Concern regarding savegame compatibility came up for similar "Never" support of techs: https://osdn.net/projects/freeciv/ticket/45115#comment:12505:45115:1657972075
Reply To cazfi
Concern regarding savegame compatibility came up for similar "Never" support of techs: https://osdn.net/projects/freeciv/ticket/45115#comment:12505:45115:1657972075
In case of units, it was already impossible to get such units to the game (prevented ruleset load time), and there are flags that can be used to mark unit as unbuildable etc.
Freeciv code often checks if unit tech req is A_NEVER, indicating that the unit isn't in the game at all.
That's relic from the time (obsolete at least 20 years) units were in a static array with fixed order, and those in the middle had to be marked as removed that way. With the current dynamically filled array we don't insert such units at all, and those checks are obsolete.
Get rid of them. Such a use of unit required_advance is also one of the bigger remaining blockers against #44927