force entity dismount during teleportation

Entities must be dismounted before teleportation in order to avoid
multiple issues in the server with regards to teleportation, shamefully,
too many plugins rely on the events firing, which means that not firing
these events caues more issues than it solves;

In order to counteract this, Entity dismount/exit vehicle events have
been modified to supress cancellation (and has a method to allow plugins
to check if this has been set), noting that cancellation will be silently
surpressed given that plugins are not expecting this event to not be cancellable.

This is a far from ideal scenario, however: given the current state of this
event and other alternatives causing issues elsewhere, I believe that
this is going to be the best soultion all around.

Improvements/suggestions welcome!

paper-server/patches/sources/net/minecraft/server/level/ServerPlayer.java.patch

@@ -114,7 +114,7 @@
      @Nullable
      private Vec3 startingToFallPosition;
      @Nullable
-@@ -258,6 +293,30 @@
+@@ -258,7 +293,31 @@
      private final CommandSource commandSource;
      private int containerCounter;
      public boolean wonGame;
@@ -123,7 +123,7 @@
 +    public boolean queueHealthUpdatePacket;
 +    public net.minecraft.network.protocol.game.ClientboundSetHealthPacket queuedHealthUpdatePacket;
 +    // Paper end - cancellable death event
-+
+ 
 +    // CraftBukkit start
 +    public CraftPlayer.TransferCookieConnection transferCookieConnection;
 +    public String displayName;
@@ -142,9 +142,10 @@
 +    // CraftBukkit end
 +    public boolean isRealPlayer; // Paper
 +    public com.destroystokyo.paper.event.entity.PlayerNaturallySpawnCreaturesEvent playerNaturallySpawnedEvent; // Paper - PlayerNaturallySpawnCreaturesEvent
- 
++
      public ServerPlayer(MinecraftServer server, ServerLevel world, GameProfile profile, ClientInformation clientOptions) {
          super(world, world.getSharedSpawnPos(), world.getSharedSpawnAngle(), profile);
+         this.chatVisibility = ChatVisiblity.FULL;
 @@ -266,7 +325,7 @@
          this.canChatColor = true;
          this.lastActionTime = Util.getMillis();
@@ -379,10 +380,12 @@
                              Logger logger = ServerPlayer.LOGGER;
  
                              Objects.requireNonNull(logger);
-@@ -686,6 +835,29 @@
- 
-     }
+@@ -684,7 +833,30 @@
+             }
+         }
  
++    }
++
 +    // CraftBukkit start - World fallback code, either respawn location or global spawn
 +    public void spawnIn(Level world) {
 +        this.setLevel(world);
@@ -403,12 +406,11 @@
 +            this.setPos(position);
 +        }
 +        this.gameMode.setLevel((ServerLevel) world);
-+    }
+     }
 +    // CraftBukkit end
-+
+ 
      public void setExperiencePoints(int points) {
          float f = (float) this.getXpNeededForNextLevel();
-         float f1 = (f - 1.0F) / f;
 @@ -744,6 +916,11 @@
  
      @Override
@@ -524,7 +526,7 @@
 +        // SPIGOT-5071: manually add player loot tables (SPIGOT-5195 - ignores keepInventory rule)
 +        this.dropFromLootTable(this.serverLevel(), damageSource, this.lastHurtByPlayerTime > 0);
 +        this.dropCustomDeathLoot(this.serverLevel(), damageSource, flag);
-+
+ 
 +        loot.addAll(this.drops);
 +        this.drops.clear(); // SPIGOT-5188: make sure to clear
 +
@@ -548,7 +550,7 @@
 +        if (this.containerMenu != this.inventoryMenu) {
 +            this.closeContainer(org.bukkit.event.inventory.InventoryCloseEvent.Reason.DEATH); // Paper - Inventory close reason
 +        }
- 
++
 +        net.kyori.adventure.text.Component deathMessage = event.deathMessage() != null ? event.deathMessage() : net.kyori.adventure.text.Component.empty(); // Paper - Adventure
 +
 +        if (deathMessage != null && deathMessage != net.kyori.adventure.text.Component.empty() && flag) { // Paper - Adventure // TODO: allow plugins to override?
@@ -844,7 +846,7 @@
 +                // CraftBukkit end
                  return this;
              }
-+        }
+         }
 +    }
 +
 +    // CraftBukkit start
@@ -855,7 +857,7 @@
 +        Bukkit.getServer().getPluginManager().callEvent(event);
 +        if (event.isCancelled() || event.getTo() == null || event.getTo().getWorld() == null) {
 +            return null;
-         }
++        }
 +        return new CraftPortalEvent(event);
      }
 +    // CraftBukkit end
@@ -1430,7 +1432,24 @@
                  }
  
                  this.awardStat(Stats.DROP);
-@@ -2375,10 +2906,12 @@
+@@ -2275,9 +2806,15 @@
+ 
+     @Override
+     public void stopRiding() {
++        // Paper start - Force entity dismount during teleportation
++        this.stopRiding(false);
++    }
++    @Override
++    public void stopRiding(boolean suppressCancellation) {
++        // Paper end - Force entity dismount during teleportation
+         Entity entity = this.getVehicle();
+ 
+-        super.stopRiding();
++        super.stopRiding(suppressCancellation); // Paper - Force entity dismount during teleportation
+         if (entity instanceof LivingEntity entityliving) {
+             Iterator iterator = entityliving.getActiveEffects().iterator();
+ 
+@@ -2375,16 +2912,161 @@
          return TicketType.ENDER_PEARL.timeout();
      }
  
@@ -1446,10 +1465,11 @@
          }
  
          private static float calculateLookAtYaw(Vec3 respawnPos, BlockPos currentPos) {
-@@ -2387,4 +2920,147 @@
+             Vec3 vec3d1 = Vec3.atBottomCenterOf(currentPos).subtract(respawnPos).normalize();
+ 
              return (float) Mth.wrapDegrees(Mth.atan2(vec3d1.z, vec3d1.x) * 57.2957763671875D - 90.0D);
-         }
-     }
++        }
++    }
 +
 +    // CraftBukkit start - Add per-player time and weather.
 +    public long timeOffset = 0;
@@ -1462,8 +1482,8 @@
 +        } else {
 +            // Adds timeOffset to the beginning of this day.
 +            return this.level().getDayTime() - (this.level().getDayTime() % 24000) + this.timeOffset;
-+        }
-+    }
+         }
+     }
 +
 +    public WeatherType weather = null;
 +