The bug
When loading any structure that contains a double chest, that chest will always load as two independent single chests if the structure is being mirrored. This happens regardless of the orientation of the chest, the direction of the mirroring, and the rotation of the structure.
How to reproduce
/place template minecraft:woodland_mansion/2x2_a2 ~ ~ ~ noneObserve double chests.
/place template minecraft:woodland_mansion/2x2_a2 ~ ~ ~ none left_rightObserve single chests next to each other.
There is a fix in Forge #7803 .
Linked issues
is duplicated by 6
MC-137139
Woodland mansions don't generate double chests
Resolved
MC-153425
Chests generated in the 2x2_a2 ("Large empty storage room") of the woodland mansion doesn't generate as a double chests
Resolved
MC-186511
Mirrored Structures of Structure Blocks don't connect double Chests
Resolved
MC-227260
Double chests do not mirror properly in structures
Resolved
MC-236598
Chest in mansion storage room, are separated.
Resolved
Attachments
Comments 8
Yes, the change is less than a line of code in the ChestBlock class. The mirror function (as named in the official mappings) already exists and just needs the block state updated to swap left and right chest types (a function which also already exists, net.minecraft.world.level.block.state.properties.ChestType.getOpposite in the official mappings).
Confirmed for 1.19.2.
Last time Callum updated this report was 2 years ago, so I'd like to request ownership.
It seems that this happens, because chests' block state don't change the type value based on mirroring in a structure, resulting in an invalid chest (with the connections going outside), which will become single chests because of block updates.
the fix is quite simple: make chests' type values left and right turn to right and left when being mirrored, just like door hinges