Paper/patches/server/0476-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 bb19a00c24e92058e05076b2ca0278dcae1890ae..5c62741e3a3854a7f674bfec49758f837f3bb9a0 100644
--- a/src/main/java/net/minecraft/world/item/PotionItem.java
+++ b/src/main/java/net/minecraft/world/item/PotionItem.java
@@ -50,6 +50,7 @@ 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();
@@ -58,7 +59,7 @@ 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
                 }
@@ -72,7 +73,18 @@ 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 - Fix harming potion dupe
         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 - Fix harming potion dupe
             if (stack.isEmpty()) {
                 return new ItemStack(Items.GLASS_BOTTLE);
             }