[MC-41893] Breaking a minecart with command block in creative drops a minecart after reloading the world

How to reproduce

Place a minecart with command block
Leave and reopen the world
Destroy it in creative mode using your hand, a sword / tool or an arrow
→ The minecart with command block drops a (regular) minecart (item) named "@", whereas an empty / normal minecart would’ve dropped nothing after these steps. Also if you don’t leave and reopen the world first, the minecart with command blocks drops nothing either.

Code analysis

The following is based on decompiled version of Minecraft 1.8 using MCP. All method and class names are the names used in the decompiled version.

The reason why this happens is that the public void writeDataToNBT(NBTTagCompound p_145758_1_) method of the net.minecraft.command.server.CommandBlockLogic class always saves the CustomName in the NBT data. As this only happens when you unload the minecart or reopen the world a MinecartCommandBlock that is summoned and directly destroyed does not cause this. Instead the method should only save the CustomName if it is not "@".

/**
 * Stores data to NBT format.
 */
public void writeDataToNBT(NBTTagCompound p_145758_1_)
{
    p_145758_1_.setString("Command", this.commandStored);
    p_145758_1_.setInteger("SuccessCount", this.successCount);
    
    // Replaced this
    //p_145758_1_.setString("CustomName", this.customName);
    if (!this.customName.equals("@")) {
        p_145758_1_.setString("CustomName", this.customName);    
    }
    
    p_145758_1_.setBoolean("TrackOutput", this.trackOutput);

    if (this.lastOutput != null && this.trackOutput)
    {
        p_145758_1_.setString("LastOutput", IChatComponent.Serializer.componentToJson(this.lastOutput));
    }

    this.field_175575_g.func_179670_b(p_145758_1_);
}

Linked issues

Attachments

Comments 23

galaxy_2alex 2013-12-09T13:01:37Z

Confirmed

marcono1234 2015-08-23T16:09:42Z

Confirmed for

15w34d
15w35b

Incorrect duplicate link
This report is about unnamed MinecartCommandBlocks

[Mod] redstonehelper 2015-08-25T20:12:35Z

MinecartCommandBlocks are actually named.

marcono1234 2016-02-17T20:53:08Z

Confirmed for

1.9-pre1

@unknown this is a bug that only occurs when you reload the world

marcono1234 2016-02-17T21:14:30Z

Please link to this comment in the description

The following is based on decompiled version of Minecraft 1.8 using MCP. All method and class names are the names used in the decompiled version.

/**
 * Stores data to NBT format.
 */
public void writeDataToNBT(NBTTagCompound p_145758_1_)
{
    p_145758_1_.setString("Command", this.commandStored);
    p_145758_1_.setInteger("SuccessCount", this.successCount);
    
    // Replaced this
    //p_145758_1_.setString("CustomName", this.customName);
    if (!this.customName.equals("@")) {
        p_145758_1_.setString("CustomName", this.customName);    
    }
    
    p_145758_1_.setBoolean("TrackOutput", this.trackOutput);

    if (this.lastOutput != null && this.trackOutput)
    {
        p_145758_1_.setString("LastOutput", IChatComponent.Serializer.componentToJson(this.lastOutput));
    }

    this.field_175575_g.func_179670_b(p_145758_1_);
}

13 more comments

[Mod] redstonehelper 2016-02-17T21:25:28Z

So how is this not a duplicate of MC-10366?

marcono1234 2016-02-17T21:54:51Z

This one here is about the fact that when a MinecartCommandBlock gets saved the default CustomName is always saved, even if it is the default one which causes it to always drop the Minecart.
This bug here also happens in survival mode.

[Mod] redstonehelper 2016-02-17T22:59:37Z

I don't see anything wrong with saving the default CustomName.

marcono1234 2016-02-18T19:54:19Z

Saving the default name as CustomName causes this problem, that breaking the Minecart if its NBT data was not saved already does not drop anything, however once its NBT data was saved it drops a renamed minecart.

Anyways it is definitely not a duplicate of MC-10366 because the bug described in this report happen in Survival mode as well

[Mod] redstonehelper 2016-02-18T21:58:38Z

I think we're talking over each other. I'm saying "Minecarts even save the default custom name (a preset, if you will)" is not a bug. The fact that command block minecarts drop when destroyed after reloading is caused by MC-10366. When MC-10366 is fixed, minecart command blocks will stop dropping when destroyed after reloading.

that breaking the Minecart if its NBT data was not saved already does not drop anything

I do not consider this a problem - minecart command blocks, just like command blocks, are not meant for survival, so they don't drop in survival. They don't drop in creative because minecarts in general don't drop in creative.

I agree, the fact that renamed command block minecarts drop themselves in survival is a bug. Please create a separate ticket for that.

marcono1234 2016-02-19T13:17:28Z

I agree, the fact that renamed command block minecarts drop themselves in survival is a bug. Please create a separate ticket for that.

As they only drop a minecart item, but no command block, I am not sure if this is really a bug, but it could be, see MC-11765.

However as long as it is not confirmed to be a bug this report here has to stay open.
Like I said these are two different bugs and many of the optional tags like NoAI are not saved if they contain the default value.

Even if it is confirmed to be bug, this report is still no duplicate of MC-10366.

Edit: It could be solved indeed better by only saving the custom name if one is set and having a constant which stores the default custom name.

marcono1234 2016-02-19T13:20:08Z

MC-48862, MC-33178 are duplicates of this report instead of MC-10366.

[Mod] redstonehelper 2016-02-19T13:57:21Z

Reopened. I completely missed that they drop regular minecarts instead of command block minecarts.

marcono1234 2016-02-19T14:25:50Z

Thank you 🙂

That is however intended, see MC-54899

Please update the link accordingly as it still says "duplicates" MC-10366 instead of "relates to"

JUE13 2017-05-24T03:52:22Z

Confirmed for 1.12-pre5

pokechu22 2017-08-02T18:37:42Z

In the code analysis you write if (this.customName != "@"); this won't work and should be if (!this.customName.equals("@")).

[Mod] markderickson 2020-06-29T16:38:26Z

Hi there!

Can confirm in 1.16.1.

pulpetti 2020-07-06T18:34:46Z

Affects 1.16

Marty McFly 2021-05-28T13:21:58Z

Affects 1.17 Pre-release 1

Marty McFly 2021-06-09T12:44:54Z

Affects 1.17

Avoma 2022-08-07T12:51:42Z

Can confirm in 1.19.2.

PurPur134 2023-12-11T02:03:05Z

Destroying one that is renamed without relogging drops a regular minecart, with the same name. Though, placing it down and relogging still drops a minecart named "@".

iliketra1ns 2024-10-13T11:01:11Z

Cannot reproduce in 1.21.2 Pre-Release 3
Tested with experimental minecart improvements datapack enabled.

Breaking a minecart with command block in creative drops a minecart after reloading the world

How to reproduce

Code analysis

Linked issues

clones 1

is duplicated by 5

relates to 1

testing discovered 1

Attachments

Comments 23