Upstream has released updates that appears to apply and compile correctly.
This update has been tested to ensure that World Conversion still occurs correctly.
Bukkit Changes:
0812ce2c SPIGOT-4397: isChunkGenerated API
CraftBukkit Changes:
4824655c SPIGOT-4398: Upgrade to ASM 6.2.1 for better Java 11 support
eea43870 MC-134115: Fix issues converting tile entities
1a7f2d10 SPIGOT-4397: isChunkGenerated API
40aed54d SPIGOT-4396: Improve vehicle movement
Spigot Changes:
f6a273b1 Rebuild patches
This restores Asynchronous Chunk Loading to 1.13, as well as adds Asynchronous Chunk Generation..
This provides a massive boost to server performance and should bring 1.13 back closer to 1.12 performance levels for pre generated worlds.
World Generation will now be faster overall than 1.12 since 1.12 did not have async generation.
**DONATE:**
Lots of effort has went into making this happen. Want to say thanks and donate?
https://donate.emc.gs/AsyncChunks
Aikar