bug#23842: 24.4; Runaway background process

[Ken Brown <kbrown@cornell.edu>]

On 6/27/2016 8:46 AM, Ian Perryman wrote:
> I tried down grading to emacs 24.1.1 in windows to see if the problem
> still exists.
>
> The good news is that the process does not runaway to 100% CPU like with
> emacs 24.4, but it still does not do the completion.  I get the "wrong
> type argument: window-live-p, #<window 5>"
>
> The window # would change as I tried it multiple times.
>
> This appears to the be the same issue that is now reported in emacs 25.
>
> The same error is given in emacs 23.1.1
>
> Not sure when this worked.

I know virtually nothing about how completion works, but a glance at 
verilog-mode.el shows the following code, in both 
verilog-show-completions and verilog-complete-word:

     ;; Show possible completions in a temporary buffer.
     (with-output-to-temp-buffer "*Completions*"
       (display-completion-list allcomp))
     ;; Wait for a key press. Then delete *Completion*  window
     (momentary-string-display "" (point))
     (delete-window (get-buffer-window (get-buffer "*Completions*")))))

It's hard to see how this could possibly work.  As soon as you click in 
the *Completion* window, the window is deleted.  Here's a lisp backtrace:

Debugger entered--Lisp error: (wrong-type-argument window-live-p 
#<window 6>)
   get-char-property(129 follow-link #<window 6>)
   mouse-posn-property((#<window 6> 129 (35 . 76) 415716125 nil 129 (3 . 
4) nil (8 . 4) (9 . 18)) follow-link)
   mouse-on-link-p((#<window 6> 129 (35 . 76) 415716125 nil 129 (3 . 4) 
nil (8 . 4) (9 . 18)))
   mouse--down-1-maybe-follows-link(nil)

The error is generated when Fget_char_property (in textprop.c) calls 
get_char_property_and_overlay, which calls CHECK_LIVE_WINDOW on a window 
that has already been deleted.

Ken