Roozbeh Pournader <roozbeh@farsiweb.info> writes:
The text of the Iranian law, in effect since 1925, clearly mentions that the true solar year is the measure, and there is no arithmetic leap year calculation involved. There has never been any serious plan to change that law....
Thanks for making this clear. I'll update the tz database accordingly; the only year this affects in the current database is 2025 Gregorian (both spring and fall transitions). I'll add Oscar's comments for years after 2037, as a warning to future maintainers.
I'm not sure about Birashk's suggested leap year rule ... but a very simpler one I checked (using 33-year cycles) will not differ from the astronomical one until sometime in the 2070s.
This suggests that cal-persia.el could be changed as well, as its practical use is (I think) for predicting dates in Iran. I'm hesitant to propose a change myself, though, as I'm not an expert in either the calendar or the code.