bug#16909: 24.3; scrolling *Completions* window with tab sometimes chooses a wrong window

[martin rudalics]

> If the 'other-window-scroll-buffer' is pointing to a dead buffer
> 'scroll-other-window'
> does not fallback to its normal behaviour. You get an 'invalid buffer'
> message.

Hopefully not any more.  Did you try the latest trunk?

> So we don't have to kill the *Completions* buffer. We need to set the
> variable back
> to nil to resume normal user operations after using auto complete scrolling.

We can now kill the *Completions* buffer as well.  We only have to be
sure what's easier - keeping track of `other-window-scroll-buffer' and
resetting it or killing the buffer.  Somewhere there should be a
`quit-restore-window' call around, responsible for accomplishing part of
that task already.

> My investigation was to figure out what is going on, not precisely where to
> fix it and was
> based on semantic's autocomplete which behaves exactly the same. I just
> thought
> that reporting this in base emacs functionality might get a higher chance
> to get
> attention. And the mechanism and a cause seems to be exactly the same.
> I didn't manage to pinpoint where it happens in case of elisp auto complete.
> Only for semantic displayor one (which needs fixing as well).

Then try fixing that.  At the time of displaying the *Completions*
buffer set `other-window-scroll-buffer' to the *Completions* buffer.  At
the time of removing that window (I hope it gets removed) reset
`other-window-scroll-buffer' to nil or kill the *Completions* buffer.

Writing this should be simple once you know where to apply the changes.
The more important task is to give it some testing.

martin