GNU bug report logs - #33435
27.0.50; A use case for recursive display specifications

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Pip Cet <pipcet <at> gmail.com>
Subject: bug#33435: closed (Re: bug#33435: 27.0.50; A use case for
 recursive display specifications)
Date: Thu, 03 Oct 2019 16:44:02 +0000

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Your bug report

#33435: 27.0.50; A use case for recursive display specifications

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 33435 <at> debbugs.gnu.org.

-- 
33435: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=33435
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Stefan Kangas <stefan <at> marxist.se>
To: Pip Cet <pipcet <at> gmail.com>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 33435-done <at> debbugs.gnu.org
Subject: Re: bug#33435: 27.0.50;
 A use case for recursive display specifications
Date: Thu, 3 Oct 2019 18:42:48 +0200

skrev Pip Cet <pipcet <at> gmail.com> writes:

> On Thu, Oct 3, 2019 at 12:20 AM Stefan Kangas <stefan <at> marxist.se> wrote:
> > Is this feature request still relevant, or did Eli's reply solve this
> > use case?  Thanks.
>
> I think we can close this bug. It would be nice to have a way to do
> this without using overlays or modifying buffer text (the latter of
> which is what I ended up doing), but hopefully new ideas for how to
> handle overlay/text properties will take care of that one day...
>
> Thanks!

Thank you for clarifying!  Closing now.

Best regards,
Stefan Kangas

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From: Pip Cet <pipcet <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.0.50; A use case for recursive display specifications
Date: Mon, 19 Nov 2018 18:51:37 +0000

This is a feature request: I'd like to be able to display an empty line
as a non-empty line with images in it.

If there's a way to do that with standard display specs, I haven't
found it. It's possible I'm merely missing an obvious way to do so.

I think there are two almost-equivalent approaches to achieving this:

1. interpret a list of display specifications by displaying the first
element of the list, then the second, and so, on, so I could use
(put-text-property beg end 'display `(,image1 ,image2 ,image3 "\n"))

2. allow a single level of recursion in display specifications, so I
could use
(put-text-property beg end 'display (concat (propertize " " 'display
image1) (propertize " " 'display image2) (propertize " " 'display
image3) "\n"))

I've tried simply disabling the checks for recursive display
specifications and (2) appears to work, but I don't know the precise
rationale for their existence, so it's possible that breaks the display
engine somehow.

If the problem is merely the possibility of creating an infinite loop
by setting a string's display property to the string itself (indeed,
in my test build, that crashes emacs), that could be avoided while
still allowing a single level of recursion.

(I'm using this to highlight syntactic indentation with SVG images,
and that's much prettier if empty lines are interpreted as being
indented to the minimum of the preceding and following levels of
indentation, rather than merely being empty.)

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