bug#15045: Point jumps inappropriately around time of Semantic lexing

[David Engster]

Stefan Monnier writes:
>> The short of it is that I occasionally witness point jump to elsewhere
>> in the buffer while I'm editing and then back again.
>
> So it's "displayed at A" then "displayed at B" then "displayed at
> A again"?  what happens between each one of those 3 displays?
>
> If "nothing", then I suspect there's something like a `sit-for'
> somewhere that causes a redisplay in the middle of the command (i.e. in
> the middle of a save-excursion).

I sometimes see this as well, and yes, "nothing" happens between those
three displays. I also think there's a redisplay triggered by another
background task while Semantic does its idle parsing stuff. I surely
won't rule out that we're missing a save-excursion somewhere in
Semantic, but I think that if this were the case, it should happen much
more often.

I wonder which background tasks could trigger such redisplays. Maybe an
update of the mode-line? How could I debug this? The problem is that
this happens maybe every 15 minutes or so...

-David