bug#22320: Overlays with an 'invisible property break stacking of overlay faces

["Clément Pit--Claudel" <clement.pitclaudel@live.com>]

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Hi all,

Adding an 'invisible property to an overlay seems to break stacking of faces.
To reproduce, run the following snippet. The whole buffer should have a red
background, but the invisible section does not inherit that background.

(with-current-buffer (get-buffer-create "bug")
  (erase-buffer)
  (fundamental-mode)
  (add-to-invisibility-spec '(outline . t))
  (insert "line1 line2 line3")
  (let ((ov (make-overlay 7 12)))
    (overlay-put ov 'invisible 'outline))
  (let ((ov (make-overlay 7 8)))
    (overlay-put ov 'face '(:underline t)))
  (let ((ov (make-overlay (point-min) (point-max))))
    (overlay-put ov 'face '(:background "red")))
  (pop-to-buffer (current-buffer)))

I initially thought this was an issue of priorities, but removing the overlay with
the invisible property makes the issue disappear. Similarly, removing the
underline overlay makes the issue disappear.

Here is another (more "real-world") way to reproduce this issue (run the
snippet, then use C-x h in the newly created buffer to mark all text: the
invisible section isn't highlighted)

(with-current-buffer (get-buffer-create "org-bug")
  (erase-buffer)
  (org-mode)
  (insert "* line1\n** line2\n* line3")
  (org-shifttab)
  (pop-to-buffer (current-buffer)))

Yet another way it to reproduce it is given below

(with-current-buffer (get-buffer-create "flyspell-bug")
  (erase-buffer)
  (text-mode)
  (add-to-invisibility-spec '(outline . t))
  (insert "line1\nline2\nline3")
  (flyspell-check-region-doublons (point-min) (point-max))
  (let ((ov (make-overlay 7 12)))
    (overlay-put ov 'invisible 'outline))
  (pop-to-buffer (current-buffer)))

Interestingly, the first example is broken in both 24.4 and emacs-25; but the second one is broken only in emacs-25 (the third one does not run in Emacs 24.4).

I wonder if this is connected to another issue that I've seen, where having a composition (using prettify-symbols-mode) just before an invisible region would cause the background of the invisible region to be incorrect, but setting prettify-symbols-unprettify-at-point and moving the point to the edge of the symbol would cause the background to be fine. Unfortunately I don't have a good repro for that issue.

Cheers,
Clément.

In GNU Emacs 25.0.50.8 (x86_64-unknown-linux-gnu, GTK+ Version 3.10.8)
 of 2015-12-29 built on clem-w50-mint
Repository revision: a21bb238ce7bcc9c13a9cf66db77918304daa2fc
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