Remove wall-time / unused skip tick protection (#11412)

Spigot still maintains some partial implementation of "tick skipping", a
practice in which the MinecraftServer.currentTick field is updated not
by an increment of one per actual tick, but instead set to
System.currentTimeMillis() / 50. This behaviour means that the tracked
tick may "skip" a tick value in case a previous tick took more than the
expected 50ms.

To compensate for this in important paths, spigot/craftbukkit
implements "wall-time". Instead of incrementing/decrementing ticks on
block entities/entities by one for each call to their tick() method,
they instead increment/decrement important values, like
an ItemEntity's age or pickupDelay, by the difference of
`currentTick - lastTick`, where `lastTick` is the value of
`currentTick` during the last tick() call.

These "fixes" however do not play nicely with minecraft's simulation
distance as entities/block entities implementing the above behaviour
would "catch up" their values when moving from a non-ticking chunk to a
ticking one as their `lastTick` value remains stuck on the last tick in
a ticking chunk and hence lead to a large "catch up" once ticked again.

Paper completely removes the "tick skipping" behaviour (See patch
"Further-improve-server-tick-loop"), making the above precautions
completely unnecessary, which also rids paper of the previous described
incompatibility with non-ticking chunks.

1 files changed, 72 insertions, 0 deletions

diff --git a/patches/server/0532-ItemStack-repair-check-API.patch b/patches/server/0532-ItemStack-repair-check-API.patch
new file mode 100644
index 0000000000..ab9ccec1cd
--- /dev/null
+++ b/patches/server/0532-ItemStack-repair-check-API.patch
@@ -0,0 +1,72 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jake Potrebic <[email protected]>
+Date: Sat, 15 May 2021 22:11:11 -0700
+Subject: [PATCH] ItemStack repair check API
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java b/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
+index f833fcead688180daf7039e09dce46fde924043c..07de1316b65e71ab0a372f1a51ae3bc6953d6530 100644
+--- a/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
++++ b/src/main/java/org/bukkit/craftbukkit/util/CraftMagicNumbers.java
+@@ -526,6 +526,14 @@ public final class CraftMagicNumbers implements UnsafeValues {
+     public int getProtocolVersion() {
+         return net.minecraft.SharedConstants.getCurrentVersion().getProtocolVersion();
+     }
++
++    @Override
++    public boolean isValidRepairItemStack(org.bukkit.inventory.ItemStack itemToBeRepaired, org.bukkit.inventory.ItemStack repairMaterial) {
++        if (!itemToBeRepaired.getType().isItem() || !repairMaterial.getType().isItem()) {
++            return false;
++        }
++        return CraftMagicNumbers.getItem(itemToBeRepaired.getType()).isValidRepairItem(CraftItemStack.asNMSCopy(itemToBeRepaired), CraftItemStack.asNMSCopy(repairMaterial));
++    }
+     // Paper end
+ 
+     @Override
+diff --git a/src/test/java/io/papermc/paper/util/ItemStackRepairCheckTest.java b/src/test/java/io/papermc/paper/util/ItemStackRepairCheckTest.java
+new file mode 100644
+index 0000000000000000000000000000000000000000..9f8abe2376f16aeffe4e9f90a2da04b7e3a55429
+--- /dev/null
++++ b/src/test/java/io/papermc/paper/util/ItemStackRepairCheckTest.java
+@@ -0,0 +1,41 @@
++package io.papermc.paper.util;
++
++import org.bukkit.Material;
++import org.bukkit.inventory.ItemStack;
++import org.bukkit.support.AbstractTestingBase;
++import org.junit.jupiter.api.Test;
++
++import static org.junit.jupiter.api.Assertions.assertFalse;
++import static org.junit.jupiter.api.Assertions.assertThrows;
++import static org.junit.jupiter.api.Assertions.assertTrue;
++
++public class ItemStackRepairCheckTest extends AbstractTestingBase {
++
++    @Test
++    public void testIsRepariableBy() {
++        ItemStack diamondPick = new ItemStack(Material.DIAMOND_PICKAXE);
++
++        assertTrue(diamondPick.isRepairableBy(new ItemStack(Material.DIAMOND)), "diamond pick isn't repairable by a diamond");
++    }
++
++    @Test
++    public void testCanRepair() {
++        ItemStack diamond = new ItemStack(Material.DIAMOND);
++
++        assertTrue(diamond.canRepair(new ItemStack(Material.DIAMOND_AXE)), "diamond can't repair a diamond axe");
++    }
++
++    @Test
++    public void testIsNotRepairableBy() {
++        ItemStack notDiamondPick = new ItemStack(Material.ACACIA_SAPLING);
++
++        assertFalse(notDiamondPick.isRepairableBy(new ItemStack(Material.DIAMOND)), "acacia sapling is repairable by a diamond");
++    }
++
++    @Test
++    public void testCanNotRepair() {
++        ItemStack diamond = new ItemStack(Material.DIAMOND);
++
++        assertFalse(diamond.canRepair(new ItemStack(Material.OAK_BUTTON)), "diamond can repair oak button");
++    }
++}