bug#70077: An easier way to track buffer changes

[Ihor Radchenko <yantar92@posteo.net>]

Eli Zaretskii <eliz@gnu.org> writes:

> In any case, who and where said the changes will be fetched by
> track-changes-fetch must be in the order they were made? why is the
> order at all significant?

I have concerns that the following API promise can be fulfilled:

    (defun track-changes-fetch (id func)
      "Fetch the pending changes.
    ID is the tracker ID returned by a previous `track-changes-register'.
    FUNC is a function.  It is called with 3 arguments (BEGIN END BEFORE)
    where BEGIN..END delimit the region that was changed since the last
    time `track-changes-fetch' was called and BEFORE is a string containing
                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    the previous content of that region.
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Looking at the implementation of `track-changes--before/after', I can
see that it is updating the BEFORE string and these updates implicitly
assume that the changes arrive in order - which is not true in some edge
cases described in the bug report.

-- 
Ihor Radchenko // yantar92,
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