mobs::spawn_rules ports SpawnPlacements over a SpawnLevel trait the game's
MobWorld implements: the placement types with per-type isValidSpawn
(leaves, ice, magma for fire-immune types) and isValidEmptySpawnBlock with
each type's dangerous and immune blocks, and every registered predicate in
vanilla's draw order: the dimension's monster light test and block light
limit, thunder, peaceful, spawn reasons, guardians' sky from below water,
drowned, bats, ghasts, ocelots, slimes (surface chance and slime chunks),
strays under powder snow, striders, turtles, polar bears, tropical fish,
nautiluses, silverfish and endermites near players, patrols and the
spawnable-on tags.
Divergences fixed on the way: nether monsters ignored light, hoglins and
piglins had extra checks, slimes spawned outside slime chunks, ocelots and
ghasts skipped their odds, bats ignored the surface and their draw order,
and several predicates read the wrong blocks.
tools/test_spawn_rules_parity.py: 18,669 cases over 87 entity types match.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Ludovic Marie