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bug#58122: 28.2; overlay before/after-string does not render more than o
From: |
Josh |
Subject: |
bug#58122: 28.2; overlay before/after-string does not render more than one fringe display spec |
Date: |
Wed, 28 Sep 2022 18:18:57 -0700 |
User-agent: |
Cyrus-JMAP/3.7.0-alpha0-968-g04df58079d-fm-20220921.001-g04df5807 |
On Wed, Sep 28, 2022, at 6:40 AM, Eli Zaretskii wrote:
> tags 58122 wontfix
> thanks
>
>> Date: Tue, 27 Sep 2022 11:05:10 -0700
>> From: "Josh Caswell" <emacs@woolsweater.net>
>>
>> An overlay `before-string' or `after-string' property with both left and
>> right fringe display specs only seems to render the first spec.
>>
>> *Demonstration*:
>> - Launch GUI Emacs with the -q flag
>> - In an Elisp buffer, define these two commands
>>
>> (defun insert-two-squares ()
>> (interactive)
>> (insert (propertize " " 'display [(left-fringe hollow-square)
>> (right-fringe hollow-square)])))
>>
>> (defun overlay-two-squares (right-first)
>> (interactive "P")
>> (remove-overlays)
>> (let ((ov (make-overlay (point) (point)))
>> (specs [(left-fringe hollow-square)
>> (right-fringe hollow-square)]))
>> (overlay-put ov 'before-string
>> (propertize " "
>> 'display
>> (if right-first
>> (reverse specs)
>> specs)))))
>>
>> - Switch to a new test buffer
>> - Invoke `insert-two-squares'; observe that both left and right fringes
>> display a hollow square
>> - Delete the inserted character (fringe bitmaps disappear)
>> - Invoke `overlay-two-squares'; observe that only the left fringe displays a
>> hollow square
>> - Invoke `overlay-two-squares' prefixed with `C-u'; observe that only the
>> _right_ fringe displays the hollow square
>>
>> The same behavior is seen if the overlay property is `after-string' rather
>> than `before-string'.
>>
>> *Expectation*:
>> Based on the display spec documentation I would expect the overlay to render
>> fringes the same way as an inserted propertized string.
>
> Thank you for your report.
>
> This was never supported in Emacs. The reasons are subtle and very
> technical, and I will not go into them here. Making this work as
> expected might be possible, but it would require changes on a very low
> level in the code that handles nested display properties and overlay
> strings, which is already extremely complicated. I find changes of
> such nature unjustified for such a fringe (pun intended) use case.
>
> As an easy work-around, you can have 2 different overlay strings at
> the same position, like this:
Got it. I think this workaround should be sufficient. Thank you for the quick
response!