Re: Tracking buffer positions across time, without markers (was Re: PL support)

[Eli Zaretskii <eliz@gnu.org>]

> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> Date: Sun, 10 May 2020 15:27:47 -0400
> 
> The general problem is this: I send the contents of a buffer to a subprocess.  Some time later, the subprocess returns a list of positions (offsets from the beginning of the buffer, or line/column pairs, etc).  At that point, these positions may be stale, since the contents of the buffer may have changed.  I need a way to translate these positions (relative to the old buffer contents) into positions relative to the new buffer contents.

If by the time the output arrives the user have edited the buffer, you
will have to throw the output away, and send a new request.  Rinse,
repeat.  Eventually, the user will stop typing, at least for a short
time, and the output that arrives after that could be used for
fontifying because no changes have been done.  But if this never
happens, i.e. the user keeps being ahead of the subprocess, it would
mean the buffer will not be fontified for a time that is long enough
to be an annoyance.  Which means the solution is not workable.  Right?

IOW, the process of sending whatever you need to send and receiving
the output should be fast enough to be completed before the user types
a lot, or at least short enough to hold off buffer modifications, or
else this is simply not going to work.  Think of the current JIT
font-lock: if it doesn't finish fontifying the current windowful by
the time the user decides to type something, the user will complain,
right?