PaperMC/paper-server/nms-patches/net/minecraft/server/commands/CommandTeleport.patch

--- a/net/minecraft/server/commands/CommandTeleport.java
+++ b/net/minecraft/server/commands/CommandTeleport.java
@@ -36,6 +36,12 @@
 import net.minecraft.world.phys.Vec2F;
 import net.minecraft.world.phys.Vec3D;
 
+// CraftBukkit start
+import org.bukkit.Location;
+import org.bukkit.craftbukkit.CraftWorld;
+import org.bukkit.event.entity.EntityTeleportEvent;
+// CraftBukkit end
+
 public class CommandTeleport {
 
     private static final SimpleCommandExceptionType INVALID_POSITION = new SimpleCommandExceptionType(new ChatMessage("commands.teleport.invalidPosition"));
@@ -160,14 +166,29 @@
                 }
 
                 if (worldserver == entity.level) {
-                    ((EntityPlayer) entity).connection.a(d0, d1, d2, f2, f3, set);
+                    ((EntityPlayer) entity).connection.a(d0, d1, d2, f2, f3, set, org.bukkit.event.player.PlayerTeleportEvent.TeleportCause.COMMAND); // CraftBukkit
                 } else {
-                    ((EntityPlayer) entity).a(worldserver, d0, d1, d2, f2, f3);
+                    ((EntityPlayer) entity).a(worldserver, d0, d1, d2, f2, f3, org.bukkit.event.player.PlayerTeleportEvent.TeleportCause.COMMAND); // CraftBukkit
                 }
 
                 entity.setHeadRotation(f2);
             } else {
                 float f4 = MathHelper.a(f3, -90.0F, 90.0F);
+                // CraftBukkit start - Teleport event
+                Location to = new Location(worldserver.getWorld(), d0, d1, d2, f2, f4);
+                EntityTeleportEvent event = new EntityTeleportEvent(entity.getBukkitEntity(), entity.getBukkitEntity().getLocation(), to);
+                worldserver.getCraftServer().getPluginManager().callEvent(event);
+                if (event.isCancelled()) {
+                    return;
+                }
+
+                d0 = to.getX();
+                d1 = to.getY();
+                d2 = to.getZ();
+                f2 = to.getYaw();
+                f4 = to.getPitch();
+                worldserver = ((CraftWorld) to.getWorld()).getHandle();
+                // CraftBukkit end
 
                 if (worldserver == entity.level) {
                     entity.setPositionRotation(d0, d1, d2, f2, f4);