bug#29854: 25.3; Eshell buffer editing gets slower as colored output grows

[Noam Postavsky]

Pierre Neidhardt <ambrevar@gmail.com> writes:

>> The question is then whether there is some case where using overlays is
>> necessary, or is it just a pessimization?  For reference, I took the
>> text property using definition from man.el (so it at least works for
>> that case):
>
> Any idea what the original intent was?
> I can't seem to see why an overlay would be needed for Eshell's output.

Hard to say.  It might just be a case of going with ansi-color.el's
default.  ansi-color-apply-on-region was changed to use overlays in [1:
0e3c1e3ea6], but it's unclear why.  The commit message just says

    (ansi-color-apply-on-region): Use extents or overlays instead of
    text-properties.

[1: 0e3c1e3ea6]: 2001-01-09 11:38:28 +0000
  (ansi-color-process-output): Use markers instead of positions for start and 
end of region.[...]
  
https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=0e3c1e3ea6a27e20d0252661336afe9fc84b21f5