bug#24585: 25.1; avoid hack in ggtags.el to run compilation-auto-jump timer

[Leo Liu]

,----[ Stefan Monnier ]
| > +      ;; Manually run the `compilation-auto-jump' timer. Hackish but
| > +      ;; everything else seems unreliable. See:
| > +      ;;
| > +      ;; - http://debbugs.gnu.org/13829
| > +      ;; - http://debbugs.gnu.org/23987
| > +      ;; - https://github.com/leoliu/ggtags/issues/89
| > +      ;;
| > +      (pcase (cl-find 'compilation-auto-jump timer-list :key 
#'timer--function)
| > +        (`nil )
| > +        (timer (timer-event-handler timer)))
| 
| I think this deserves a bug report, where we try to figure out how to
| make it possible for ggtags.el to work properly without resorting to such
| a hideous and brittle hack.
| 
| A hack will probably have to stay for compatibility with older Emacsen,
| but we should come up with a better solution for the future.
`----

The hack is due to difficulty in making sure one timer is run before
another that run nearly at the same time. And it's made harder because
timer.el prepends a timer to existing timers running at the same time,
which looks like a mistake.

I think the hack in ggtags.el may be removed by the following patch to
correct the said mistake:

diff --git a/lisp/emacs-lisp/timer.el b/lisp/emacs-lisp/timer.el
index c01ea497..337e1049 100644
--- a/lisp/emacs-lisp/timer.el
+++ b/lisp/emacs-lisp/timer.el
@@ -130,9 +130,9 @@ floating point number."
        (setq delta (time-add delta (list 0 0 (or usecs 0) (or psecs 0)))))
     (time-add time delta)))
 
-(defun timer--time-less-p (t1 t2)
+(defun timer--time-less-or-equal-p (t1 t2)
   "Say whether time value T1 is less than time value T2."
-  (time-less-p (timer--time t1) (timer--time t2)))
+  (not (time-less-p (timer--time t2) (timer--time t1))))
 
 (defun timer-inc-time (timer secs &optional usecs psecs)
   "Increment the time set in TIMER by SECS seconds, USECS microseconds,
@@ -172,7 +172,7 @@ fire repeatedly that many seconds apart."
       (let ((timers (if idle timer-idle-list timer-list))
            last)
        ;; Skip all timers to trigger before the new one.
-       (while (and timers (timer--time-less-p (car timers) timer))
+       (while (and timers (timer--time-less-or-equal-p (car timers) timer))
          (setq last timers
                timers (cdr timers)))
        (if reuse-cell