The upgrade path to update outdated structures for the flattening is missing

Sorry this is impossible. You are going to have to load them in a 1.12 world, load that world in 1.13 and export them again.

ok i understand and the flower pot have a missing texture.

Can I just double check that this problem has been understood correctly since various other bug reports are being resolved as duplicates of this one.

From what I can tell, this is not a report that user-generated structure files are not being upgraded automatically (which is understandably impossible) but that the structures included with the game (Woodland Mansion, Igloo, etc.) have not been updated to reflect the flattened block data and hence do not generate properly. The image supplied is of a woodland mansion with most of the wood blocks missing.

I believe Tim Stubberfield is correct. I have several worlds I created in 17w47a and b with woodland mansions (as well as ocean monuments, end cities, and igloos) which have missing blocks. All the blocks missing are blocks that were variants of another type of block in 1.12. These include dark oak planks, magenta banners, wet sponges, etc.) Although it is impossible to fix user-created buildings from before 17w47a, the bug addressed must be fixed before 1.13 is released.

Both custom and vanilla structures are affected by the lack of upgrade paths, ids that changed will not be corrected when the structure is loaded in, that is the bug, and that is Won’t Fix. Everybody, users and mojang, will need to update the structure files manually.

It would have been possible, even for user created structures because of upgrade paths, look into it yourself, not going to explain it.

I understand that putting in an upgrade path for structures is not going to happen but can we at least stop marking bug reports that are specifically pointing out that the Mojang structures don't load properly as duplicates of a this bug which has been marked as Won't Fix.

Having structures that are part of the game not load properly is a bug that will need to be fixed.

this will have to be fix at some point i'm sure that mojang have a world with all the pieces to the structures that aren't hard coded in just re-save them i'm slowly doing it to all of my custom structures and you think i want to be doing it NO but i am. even if they do 1 or a half a structure a major update like 1.14, 1.15 so on I and many others will most likely be happy with that.

Hey that's the problem I was having!