bug#23980: 25.0.95; Events put in `unread-command-events' can be wrongly handled

[Dmitry Gutov <dgutov@yandex.ru>]

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On 11/19/17 11:39 AM, Chris Feng wrote:
> The bug was fixed by 1f3f4b1296.

Eli, any change to have this backported to emacs-26?

This reason I'm asking is, this fixed a rather nasty bug resulting from 
the interaction between the newest company-mode (0.9.5) and 
flyspell-mode, both of which use sit-for. This particular combination 
results in a timer being run inside a sit-for, which also calls sit-for, 
which in emacs-26 ends up putting e.g. (t t . 45) into 
unread-command-events.

Here's how to reproduce:

- Visit the attached file.

- M-x eval-buffer.

- Start typing.

- See "<t> is undefined" in the minibuffer for every other keypress.

Originally reported here: 
https://github.com/company-mode/company-mode/issues/760

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(defvar foo-timer nil)

(defun foo-pre-command ()
  (when foo-timer
    (cancel-timer foo-timer)
    (setq foo-timer nil)))

(defun foo-post-command ()
  (run-with-timer 0.01 nil #'foo-idle))

(defun foo-idle ()
  (sit-for 5))

(add-hook 'pre-command-hook 'foo-pre-command)
(add-hook 'post-command-hook 'foo-post-command)

(flyspell-mode)

;; This causes unread-command-events to sometimes contain
;; e.g. ((t t . 45))

mmmmmm