Paper/patches/server/0546-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 446ba28a38a597bc8c99e31087e5c90eb37f8335..44aecc47d94481cb6286a60fc2bb720e3486bcc2 100644
--- a/src/main/java/net/minecraft/world/item/PotionItem.java
+++ b/src/main/java/net/minecraft/world/item/PotionItem.java
@@ -53,6 +53,7 @@ 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();
@@ -61,7 +62,7 @@ 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
                 }
@@ -75,7 +76,18 @@ 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);
             }