The bug
When you hit an invulnerable guardian in survival, you will still get the thorns damage, even though you didn't even deal damage to it. Punching an invulnerable mob with armor enchanted with thorns won't do that.
How to reproduce
Summon an invulnerable guardian
/summon guardian ~ ~ ~ {Invulnerable:1b,NoAI:1b}
Switch to Survival mode
/gamemode survival
Punch it
Code analysis
Based on 1.11.2 decompiled using MCP 9.35 rc1
The method net.minecraft.entity.monster.EntityGuardian.attackEntityFrom(DamageSource, float)
attacks the damaging entity regardless of if the parent method successfully dealt damage.
Attachments
Comments


Does this issue still occur in snapshot 15w36d?

Ticket resolved as incomplete, because no answer in a reasonable amount of time (1+ year), if it still happens, please update the ticket.
Can confirm for MC 1.12.1.

affects 20w29a
Can confirm in 20w48a.
Can confirm in 20w51a.
Can confirm in 21w03a.
Can confirm in 21w05a.
Can confirm in 21w06a.
Can confirm in 21w07a. Video attached.
Can confirm in 21w11a.
Can confirm in 21w15a.
Can confirm in 1.17.
Can confirm in 1.17.1.
Can confirm in 1.18.2.
Can confirm in 1.19.1.
Can confirm in 1.19.2.

Can confirm in 1.19.4