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* bug#19684: 25.0.50; `this-command` is set to `nil` before `window-scroll-functions` hook runs.
@ 2015-01-25  7:19 Keith David Bershatsky
  2015-01-25 10:38 ` martin rudalics
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: Keith David Bershatsky @ 2015-01-25  7:19 UTC (permalink / raw)
  To: 19684

To the extent that a user wishes to use the value of `this-command` within a function attached to the `window-scroll-functions` hook, a workaround is needed because the default value is `nil`.  In other words, something at the C source code level is setting the value to `nil` before the `window-scroll-functions` hook runs.

There are two (2) workarounds that I am aware of.

1.  Expressly call `redisplay` at the tail end of the series of functions attached to the `post-command-hook`.  Calling `redisplay` somehow prevents `this-command` from being reset to `nil` and the `window-scroll-functions` hook can then take advantage of the existing value of `this-command`.

2.  Create a separate variable -- e.g., `my-this-command` and set the value within a function attached to the `post-command-hook`.  Like so:  (setq my-this-command this-command).  And, then use the value of `my-this-command` within the function attached to the `window-scroll-functions` hook.

The most reliable test I have discovered to pinpoint when the `window-scroll-functions` hook will activate is by having the following code within a function attached to the `post-command-hook`:  (pos-visible-in-window-p (point) (get-buffer-window (current-buffer) (selected-frame))).  If the result is `t`, then the `window-scroll-functions` hook will be activating.

I do not see a visual difference between either of the two workarounds mentioned above, even though I would expect to see a flicker on the screen with the first workaround.  However, there is no flicker.  The second workaround is probably a safer bet.

Although this bug report has been submitted with Emacs Trunk from October 1, 2014; the behavior is the same with Emacs Trunk built on January 1, 2015.

Thanks,

Keith

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In GNU Emacs 25.0.50.1 (x86_64-apple-darwin10.8.0, NS appkit-1038.36 Version 10.6.8 (Build 10K549))
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^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2019-10-01 20:16 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2015-01-25  7:19 bug#19684: 25.0.50; `this-command` is set to `nil` before `window-scroll-functions` hook runs Keith David Bershatsky
2015-01-25 10:38 ` martin rudalics
2015-01-25 15:33 ` Eli Zaretskii
2015-01-25 16:14 ` Stefan Monnier
2015-01-25 17:42 ` Keith David Bershatsky
2019-10-01 20:16 ` Stefan Kangas

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