Re: [Bug] org-persist.el: xdg.el is unavailable in emacs-25.2

[Ihor Radchenko <yantar92@gmail.com>]

Max Nikulin <manikulin@gmail.com> writes:

>> In toplevel form:
>> ox-beamer.el:34:1:Error: Cannot open load file: No such file or directory, xdg
>  >
>  > ...
>
> org.el in the main branch still declares
>
>> ;; Package-Requires: ((emacs "25.1"))
>
> but it seems xdg.el used by org-persist.el was added in emacs-26.0.
>
> I do not actually use emacs-25.2, but it happened that I have a test 
> container for Org based on Ubuntu-18.04.
>
> Either org-persist and org-compat should be updated with some 
> compatibility code or required emacs version should be updated once more.

Technically, the current Emacs version is Emacs 27. So, following our
maintenance convention [1], we should support everything down to Emacs
25 (e.g. 27-2). However, Emacs 28 is going to be out soon-ish and the
problem is not on bugfix branch, but only on main. I am not sure if we
need to follow version-2 convention for main as well. Maybe better
require only version-1? Weaker back-compatibility requirement can allow
us to implement more advanced features relying on more recent Emacs
versions.

[1] https://orgmode.org/worg/org-maintenance.html

Also, org-src.el from bugfix may not run on Emacs 25:

In end of data:
org-src.el:1312:1:Warning: the function ‘replace-buffer-contents’ is not known
    to be defined.

Best,
Ihor