bug#22323: Font fallback causes inconsistent stacking of faces in overlays with invisible property

[Clément Pit--Claudel]

Hi all,

Font fallback seems to break face stacking for invisible overlays:

This works fine:

(with-current-buffer (get-buffer-create "No prettification: ellispis is 
highlighed")
  (erase-buffer)
  (fundamental-mode)
  (add-to-invisibility-spec '(outline . t))
  (insert "abc!!def!!ghi")
  (let ((ov (make-overlay 6 9)))
    (overlay-put ov 'invisible 'outline))
  (let ((ov (make-overlay (point-min) (point-max))))
    (overlay-put ov 'face 'region))
  (pop-to-buffer (current-buffer)))

This doesn't work (assuming that ℙ is not in your usual font):

(with-current-buffer (get-buffer-create "No prettification: ellispis is 
highlighed")
  (erase-buffer)
  (fundamental-mode)
  (add-to-invisibility-spec '(outline . t))
  (insert "abcℙℙdefℙℙghi")
  (let ((ov (make-overlay 6 9)))
    (overlay-put ov 'invisible 'outline))
  (let ((ov (make-overlay (point-min) (point-max))))
    (overlay-put ov 'face 'region))
  (pop-to-buffer (current-buffer)))

I came across this while using prettify-symbols-mode:

(with-current-buffer (get-buffer-create "With prettification to common 
character: ellispis is highlighed")
  (erase-buffer)
  (fundamental-mode)
  (add-to-invisibility-spec '(outline . t))
  (insert "abc!!def!!ghi")
  (setq prettify-symbols-alist '(("!!" . ?ℙ)))
  (prettify-symbols-mode)
  (let ((ov (make-overlay 6 9)))
    (overlay-put ov 'invisible 'outline))
  (let ((ov (make-overlay (point-min) (point-max))))
    (overlay-put ov 'face 'region))
  (pop-to-buffer (current-buffer)))

Cheers,
Clément.

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