Hash collisions of item stacks causing wrong items to be stored

[kurrycat2004]

Describe the bug

AEItemStackRegistry#getRegisteredStack(ItemStack) only compares the hash of the input stack, without comparing the actual item stacks, making it vulnerable to hash collisions. This causes new items put into a system to "transform" into the already existing item if it has the same hash.

To Reproduce

• make a simple ME system
• put a Protection 1 enchanted book in
• put a Fire Protection 2 enchanted book in
• system now contains 2 Protection 1 books

Expected behavior

ME System correctly stores one Protection 1 book and one Fire Protection 2 book

Additional context

javaw_JnTSTzqIUE.mp4

Environment

Tested with only AE2

• Minecraft Version: 1.12.2
• AE2 Version: v0.56.6
• Forge Version: 14.23.5.2847

[PukPukov]

Is this an issue in original AE?

[kurrycat2004]

from what i could see, no

[embeddedt]

This appears to be a regression from 0.56.6; downgrading to 0.56.5 fixes it. Most likely this commit: 724f3ba

[Exaxxion]

For what it's worth, 0.56.6 has known issues and I was advised months ago not to update to it because of that.

[ghzdude]

this is concerning for CEu, since it uses the same kind of hash strategy

[IntegerLimit]

If CEu does, wouldn't it use a normal map, and not a weak map? From what I see in 724f3ba, I believe AE2 is using a weak map, which... doesn't compare equality, just hash, right?

At least, that is what I believe is happening, as normal maps check both hash and the equals function.

[ghzdude]

CEu uses this in OpenCustomHashMaps (from fastutil), i'm not sure if those use both hash and identity equals.

[IntegerLimit]

Yes, that should also check identity equals. AE2 seems to use this: 724f3ba, a 'Weak Values' Map from Google. Not sure if it is what I thought.