TrialSpawners lose SpawnData/SpawnPotentials if a BlockTransformer has been registered for the Structure placing it

[Lauriichan]

Expected behavior

TrialSpawners should not lose any data in any circumstances

Observed/Actual behavior

TrialSpawners lose the SpawnData/SpawnPotentials if a BlockTransformer has been registered for a structure placing it (vanilla structures affected: Trial chambers)

Steps/models to reproduce

1. Create/Install a plugin that registers a BlockTransformer to the trial chambers structure
2. Setup and start a server and search for a trial chamber
3. Once a trial chamber is found you will see that the trial spawners have no SpanData or SpawnPotentials

Plugin and Datapack List

The test plugin that can be found in the spigot issue linked below

Paper version

Any version after the hardfork and before the hardfork since this spigot PR: https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/pull-requests/1354/overview

Other

Please checkout this issue, it shows the bug in spigot and its fix to it as it was introduced upstream before the hardfork: https://hub.spigotmc.org/jira/browse/SPIGOT-8068

[Lulu13022002]

I can't see that PR but i can confirm this behavior which is already fixed in #12732

[Lauriichan]

I am unsure if this fixes the issue, one of the issues is that the copy constructor of some of the BloclStates is wrong which was also fixed on the mentioned PR. And the mentioned Paper PR which supposedly fixes the TrialSpawners still seems to have that flaw.
As long as an object is not immutable it should not be reassigned from one BlockState to another without actually copying it, otherwise you could modify one of the configs and it would affect all copies which is one of the reasons why this broke im the first place.
The rework might do something different which fixes the side effect but the main cause doesn't seem to be fixed.

EDIT: PRs on Spigot can only be viewed with an Account on the Spigot Hub that is unlocked for contribution but I think the commit can be viewed which u can find here: https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/commits/596f58154d57949f7420bd1dc79c8af76768f007#src/main/java/org/bukkit/craftbukkit/block/CraftTrialSpawner.java

[Lulu13022002]

Not really some change in this commit doesn't apply to paper, like the vault one, for the banner this seems just redundant to clone the list twice since Banner#getPatterns already clone the underlying list. The only relevant change is the sign loading but it's not the issue reported in this ticket nor the main cause (fixed in the mentioned PR now).

[Lauriichan]

Great, thank you!

However I noticed this part right here stayed the same, are these configs immutable?
If so this should be fine however if not then they should not be referencing the configs of the state that is being copied