the position within ‘object’ and the
| buffer position where the ‘display’ property was found, respectively.
| Both positions can be different when ‘object’ is a string.
`----

So in a conditional display spec, object should always be a buffer.
However, that doesn't seem to be the reality.  Sometimes, it is also a
window.

Here's a recipe for the current master:

$ emacs -q

In *scratch* insert and evaluate:

(insert (propertize "foobar" 'display
		    `(when (get-buffer-window object)
		       . ,(format "%s" (random)))) "\n")

Now move point over the displayed random number, hit and hold C-l, or
do whatever triggers redisplay.

Now I have this in *Messages*:

Error during redisplay: (eval (get-buffer-window object)) signaled (wrong-type-argument stringp #<window 3 on *scratch*>) [33 times]


In GNU Emacs 27.0.50 (build 8, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-03-06 built on thinkpad-t440p
Repository revision: 2260e48d2eeaa9ea2b9c17389cc25d00f85c414c
Repository branch: master
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bug#34771: 27.0.50; object is a window sometimes although it should be a buffer in conditional display spec

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Date: Wed, 06 Mar 2019 18:42:19 +0100
> 
> So in a conditional display spec, object should always be a buffer.

(It could also be a string, although not in your case.)

> However, that doesn't seem to be the reality.  Sometimes, it is also a
> window.
> 
> Here's a recipe for the current master:
> 
> $ emacs -q
> 
> In *scratch* insert and evaluate:
> 
> (insert (propertize "foobar" 'display
> 		    `(when (get-buffer-window object)
> 		       . ,(format "%s" (random)))) "\n")
> 
> Now move point over the displayed random number, hit and hold C-l, or
> do whatever triggers redisplay.
> 
> Now I have this in *Messages*:
> 
> Error during redisplay: (eval (get-buffer-window object)) signaled (wrong-type-argument stringp #<window 3 on *scratch*>) [33 times]

The documentation is correct, but the code had a bug.  I hope I fixed
it now.

Thanks.

bug#34771: 27.0.50; object is a window sometimes although it should be a buffer in conditional display spec

[Tassilo Horn]

Eli Zaretskii <eliz@gnu.org> writes:

>> So in a conditional display spec, object should always be a buffer.
>
> (It could also be a string, although not in your case.)

Right.

>> Now I have this in *Messages*:
>> 
>> Error during redisplay: (eval (get-buffer-window object)) signaled
>> (wrong-type-argument stringp #<window 3 on *scratch*>) [33 times]
>
> The documentation is correct, but the code had a bug.  I hope I fixed
> it now.

I can't tell.  It seems you haven't pushed that change yet.

        Tassilo

bug#34771: 27.0.50; object is a window sometimes although it should be a buffer in conditional display spec

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Cc: 34771@debbugs.gnu.org
> Date: Thu, 07 Mar 2019 11:27:56 +0100
> 
> > The documentation is correct, but the code had a bug.  I hope I fixed
> > it now.
> 
> I can't tell.  It seems you haven't pushed that change yet.

Oops, sorry.  It was a busy evening after an even busier day.  (I did
say "git push", but failed to notice that the push was rejected by the
upstream repository.)

I pushed it now, please take a look.

Btw, if you need your code to work with versions of Emacs before this
bugfix, you can use the following kludgey workaround: if OBJECT is a
window, that stands for the current buffer.

bug#34771: 27.0.50; object is a window sometimes although it should be a buffer in conditional display spec

[Tassilo Horn]

Eli Zaretskii <eliz@gnu.org> writes:

>> > The documentation is correct, but the code had a bug.  I hope I
>> > fixed it now.
>> 
>> I can't tell.  It seems you haven't pushed that change yet.
>
> Oops, sorry.  It was a busy evening after an even busier day.  (I did
> say "git push", but failed to notice that the push was rejected by the
> upstream repository.)
>
> I pushed it now, please take a look.

Yes, it works now.

> Btw, if you need your code to work with versions of Emacs before this
> bugfix, you can use the following kludgey workaround: if OBJECT is a
> window, that stands for the current buffer.

My code has to get the window in order to get the font used to display
BUFFER-POSITION so this bug had positive side-effects for my use-case.
I'll let it in.

Bye,
Tassilo

bug#34771: 27.0.50; object is a window sometimes although it should be a buffer in conditional display spec

[Eli Zaretskii]

> From: Tassilo Horn <tsdh@gnu.org>
> Cc: 34771@debbugs.gnu.org
> Date: Thu, 07 Mar 2019 17:43:53 +0100
> 
> > I pushed it now, please take a look.
> 
> Yes, it works now.

OK, closing.  Thanks.