Buried treasure can create invalid block entities when generating in the location same as a block entity

This ticket clones MC-163945.

Can confirm.

I think the issue here is that burried treasure chests can spawn in (not under, in) a mineshaft tunnel in the first place; it would be safer to also make it copy the NBT data of the cloned block, but it shouldn't even spawn on that spot in the first place.

According to @unknown in this comment this is a separate bug:
— Working pig spawners spawn for a different reason, this is not the same bug, they spawn because when a buried tresure spawns, it hides itself by copying the blockstate without nbt data it replaced to it's sides that are air or water, so here i think the bug is that it only copies the blockstate and not the nbt data, and the spawners should be cave spider spawners

This might be why this was not fixed.

MC-163945 was originally about non-functional pig spawners that were created when two dungeons generated next to each other and the chest of one dungeon overlapped the spawner of the other dungeon. The bug about functional pig spawners being created by buried treasure overlapping a cave spider spawner (in a mineshaft) was later added to MC-163945, but apparently, it would have been better for a separate report to have been created instead.

Do we have any examples of this in 1.18+ due to big world generation changes? Seed provided in the description cannot be used to replicate the issue anymore.

The core issue still seems to exist as of 23w35a. To test, follow the steps below:

1. Go to a newly generated chunk, go to 9, ~, 9 (chunk coords) and stand on the ground

/fill ~-2 ~-4 ~-2 ~2 ~4 ~2 air

1. Fly up a few blocks, but don't move in x/z

/execute positioned over world_surface run setblock ~ ~ ~ minecraft:spawner{SpawnData:{entity:{id:"minecraft:cave_spider"}}}

/place structure minecraft:buried_treasure ~ ~ ~

(If the chest was placed under the spawner, run

/execute positioned over world_surface run clone ~-2 ~-1 ~-2 ~2 ~-1 ~2 ~-2 ~-2 ~-2 replace move

and try again)

1. Observe that the buried treasure chest is surrounded on top and to the sides by empty spawners. (Spawners are now empty by default, as opposed to being pig spawners.) This doesn't seem intended; either the spawners should be cave spider spawners, or the game should detect that the block to be replaced is a block entity and use a fallback block instead.

As for whether this issue can still be encountered in the wild, I would assume so but given the extreme rarity of this situation I've never stumbled upon such a case myself. Also, the data mismatch doesn't seem to happen anymore; the worst I was able to get was an empty spawner, which is technically a valid block state, albeit not one that should generate naturally.

I am unable to reproduce this issue, can you confirm that you are still able to reproduce this on the latest version?

I am able to reproduce this issue in 1.21.4 Pre-release 1.