Entity spawned in on_step not visible to get_objects_inside_radius

[sfan5]

Minetest version

Minetest 5.9.0-dev 3017b02 (Linux)

Summary

#13880 causes objects spawned during iteration of the object list (so during on_step) to only show up once this iteration ends.
This could be considered a defect. It's not easily fixable.

Steps to reproduce

core.register_entity("test2:a", {
	initial_properties = {
		static_save = false,
		visual = "sprite",
		textures = {"cdb_update.png"},
	},
	on_step = function(self)
		local pos = self.object:get_pos()
		if not self.once then
			local obj = core.add_entity(pos, "test2:b")
			assert(obj ~= nil)
			for _, obj2 in ipairs(core.get_objects_inside_radius(pos, 1)) do
				if obj2:get_luaentity() and obj2:get_luaentity().name == "test2:b" then
					print("found it")
				end
			end
		end
		self.once = true
	end,
})
core.register_entity("test2:b", {
	initial_properties = {
		static_save = false,
		visual = "sprite",
		textures = {"cdb_add.png"},
	},
})

1. do /spawnentity test2:a
2. observe that both entities were spawned
3. look for "found it" line in vain

bonus:
4. change on_step to on_activate
5. re-do and observe that "found it" was printed