Datapacks modifying nether/end generation don't apply properly

[Virenbar]

Expected behavior

Flat terrain to be generated. Version: Paper-325

Observed/Actual behavior

Normal terrain generated. Version: Paper-377

Steps/models to reproduce

1. Add datapack to \<world>\datapack and enable it.
2. Restart server.
3. Generate new terrain.
4. Normal terrain generated instead of flat.

Datapack: FlatOverworld.zip This datapack makes terrain in overworld flat.

Plugin and Datapack List

> plugins [23:58:58 INFO]: Plugins (0): > datapack list [23:59:18 INFO]: There are 3 data packs enabled: [vanilla (built-in)], [file/bukkit (world)], [file/FlatOverworld (world)] [23:59:18 INFO]: There are no more data packs available

Paper version

> version [23:57:24 INFO]: This server is running Paper version git-Paper-377 (MC: 1.17.1) (Implementing API version 1.17.1-R0.1-SNAPSHOT) (Git: 3f17694) You are running the latest version Previous version: git-Paper-325 (MC: 1.17.1)

Other

Server was updated from paper-325 to paper-377 and datapack stopped working. Datapack works in vanilla server.

[Virenbar]

Tested other versions. Paper-335 is latest version in which datapack works. In version 336 datapack has stopped working. It seems PR #6789 broke something.

[jpenilla]

Tested other versions. Paper-335 is latest version in which datapack works. In version 336 datapack has stopped working. It seems PR #6789 broke something.

Just re-tested, and

• Datapacks adding custom dimensions work in Paper 335 and Paper 336
• The datapack linked in the original issue (https://github.com/PaperMC/Paper/files/7515357/FlatOverworld.zip) works in singleplayer, but not on a vanilla server, Paper 335, or Paper 336

It seems like this issue is unrelated to custom dimensions and #6789, but is instead an issue with the vanilla server relating to loading datapacks which modify overworld generation.

[Virenbar]

Also re-tested. All servers were started with datapack enabled and empty ".\world\region" folder.

Screenshots

**Vanilla server** - **Works**  **Paper-335** - **Works**  **Paper-336** - **Not working**  **Paper-master** without 0826-Use-correct-LevelStem-registry-when-loading-default-.patch - **Works** 

[jpenilla]

Something is definitely wrong with your testing setup. Creating a new directory with just server.jar from mojang's site, world/datapacks/FlatOverworld.zip, and eula.txt with eula=true results in the datapack not working. I was unable to get the datapack to successfully modify overworld gen anywhere except singleplayer by adding the datapack from the world creation menu.

In my testing, the vanilla server, Paper 335, Paper 336, Paper master, and paper master with the aforementioned patch reverted all resulted in the same behavior in regards to the datapack not modifying overworld gen from a clean server. I understand you claim otherwise, but before anyone on the team spends any more time on this I think we need confirmation from someone else that this ever worked, as like I already said my testing strongly implies this is a vanilla issue.

[Virenbar]

Here a short video of testing on vanilla server (server.jar, eula.txt, ops.json, startmc.bat with Aikar's Flags)

[Machine-Maker]

maybe the disconnect here is that you are only deleting the region file. when I tested, I deleted everything in the world except the datapacks folder, so the first generation would be with the datapack enabled, but maybe that doesnt work

[Virenbar]

Enabled datapacks saved in level.dat, deleting it disables all datapacks.

[Machine-Maker]

yeah, but all not-recognized datapacks are autoenabled upon server start

[jpenilla]

Enabled datapacks saved in level.dat, deleting it disables all datapacks.

sure, but datapacks are enabled by default when added before starting the server, as opposed to while it's running like in your video

[jpenilla]

Well that's nice, apparently datapacks will show as loaded and enabled when put in the correct location before generating a world, but won't actually work until loading the world a second time, which means you need to delete the region files like in your video...

Now that I'm actually able to get the datapack working on a server, the fix for this was quite simple, but I suspect the nether and end will have a similar problem even after applying my fix.

Given the nature of the bug fixed by the levelstem patch, we basically have to accept that trade off for now, until we can apply a different fix, which will likely need a much bigger diff. The root issue there is that upstream made changes which will effectively cause some worlds to have their seed changed when updating, which is really bad for obvious reasons, so although we would like datapacks to work just as in vanilla in all cases, we need to prioritize not damaging existing worlds.

[jpenilla]

Leaving this open to track the nether/end issue, like I mentioned that will need more work to fix without causing damage to existing worlds due to upstreams amazing code

[Machine-Maker]

So Amaranth mentioned that he thinks datapacks should be/should've been per-world, like almost everything else craftbukkit-related. I feel like its too late to make that change, but thought I'd bring it up cause if we did make them per-world, that might make it easier to fix this issue.

[Athesiel]

So Amaranth mentioned that he thinks datapacks should be/should've been per-world, like almost everything else craftbukkit-related. I feel like its too late to make that change, but thought I'd bring it up cause if we did make them per-world, that might make it easier to fix this issue.

Between having commands run from functions via "execute in [dimension]", the ability to have everything in loot tables specify dimension, and worldgen options already being dimension-driven, i feel like this would probably needlessly complicate things for datapack creators & users alike, like as of 1.18 almost any use in having Anything run per-world can be done with datapacks Or plugins pretty easily save for like, gamerules

[Hwiggy]

This server is running Paper version git-Paper-32 (MC: 1.19) (Implementing API version 1.19-R0.1-SNAPSHOT) (Git: 4c9317c) You are running the latest version Previous version: git-Purpur-1670 (MC: 1.19)

Datapacks in other dimensions are not processed unless you delete region files after level.dat is created