app-misc/recoll-1.16.2 through to app-misc/recoll-1.19.5 depend on (ics ? dev-python/icalendar) which inherits python. This means that the version of icalendar it may use is icalendar-2.2 which was added (31 Aug 2011), which also means that >=icalendar-3.5, which inherit distutils-r1, have never been usable. Once converted, the dep will require an entry ics ? dev-python/icalendar[${PYTHON_USEDEP}]