bug#21824: 25.0.50; overlay modification-hooks called with wrong buffer

[Noam Postavsky]

On Fri, Nov 6, 2015 at 10:23 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> (It sounds like a very old bug, as all the
> pieces of the puzzle were not touched in at least 15 years.)

Quite likely, the circumstances required to trigger it are pretty specific.

>
> Please see if the original bug is solved by the latest master.

Yes, it's fixed.

>
> Btw, any idea how come overlays wound up in *Messages* in the original
> scenario?

global-highlight-parentheses-mode puts overlays in every buffer.

> Actually, would you like converting your test case into a test, and
> post a patch to the test suite to that effect?  TIA.

Something like this? I'm not sure where to put it.

(ert-deftest overlay-modification-hooks ()
  "Test for bug#21824."
  (let ((buf nil))
    (with-temp-buffer
      (insert "123")
      (overlay-put (make-overlay 1 3) 'modification-hooks
                   (list (lambda (ov &rest _)
                           (setq buf (current-buffer)))))
      (goto-char 2)
      (insert "x")
      (with-current-buffer "*Messages*"
        (make-overlay 1 1))
      (message "a message")
      (message "a message")
      (should (eq buf (current-buffer))))))