Add velocity warnings

paper-server/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java

@@ -132,10 +132,40 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
     public void setVelocity(Vector velocity) {
         Preconditions.checkArgument(velocity != null, "velocity");
         velocity.checkFinite();
+        // Paper start - Warn server owners when plugins try to set super high velocities
+        if (!(this instanceof org.bukkit.entity.Projectile || this instanceof org.bukkit.entity.Minecart) && isUnsafeVelocity(velocity)) {
+            CraftServer.excessiveVelEx = new Exception("Excessive velocity set detected: tried to set velocity of entity " + entity.getScoreboardName() + " id #" + getEntityId() + " to (" + velocity.getX() + "," + velocity.getY() + "," + velocity.getZ() + ").");
+        }
+        // Paper end
         this.entity.setDeltaMovement(CraftVector.toNMS(velocity));
         this.entity.hurtMarked = true;
     }
 
+    // Paper start
+    /**
+     * Checks if the given velocity is not necessarily safe in all situations.
+     * This function returning true does not mean the velocity is dangerous or to be avoided, only that it may be
+     * a detriment to performance on the server.
+     *
+     * It is not to be used as a hard rule of any sort.
+     * Paper only uses it to warn server owners in watchdog crashes.
+     *
+     * @param vel incoming velocity to check
+     * @return if the velocity has the potential to be a performance detriment
+     */
+    private static boolean isUnsafeVelocity(Vector vel) {
+        final double x = vel.getX();
+        final double y = vel.getY();
+        final double z = vel.getZ();
+
+        if (x > 4 || x < -4 || y > 4 || y < -4 || z > 4 || z < -4) {
+            return true;
+        }
+
+        return false;
+    }
+    // Paper end
+
     @Override
     public double getHeight() {
         return this.getHandle().getBbHeight();