bug#59141: 28.1.90; Face :extend when all the line but trailing \n is invisible

[Juri Linkov]

> Does the below produce what you want?
>
>   (progn
>     (insert "ab")
>     (let ((o (make-overlay 2 3)))
>       (overlay-put o 'after-string "!"))
>     (let ((o (make-overlay 2 3)))
>       (overlay-put o 'invisible t)))

Thanks, this is a possibility.  Maybe not easy to use
since for an ellipsis overlay will need to get the boundaries
of the invisible outline overlay.  Or maybe simpler to put
'after-string' on the same invisible overlay like this:

@@ -973,6 +974,8 @@ outline-flag-region
     ;; belongs to the heading rather than to the entry.
     (let ((o (make-overlay from to nil 'front-advance)))
       (overlay-put o 'evaporate t)
+      (when (eq outline-minor-mode-use-buttons 'ellipsis)
+        (overlay-put o 'after-string "…"))
       (overlay-put o 'invisible 'outline)
       (overlay-put o 'isearch-open-invisible
                   (or outline-isearch-open-invisible-function