Partially Generated Chunks are not saved in some situations

Expected behavior

Member of OpenTerrainGenerator dev team here.

We're running into issues with a Minecraft bug: MC-224729. It is causing chunks to be generated twice, which some of our structures don't support.

Observed/Actual behavior

Here are some images of the glitch in action.

The following issues appear in vanilla Minecraft.

Steps/models to reproduce

While you may be able to find this in vanilla, it is easier to see in OTG. Start by loading up an OTG preset using the OTG 1.16.5 Alpha. Wildlands, Biome Bundle, Dregora, etc should all work. Once the spawn chunks are loaded in, stop the server, and then begin exploring around. If you're lucky enough, you'll see some odd chunk borders where structures were cut off.

You can also attempt to find this is a vanilla world but it may be less noticable.

Plugin list

OpenTerrainGenerator 1.16.5 Alpha 0.0.17

Paper version

This server is running Paper version git-Paper-783 (MC: 1.16.5) (Implementing API version 1.16.5-R0.1-SNAPSHOT)
You are running the latest version

Agreements

• I am running the latest version of Paper available from https://papermc.io/downloads.
• I have searched for and ensured there isn't already an open issue regarding this.
• My version of Minecraft is supported by Paper.

Other

Here's the mixins we used to fix the problem on Forge: MixinChunkManager.java

What one of our devs did but for Fabric: MixinThreadedAnvilChunkStorage.java

Start by reviewing the linked MixinChunkManager.java and MixinThreadedAnvilChunkStorage.java implementations, then reproduce the issue with an OpenTerrainGenerator 1.16.5 preset after loading spawn chunks and restarting the server. Done means partially generated chunks are saved and structures are no longer cut off when the area is explored.