Paper/patches/server/0469-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 de0b68b128e6ffbd31aebb4361e4859d495f89b5..042a9cf9c15fd30bc30e03d0e0311c70e40e6950 100644
--- a/src/main/java/net/minecraft/world/item/PotionItem.java
+++ b/src/main/java/net/minecraft/world/item/PotionItem.java
@@ -55,12 +55,13 @@ public class PotionItem extends Item {
             CriteriaTriggers.CONSUME_ITEM.trigger((ServerPlayer) entityhuman, stack);
         }
 
+        List<net.minecraft.world.effect.MobEffectInstance> instantLater = new java.util.ArrayList<>(); // Paper - Fix harming potion dupe
         if (!world.isClientSide) {
             PotionContents potioncontents = (PotionContents) stack.getOrDefault(DataComponents.POTION_CONTENTS, PotionContents.EMPTY);
 
             potioncontents.forEachEffect((mobeffect) -> {
                 if (((MobEffect) mobeffect.getEffect().value()).isInstantenous()) {
-                    ((MobEffect) mobeffect.getEffect().value()).applyInstantenousEffect(entityhuman, entityhuman, user, mobeffect.getAmplifier(), 1.0D);
+                    instantLater.add(mobeffect); // Paper
                 } else {
                     user.addEffect(mobeffect, org.bukkit.event.entity.EntityPotionEffectEvent.Cause.POTION_DRINK); // CraftBukkit
                 }
@@ -73,7 +74,18 @@ public class PotionItem extends Item {
             stack.consume(1, entityhuman);
         }
 
+        // Paper start - Fix harming potion dupe
+        for (net.minecraft.world.effect.MobEffectInstance mobeffect : instantLater) {
+            mobeffect.getEffect().value().applyInstantenousEffect(entityhuman, entityhuman, user, mobeffect.getAmplifier(), 1.0D);
+        }
+        // Paper end - Fix harming potion dupe
         if (entityhuman == null || !entityhuman.hasInfiniteMaterials()) {
+            // 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);
             }