Add cancellability to PlayerTrackEntityEvent (#8605)

patches/api/Player-Entity-Tracking-Events.patch

@@ -14,17 +14,21 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +import org.bukkit.entity.Entity;
 +import org.bukkit.entity.Player;
++import org.bukkit.event.Cancellable;
 +import org.bukkit.event.HandlerList;
 +import org.bukkit.event.player.PlayerEvent;
 +import org.jetbrains.annotations.NotNull;
 +
 +/**
 + * Is called when a {@link Player} tracks an {@link Entity}.
++ * <p>
++ * If cancelled entity is not shown to the player and interaction in both directions is not possible.
 + */
-+public class PlayerTrackEntityEvent extends PlayerEvent {
++public class PlayerTrackEntityEvent extends PlayerEvent implements Cancellable {
 +
 +    private static final HandlerList handlers = new HandlerList();
 +    private final Entity entity;
++    private boolean cancelled;
 +
 +    public PlayerTrackEntityEvent(@NotNull Player player, @NotNull Entity entity) {
 +        super(player);
@@ -51,6 +55,16 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +    public Entity getEntity() {
 +        return entity;
 +    }
++
++    @Override
++    public boolean isCancelled() {
++        return cancelled;
++    }
++
++    @Override
++    public void setCancelled(boolean cancel) {
++        this.cancelled = cancel;
++    }
 +}
 diff --git a/src/main/java/io/papermc/paper/event/player/PlayerUntrackEntityEvent.java b/src/main/java/io/papermc/paper/event/player/PlayerUntrackEntityEvent.java
 new file mode 100644

patches/server/Player-Entity-Tracking-Events.patch

@@ -4,31 +4,26 @@ Date: Wed, 30 Mar 2022 18:16:52 +0200
 Subject: [PATCH] Player Entity Tracking Events
 
 
-diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
+diff --git a/src/main/java/net/minecraft/server/level/ChunkMap.java b/src/main/java/net/minecraft/server/level/ChunkMap.java
 index 0000000000000000000000000000000000000000..0000000000000000000000000000000000000000 100644
---- a/src/main/java/net/minecraft/world/entity/Entity.java
-+++ b/src/main/java/net/minecraft/world/entity/Entity.java
-@@ -0,0 +0,0 @@ public abstract class Entity implements Nameable, EntityAccess, CommandSource {
-         EnchantmentHelper.doPostDamageEffects(attacker, target);
-     }
+--- a/src/main/java/net/minecraft/server/level/ChunkMap.java
++++ b/src/main/java/net/minecraft/server/level/ChunkMap.java
+@@ -0,0 +0,0 @@ public class ChunkMap extends ChunkStorage implements ChunkHolder.PlayerProvider
+                 // CraftBukkit end
+                 if (flag) {
+                     if (this.seenBy.add(player.connection)) {
++                        // Paper start - entity tracking events
++                        if (io.papermc.paper.event.player.PlayerTrackEntityEvent.getHandlerList().getRegisteredListeners().length == 0 || new io.papermc.paper.event.player.PlayerTrackEntityEvent(player.getBukkitEntity(), this.entity.getBukkitEntity()).callEvent()) {
+                         this.serverEntity.addPairing(player);
++                        }
++                        // Paper end
+                     }
+                 } else if (this.seenBy.remove(player.connection)) {
++                    // Paper start - entity tracking events
++                    if (io.papermc.paper.event.player.PlayerUntrackEntityEvent.getHandlerList().getRegisteredListeners().length > 0) {
++                        new io.papermc.paper.event.player.PlayerUntrackEntityEvent(player.getBukkitEntity(), this.entity.getBukkitEntity()).callEvent();
++                    }
++                    // Paper end
+                     this.serverEntity.removePairing(player);
+                 }
  
--    public void startSeenByPlayer(ServerPlayer player) {}
-+    // Paper start
-+    public void startSeenByPlayer(ServerPlayer player) {
-+        if (io.papermc.paper.event.player.PlayerTrackEntityEvent.getHandlerList().getRegisteredListeners().length > 0) {
-+            new io.papermc.paper.event.player.PlayerTrackEntityEvent(player.getBukkitEntity(), this.getBukkitEntity()).callEvent();
-+        }
-+    }
-+    // Paper end
- 
--    public void stopSeenByPlayer(ServerPlayer player) {}
-+    // Paper start
-+    public void stopSeenByPlayer(ServerPlayer player) {
-+        if(io.papermc.paper.event.player.PlayerUntrackEntityEvent.getHandlerList().getRegisteredListeners().length > 0) {
-+            new io.papermc.paper.event.player.PlayerUntrackEntityEvent(player.getBukkitEntity(), this.getBukkitEntity()).callEvent();
-+        }
-+    }
-+    // Paper end
- 
-     public float rotate(Rotation rotation) {
-         float f = Mth.wrapDegrees(this.getYRot());