Resolution: Works As Intended
Affects Version/s: Minecraft 18w11a
Fix Version/s: None
Squids can spawn in waterlogged blocks. I'm not sure whether this is intended or not.
- Create a superflat world (I used the "Redstone Ready" preset)
- Make sure the /gamerule doMobSpawning is set to true
- Set the time to day and make sure you're the only entity in the world
(I suggest you run this while standing on the ground. You can also use any other waterloggable block, I also tested this with oak slabs.)
- Fly away and return to the water to cause the squids to spawn
- If no squids spawned, repeat from step 5.