bug#35645: Fix icalendar--add-diary-entry/diary-make-entry interaction

[Thomas Fitzsimmons <fitzsim@fitzsim.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Ulf Jasper <ulf.jasper@web.de>
>> Date: Mon, 03 Jun 2019 20:30:13 +0200
>> Cc: 35645@debbugs.gnu.org, Noam Postavsky <npostavs@gmail.com>
>> 
>> Am 23.05.2019 um 22:49 (-0400) schrieb Thomas Fitzsimmons:
>> >
>> > Ulf, the only other feedback I have for icalendar is that
>> > icalendar--add-diary-entry is useful to/used by other packages (e.g.,
>> > Excorporate) despite it being a private function.  What if we added a
>> > public alias, icalendar-add-diary-entry, within this same patch?  Then I
>> > could check for that alias's existence and only enable the workaround
>> > advice for older Emacs versions.
>> >
>> 
>> Could you please provide a patch with all the changes we want to make?
>
> Ping!  Thomas, could you please provide a patch as Ulf requested?  We
> would like to proceed with fixing this issue.

I tried out this approach, mostly to try to preserve
icalendar--add-diary-entry's current default behaviour of showing the
resulting diary buffer.  However, I was wrong about
icalendar-add-diary-entry being called directly; the icalendar entry
point Excorporate calls is icalendar-import-buffer.  So I think the
original patch is fine as-is, as long as Ulf is OK with the change to
icalendar--add-diary-entry's default behaviour, such that it does not
show the modified diary file's buffer (which some third party packages
might rely on).  To determine whether or not to apply the workarounds
I'll check the "arity" of diary-make-entry.

I'll write the change log and push the patch this evening unless I hear
otherwise.

Thanks,
Thomas