Mob spawner block_entity_data does not copy SpawnData data to missing SpawnPotentials

Confirmed, but probably invalid because mob spawners are not supposed to be available in item form (MC-80597).

redstonehelper, mob spawners as item are commonly used in servers, so disabling it would be bad for them. The bug you linked to is no longer counting mob spawner.
This bug is not invalid and in my opinion should be fixed.=]

redstonehelper: You could argue that the entire BlockEntityTag is invalid with that argument.

Yes, I could have.

Confirmed for 1.9-pre2

Confirmed fixed; BlockEntityTag now corresponds with behavior of /setblock (filling in SpawnPotentials automatically).

Issue has resurfaced at some point between 16w32a and 1.11.

I've been messing with the latest snapshot (time of writing, so 17w17b) and noticed that this is still a problem. Was about to report when I found this issue. It's especially annoying for servers because using spawners is a lot less taxing than having to mess around with command blocks. Even better: spawners help to keep the game feel more natural.

I seem to be having this problem in 1.12 and 1.12.2 as well.

Confirmed for 1.13..

fix this the api was suppose to make it so you don't have to specify spawn potentials yet you have to here. confirmed for 1.13.1 pre 1

This problem has been resolved as far as I can tell.

If you place a spawner then it will default to spawning pigs. If you then set SpawnData as per example from the op:

/data merge block x y z {SpawnData:{id:"minecraft:zombie"}}

then it will change into a zombie spawner, spawn one (or more) zombies and then reset back to pigs. This is intended behavior because SpawnPotentials:[] (which hasn't changed) gets copied onto SpawnData. And 'potentials' was still set to pigs.

But if we use this command instead then the results will heavily change:

/data merge block x y z {SpawnPotentials:[{Entity:{id:"minecraft:zombie"},Weight:1}]}

First several pigs will spawn (which is intended because they were still specified in SpawnData) but after that the spawner will change into a zombie spawner and it will remain spawning zombies.

The same thing applies if you give yourself a spawner and only set SpawnPotentials: first it will spawn pigs, but then it will start spawning whatever entity you defined. This is fully as intended because SpawnData was never set (and thus is set to default).

Which makes me convinced that this bug has been resolved. I've never been able to use customized mob spawners in 1.12.2 but I can in 1.13.1

@unknown, the point is not to modify the data of an already placed spawner, but when placing a custom spawner the current SpawnData of the item should be copied into the (yet empty) SpawnPotentials of the yet placed block.

basically if it's a mob spawner they and don't have the tag on the itemstack they need to set it virtually before merging the nbt. Create a WeightedSpawnEntity(1,spawndataTag).toCompoundTag() and put it inside of a tag list. from there set that tag as spawnpotentials. When merging any additional data should get overridden by the 2d tag compound

Remains an issue as of 09Oct18.

jredfox, sounds like you were explaining a work-around, but I don't follow. By tag list you referring to as an example minecraft/tags/blocks/example.json? Can you reply again in more detail? Would be much appreciated 😃

It's not a work around any data that could get merged via TileEntity nbt's tags that would also have to get synced over has to be applied. In this case spawnpotentials should be deleted before placement. 

19w13a affected

1.14 and 1.14.1 are also affected

Edit: the bug as reported doesn't affect 1.14+ but unless you are in creative or are op on a server a custom spawner will always become a pig spawner.

It would be nice if this was changed.

I will post a feature request, because imo if a player has a way to get a custom spawner, then they should be able to place it.

I’m sorry to say, Valkon, but that’s never going to happen due to security exploits.

Players can easily save custom spawners that can spawn thousands of mobs a minute, or even command blocks, in their toolbars.

Then, with your feature request, they could place said spawners and cause massive destruction in another player’s server without OP.

TL;DR: No OP custom spawners are dangerous. Very dangerous.

CreeperMagnet, how is what you say possible? I don't get it.

If a player isn't op, then how do they get a spawner unless a server intentionally adds a method to give them one?

And if they do get one, how do they make it spawn thousands of mobs a minute unless they're given a spawner with higher rates? With default rates you'd need 50+ spawners to get even close to 1000 mobs per minute right?

It seems to me that even if non-op spawner placing was possible, it's still totally up to the server owners what they allow players to get their hands on - as it should be.

And if there are security exploits that allow non-op players to modify spawners to cause massive destruction, then those are bugs that should be fixed properly.

Players without OP can use creative mode’s saved toolbars. That is working as intended, and it will always be that way.

However, saved toolbars can be saved in any other world where the player has OP and can obtain spawners with modified NBT using /give—with modified spawnlimits, and delays so that it can spawn tickly, without a limit.

Then, if they were able to place these without OP, in any OTHER server, it would cause issues.

Being able to load toolbars without OP isn’t going to change. That’s a major purpose of toolbars, to be able to transfer items between worlds. However, the downside of this is non-OP players not being able to place custom spawners.

Would you rather be able to place some random spawners, or be able to keep your block palettes throughout worlds?

Ok I didn't know about that issue.
I don't play creative so have never really used a saved toolbar.

But isn't that issue part of a bigger exploit problem with saved toolbars that should be fixed properly?

Perhaps by not loading items you can't get via the creative inventory, or that's black listed on the server?
It's obviously not that simple I guess.

Confirmed in 1.16. The first command no longer works; it should be:

/setblock ~ ~ ~ spawner{SpawnData:{id:zombie}}

Can confirm in 21w05b.