Subject: 30.2.50; overlay line-prefix display property fighting with text display property
From: JD Smith <[email-masked]>
To: [email-masked]
Date: Tue, 19 Aug 2025 21:39:38 -0400
List-Id: <debbugs-submit.debbugs.gnu.org>

An overlay which applies a line-prefix (e.g. to set the fringe) across several lines conflicts with underlying text which has a replacing display property set.  Evaluate the following in the *scratch* buffer, with at least 3 blank lines at the top of the buffer.

(progn
  (delete-all-overlays)
  (let ((ov (make-overlay 1 4)))
    (overlay-put ov 'line-prefix (propertize "SHOULDNOTSEETHIS" 'display
                                             '(left-fringe right-triangle success))))
  (put-text-property 2 3 'display ">testing fringe display"))

The result is very strange: the SHOULDNOTSEETHIS prefix string appears (sans fringe display), but then vanishes on the next redisplay.  Some (well-balanced) fight between overlay line-prefix display and normal display properties seems to be occurring.