D21392 - D21397 contain the non-trivial adjustments for this, on top of that there are simple changes required in akonadi-search, calendarsupport, eventviews, kalarm and kdepim-addons.

This change broke calligra:

/d/kde/src/5/calligra/calligra/plan/src/plugins/filters/icalendar/export/icalendarexport.cpp:143:27: error: ‘Ptr’ is not a member of ‘KCalCore::Person’

KCalCore::Person::Ptr p = KCalCore::Person::fromFullName(node->leader());
                  ^~~

In D21391#500365, @dfaure wrote:

This change broke calligra:

/d/kde/src/5/calligra/calligra/plan/src/plugins/filters/icalendar/export/icalendarexport.cpp:143:27: error: ‘Ptr’ is not a member of ‘KCalCore::Person’
        KCalCore::Person::Ptr p = KCalCore::Person::fromFullName(node->leader());
                          ^~~

Not sure if I'm looking at the same code (path/line numbers don't match), but https://cgit.kde.org/calligraplan.git/tree/src/plugins/filters/icalendar/export/icalendarexport.cpp already seems to have an #ifdef for this (which would need to be extended to the same change in Attendee though).

That's a fork of the code in calligraplan, a separate repository...
But I'll grab that solution, thanks.

Oh, hmm, in calligra/3.1 branch, plan was still in that repo, then it got moved out.

And that's a hack, there's nothing that ever sets that define.... AND the whole code is in #if 0 anyway.

Anyhow, fixed properly. https://commits.kde.org/calligra/2d484fda1b31a72659088a4bfce5c3708e923cb0