Paper/patches/server/0451-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 017b0745753ea1907bad7022405db9a5a487d069..92fa6523f2bba105a74fff228e36e58666ed56ae 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);
             }