Paper/patches/server/0551-Fix-harming-potion-dupe.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: PepperCode1 <44146161+PepperCode1@users.noreply.github.com>
Date: Thu, 23 Jul 2020 14:25:07 -0700
Subject: [PATCH] Fix harming potion dupe

EntityLiving#applyInstantEffect() immediately kills the player and drops their inventory.
Before this patch, instant effects would be applied before the potion ItemStack is removed and replaced with a glass bottle. This caused the potion ItemStack to be dropped before it was supposed to be removed from the inventory. It also caused the glass bottle to be put into a dead player's inventory.
This patch makes it so that instant effects are applied after the potion ItemStack is removed, and the glass bottle is only put into the player's inventory if the player is not dead. Otherwise, the glass bottle is dropped on the ground.

diff --git a/src/main/java/net/minecraft/world/item/PotionItem.java b/src/main/java/net/minecraft/world/item/PotionItem.java
index 166f7483163a0cf62b000764d635ec2ee36a5036..4b5c9da0e858016c1a3afcb6eaa1ff4cbf47739e 100644
--- a/src/main/java/net/minecraft/world/item/PotionItem.java
+++ b/src/main/java/net/minecraft/world/item/PotionItem.java
@@ -41,6 +41,7 @@ public class PotionItem extends Item {
             CriteriaTriggers.CONSUME_ITEM.trigger((ServerPlayer) entityhuman, stack);
         }
 
+        List<MobEffectInstance> instantLater = new java.util.ArrayList<>(); // Paper - Fix harming potion dupe
         if (!world.isClientSide) {
             List<MobEffectInstance> list = PotionUtils.getMobEffects(stack);
             Iterator iterator = list.iterator();
@@ -49,7 +50,7 @@ public class PotionItem extends Item {
                 MobEffectInstance mobeffect = (MobEffectInstance) iterator.next();
 
                 if (mobeffect.getEffect().isInstantenous()) {
-                    mobeffect.getEffect().applyInstantenousEffect(entityhuman, entityhuman, user, mobeffect.getAmplifier(), 1.0D);
+                    instantLater.add(mobeffect); // Paper - Fix harming potion dupe
                 } else {
                     user.addEffect(new MobEffectInstance(mobeffect), org.bukkit.event.entity.EntityPotionEffectEvent.Cause.POTION_DRINK); // CraftBukkit
                 }
@@ -63,7 +64,18 @@ public class PotionItem extends Item {
             }
         }
 
+        // Paper start - Fix harming potion dupe
+        for (MobEffectInstance mobeffect : instantLater) {
+            mobeffect.getEffect().applyInstantenousEffect(entityhuman, entityhuman, user, mobeffect.getAmplifier(), 1.0D);
+        }
+        // Paper end
         if (entityhuman == null || !entityhuman.getAbilities().instabuild) {
+            // Paper start - Fix harming potion dupe
+            if (user.getHealth() <= 0 && !user.level.getGameRules().getBoolean(net.minecraft.world.level.GameRules.RULE_KEEPINVENTORY)) {
+                user.spawnAtLocation(new ItemStack(Items.GLASS_BOTTLE), 0);
+                return ItemStack.EMPTY;
+            }
+            // Paper end
             if (stack.isEmpty()) {
                 return new ItemStack(Items.GLASS_BOTTLE);
             }