GNU bug report logs - #46177
27.1; Display problem with minibuffer overlay when using display property

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

From: Clemens <clemens.radermacher <at> posteo.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.1; Display problem with minibuffer overlay when using display
 property
Date: Fri, 29 Jan 2021 18:58:46 +0100

When using an overlay with an `after-string` which uses `display`
the prompt background bleeds into the after string:


(set-face-attribute 'minibuffer-prompt nil :background "purple")

(minibuffer-with-setup-hook
    (lambda ()
      (overlay-put
       (make-overlay (point-max) (point-max) nil t t)
       'after-string (propertize " world"
                                 'display
				 " minibuffer")))
  (read-string "Hello"))


While I would expect it to be displayed like when using:


(minibuffer-with-setup-hook
    (lambda ()
      (overlay-put
       (make-overlay (point-max) (point-max) nil t t)
       'after-string " minibuffer"))
  (read-string "Hello"))

Message #8 received at 46177 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Clemens <clemens.radermacher <at> posteo.de>
Cc: 46177 <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1;
 Display problem with minibuffer overlay when using display property
Date: Fri, 29 Jan 2021 20:37:12 +0200

> From: Clemens <clemens.radermacher <at> posteo.de>
> Date: Fri, 29 Jan 2021 18:58:46 +0100
> 
> When using an overlay with an `after-string` which uses `display`
> the prompt background bleeds into the after string:

That's a feature: Emacs treats display strings and overlay strings
differently for the purposes of face merging.

Message #11 received at 46177 <at> debbugs.gnu.org (full text, mbox):

From: Clemens <clemens.radermacher <at> posteo.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 46177 <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1; Display problem with minibuffer overlay when
 using display property
Date: Fri, 29 Jan 2021 21:26:26 +0100

> That's a feature: Emacs treats display strings and overlay strings
> differently for the purposes of face merging.


Okay, thanks. I have a problem with this when displaying completion 
candidates in the minibuffer. The candidates are displayed via 
`after-string` overlay. The candidates are provided by the caller and 
can contain the `display` property. Right now I "inline" any parts of 
the string that use `display` to avoid this:


(defun selectrum--display-string (str)
  "Return display string of STR."
  (let ((len (length str))
        (display "")
        (start 0)
        (end 0))
    (while (not (eq len end))
      (setq end (next-single-property-change start 'display str len))
      (let ((val  (get-text-property start 'display str)))
        (if (and val (stringp val))
            (setq display (concat display val))
          (setq display (concat display (substring str start end)))))
      (setq start end))
    display))


Is there a better way?

Message #14 received at 46177 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Clemens <clemens.radermacher <at> posteo.de>
Cc: 46177 <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1; Display problem with minibuffer overlay when
 using display property
Date: Sat, 30 Jan 2021 10:26:47 +0200

> Cc: 46177 <at> debbugs.gnu.org
> From: Clemens <clemens.radermacher <at> posteo.de>
> Date: Fri, 29 Jan 2021 21:26:26 +0100
> 
> > That's a feature: Emacs treats display strings and overlay strings
> > differently for the purposes of face merging.
> 
> Okay, thanks. I have a problem with this when displaying completion 
> candidates in the minibuffer. The candidates are displayed via 
> `after-string` overlay. The candidates are provided by the caller and 
> can contain the `display` property. Right now I "inline" any parts of 
> the string that use `display` to avoid this:
> 
> 
> (defun selectrum--display-string (str)
>    "Return display string of STR."
>    (let ((len (length str))
>          (display "")
>          (start 0)
>          (end 0))
>      (while (not (eq len end))
>        (setq end (next-single-property-change start 'display str len))
>        (let ((val  (get-text-property start 'display str)))
>          (if (and val (stringp val))
>              (setq display (concat display val))
>            (setq display (concat display (substring str start end)))))
>        (setq start end))
>      display))
> 
> 
> Is there a better way?

Better in what sense?

If you mean a way that prevents the background of the prompt from
being applied to the text you display via the overlay, I think the
best/only way is for the overlay string or display string to specify
the background color.

Message #17 received at 46177 <at> debbugs.gnu.org (full text, mbox):

From: Clemens <clemens.radermacher <at> posteo.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 46177 <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1; Display problem with minibuffer overlay when
 using display property
Date: Sat, 30 Jan 2021 10:30:21 +0100

> Better in what sense?
> 
> If you mean a way that prevents the background of the prompt from
> being applied to the text you display via the overlay, I think the
> best/only way is for the overlay string or display string to specify
> the background color.

Yes, I meant to avoid the issue that the minibuffer prompt face gets
applied to strings defined in the display property. The code I posted
simply removes any strings in the display spec and inlines them, which
seems to work well, too. The problem is not only the background color it 
seems, I would need to completely undo the effects of the minibuffer 
prompt face and I don't know how to do that. But what I'm doing now 
works and if there isn't a better solution I'm fine with using it.

I don't understand the reasons for the current behaviour but please
check out the following which seems not appropriate to me:


(set-face-attribute 'minibuffer-prompt nil :foreground "purple")
(minibuffer-with-setup-hook
    (lambda ()
      (overlay-put
       (make-overlay (point-max) (point-max) nil t t)
       'after-string
       (concat " from"
	           (propertize " world"
			       'display
			       " minibuffer"))))
  (read-string "Hello"))


Even with the " from" string between the string defined in the display 
property gets the prompt face applied.

Message #20 received at 46177 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Clemens <clemens.radermacher <at> posteo.de>
Cc: 46177 <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1; Display problem with minibuffer overlay when
 using display property
Date: Sat, 30 Jan 2021 12:46:11 +0200

> Cc: 46177 <at> debbugs.gnu.org
> From: Clemens <clemens.radermacher <at> posteo.de>
> Date: Sat, 30 Jan 2021 10:30:21 +0100
> 
> The problem is not only the background color it seems, I would need
> to completely undo the effects of the minibuffer prompt face and I
> don't know how to do that.

Use a face which explicitly overrides every attribute of minibuffer
prompt face, I guess?

> (set-face-attribute 'minibuffer-prompt nil :foreground "purple")
> (minibuffer-with-setup-hook
>      (lambda ()
>        (overlay-put
>         (make-overlay (point-max) (point-max) nil t t)
>         'after-string
>         (concat " from"
> 	           (propertize " world"
> 			       'display
> 			       " minibuffer"))))
>    (read-string "Hello"))
> 
> 
> Even with the " from" string between the string defined in the display 
> property gets the prompt face applied.

Because " minibuffer" is a display string, and its buffer position is
still EOB.  That it has the " from " string in the overlay property
before it doesn't change the buffer position whose face affects the
display string.

Message #23 received at 46177 <at> debbugs.gnu.org (full text, mbox):

From: Clemens <clemens.radermacher <at> posteo.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 46177 <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1; Display problem with minibuffer overlay when
 using display property
Date: Sat, 30 Jan 2021 12:09:57 +0100

> Use a face which explicitly overrides every attribute of minibuffer
> prompt face, I guess?

As far as I understand I would have to loop through the overlay string, 
too and apply those face adjustments to every of those display property 
strings. I think then I can also just inline them like in my shown 
example which avoid this issue in the first place.

> 
>> (set-face-attribute 'minibuffer-prompt nil :foreground "purple")
>> (minibuffer-with-setup-hook
>>       (lambda ()
>>         (overlay-put
>>          (make-overlay (point-max) (point-max) nil t t)
>>          'after-string
>>          (concat " from"
>> 	           (propertize " world"
>> 			       'display
>> 			       " minibuffer"))))
>>     (read-string "Hello"))
>>
>>
>> Even with the " from" string between the string defined in the display
>> property gets the prompt face applied.
> 
> Because " minibuffer" is a display string, and its buffer position is
> still EOB.  That it has the " from " string in the overlay property
> before it doesn't change the buffer position whose face affects the
> display string.

Because the " minibuffer" string follows the non affected " from" string
this is unexpected from a caller/UI viewpoint IMO. I don't understand 
the underlying reasoning for this but if you don't think there is 
something to fix here, I will accept that and continue using my workaround.

Message #26 received at 46177 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Clemens <clemens.radermacher <at> posteo.de>
Cc: 46177 <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1; Display problem with minibuffer overlay when
 using display property
Date: Sat, 30 Jan 2021 14:06:56 +0200

> Cc: 46177 <at> debbugs.gnu.org
> From: Clemens <clemens.radermacher <at> posteo.de>
> Date: Sat, 30 Jan 2021 12:09:57 +0100
> 
> Because the " minibuffer" string follows the non affected " from" string
> this is unexpected from a caller/UI viewpoint IMO.

Once Emacs is about to display a 'display' property string, the rules
for which faces are relevant change.

> I don't understand the underlying reasoning for this but if you
> don't think there is something to fix here, I will accept that and
> continue using my workaround.

It's just how Emacs worked since v21, so I think it's too late to
change now.

Message #31 received at 46177-done <at> debbugs.gnu.org (full text, mbox):

From: Clemens <clemens.radermacher <at> posteo.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 46177-done <at> debbugs.gnu.org
Subject: Re: bug#46177: 27.1; Display problem with minibuffer overlay when
 using display property
Date: Sat, 30 Jan 2021 13:10:39 +0100

> It's just how Emacs worked since v21, so I think it's too late to
> change now.

I see, thanks for your discussion and help, I will close this then.

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