The bug
Information about previous structures (generated in the world) saved in data/*.dat files seem not to load when a 1.12.2 and below world is opened with 1.13 (tested on client and server).
How to reproduce
Run 1.12.2 client, create a new world, seed 2791111690993685248
Teleport to about 5256.0 65.0 -248.0
Observe guardians frolicking in the autumn mist
Close 1.12.2
Open 1.13 and enter the world
Fly up to Y190 to let the existing hostiles despawn
Descend to Y60
Observer no more guardians to spawn
Confirm the observation typing
/kill @e[type=minecraft:guardian]
The ability to store previously generated structures, even if the newer world generation/format had different opinion about it, allowed for players with stubborn personalities to continue playing in their old and dingy worlds even in the newest and shiniest of Minecraft versions.
Related issues
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migrated
migrated
Same issue with 18w07c. Loaded 1.12.2 word into snapshot to see new mechanics and how they would affect farms. No guardians spawn in existing guardian farm/temple. Tons of hostile mobs spawning though, so I am assuming the game no longer recognizes this as an ocean monument.
gnembon
I added screenshots what happens if you create a world with said seed and tp to said location for each version separately (18w07c and 1.12.2). 18w07c didn't create Monument.dat file yet the monument generated when teleported to this place. Did the location of saved structures changed?
AceMcCrank
Oh. This should be updated with the more recent versions of 1.13 snapshots. My search, https://bugs.mojang.com/browse/MC-126943?jql=affectedVersion%20in%20(%22Minecraft%2018w10c%22%2C%20%22Minecraft%2018w10d%22)%20AND%20text%20~%20%22structure%22 yielded no results and the versions listed here are not selectable currently in the search options. This happens in 18w10c & 18w10d currently.
pokechu22
Added. It is possible to search for older versions, though, but only on the advanced search; see WEB-929.
migrated
It's generally better to not assume tickets are up to date, limiting the ticket creation range to the last X weeks usually works for new issues.
migrated
To add to this issue, as of 18w15a, witch huts generated in a 1.12.2 world are no longer spawning only witches after conversion (they are spawning other mobs like creepers, skeletons, etc). New witch huts generated by 18w15a's world generation function properly since that was resolved in MC-125141. It's only the converted ones that are broken.
migrated
Just loaded my 1.12 world into the latest snapshot, 18w20c and the witch hut I had been just setting up is no longer spawning witches. I used the /locate witch_hut command and it did locate and point to the witch hut so it does see it. However it no longer functions.
migrated
It seems like it isn't populating the Swamp_Hut entry in the References folder of the chunk in the region file. It's only populating the Swamp_Hut entries under Starts. We didn't have that entry in the Temple.dat previously. Any chance a dev could help us figure out how that References entry is calculated so we can edit the region files to fix it until this is resolved?
migrated
Hey almightyzing. Yep that is the problem, or one of them. Sometimes the "Swamp_Hut" tag is not generated in the "Starts" tag.
The value of the "Swamp_Hut" tag are the chunk coordinates from the witch hut merged into one integer. Click" Hex" in the NBTExplorer then you'll see what I mean.
So 07 00 00 00 00 00 00 00 and 64 00 00 00 00 00 00 00 would give 07 00 00 00 64 00 00 00.
migrated
Here is a twitter link where I explain how to convert old witch hut structures to the 1.13 snapshots.
kumasasa
@unknown, mind to attach the pictures here to this ticket ?
Twitter is no bugtracker...
migrated
Sorry was only meant for helping out. I can edit my post tomorrow, it's getting late here <3
kumasasa
✔
migrated
The structures do not generate completely because when converting from old worlds to the snapshots the value for the reference to the start chunk of the structure is not created. In case of a larger structure such as an ocean monument it applies to all chunks where the structure is included.
[media]Sometimes the "structure tag" is corrupt or do not generate in the start chunk of the structure.
[media]
gnembon