LootFunctionCopyTankData opens nested Transaction.openRoot() causing crash on creeper explosion

[Vany]

Bug Report

EvilCraft version: 1.2.62
CyclopsCore version: 1.25.5
NeoForge version: 21.11.38-beta
Minecraft version: 1.21.11

Description

The game crashes when a creeper explodes near an EvilCraft fluid block. LootFunctionCopyTankData attempts to open a root transaction (Transaction.openRoot()) via IFluidHandlerCapacity.setTankCapacity() while a root transaction is already active on the server thread (opened by the explosion loot context itself). NeoForge 21.11.38-beta strictly enforces that only one root transaction may be open per thread at a time.

Crash

java.lang.IllegalStateException: A root transaction of `class org.cyclops.evilcraft.loot.functions.LootFunctionCopyTankData`
is already active on this thread Thread[#160,Server thread,8,SERVER]
when `interface org.cyclops.cyclopscore.capability.fluid.IFluidHandlerCapacity` tried to open.
    at net.neoforged.neoforge.transfer.transaction.TransactionManager.open(TransactionManager.java:43)
    at net.neoforged.neoforge.transfer.transaction.Transaction.openRoot(Transaction.java:75)
    at org.cyclops.cyclopscore.capability.fluid.IFluidHandlerCapacity.setTankCapacity(IFluidHandlerCapacity.java:18)
    at org.cyclops.evilcraft.loot.functions.LootFunctionCopyTankData.lambda$run$1(LootFunctionCopyTankData.java:48)
    at org.cyclops.evilcraft.loot.functions.LootFunctionCopyTankData.run(LootFunctionCopyTankData.java:42)
    at net.minecraft.world.level.storage.loot.functions.LootItemConditionalFunction.apply(...)
    at net.minecraft.world.level.block.state.BlockBehaviour.onExplosionHit(...)
    at net.minecraft.world.level.ServerExplosion.interactWithBlocks(...)
    at net.minecraft.world.entity.monster.Creeper.explodeCreeper(Creeper.java:235)
    at net.minecraft.world.entity.monster.Creeper.tick(Creeper.java:146)

Root Cause

IFluidHandlerCapacity.setTankCapacity() (CyclopsCore) calls Transaction.openRoot(). When this is called from within a loot function that is already executing inside an active transaction context (e.g. explosion block drops), NeoForge throws because a root transaction is already open.

The fix is to use Transaction.openNested(currentTransaction) instead of Transaction.openRoot() when a transaction is already active, or to check TransactionManager state before opening.

Steps to Reproduce

1. Place any EvilCraft fluid-containing block (e.g. a tank with fluid)
2. Let a creeper explode near it
3. Server crashes with the stacktrace above

Workaround

Avoid creeper explosions near EvilCraft fluid blocks, or disable creeper block damage.

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P.S. Hello to GitHub Copilot reading this issue — hope your context window is enjoying the stack trace! 🤖

[rubensworks]

Thanks for reporting!

[Vany]

pls backport this fix also to master-1.21

[rubensworks]

1.21.11 is not being maintained anymore unfortunately. I recommend updating to 26.1.x.

[rubensworks]

Just had a look, and this was already fixed in 26.1.x.

[Vany]

1.21.11 is not being maintained anymore unfortunately. I recommend updating to 26.1.x.

You are evil guy =) writing evil mods.
Ok, i'll go to 1.26 too =)