[MC-113935] onInitialSpawn modifies world even if mob was not spawned

The bug

The method net.minecraft.entity.EntityLiving.onInitialSpawn(DifficultyInstance, IEntityLivingData) (respectively methods overriding it) modify the world even if the mob the method was called for was not spawned.

How to reproduce

This can currently be seen with MC-103516. The additional mob is spawned but the mob the method was called for is not spawned.

Affected classes

Based on 1.11.2 decompiled using MCP 9.35 rc1

Class	Description
EntitySpider	Spawns skeleton ¹
EntityZombie	Spawns chicken or sets `IsChickenJockey` of existing chicken to `true` ¹
EntityOcelot	Spawns other ocelots

¹ Currently blocked by MC-111747 which describes that position and bounding box are not instantly updated when an entity starts riding another entity

Linked issues

relates to 2

MC-103516 Spider and chicken jockeys only spawn the additional mob Resolved

MC-102018 Team NBT tag adds entity to team even if it was not spawned in the world Reopened

Comments 2

tryashtar 2019-11-02T07:16:27Z

Is this still the case now that MC-103516 is fixed?

marcono1234 2019-11-05T23:46:06Z

It appears in all cases (?) this method is called when the entity will also be spawned in the world. So while this problem still exists in theory, it can currently not happen.