WIP unit tether component

core/src/mindustry/content/UnitTypes.java

@@ -76,7 +76,7 @@ public class UnitTypes{
     //special block unit type
     public static @EntityDef({Unitc.class, BlockUnitc.class}) UnitType block;
 
-    //special tethered (has payload capability, because it's necessary sometimes)
+    //special building tethered (has payload capability, because it's necessary sometimes)
     public static @EntityDef({Unitc.class, BuildingTetherc.class, Payloadc.class}) UnitType manifold, assemblyDrone;
 
     //tank

core/src/mindustry/entities/comp/UnitTetherComp.java

@@ -0,0 +1,39 @@
+package mindustry.entities.comp;
+
+import arc.util.*;
+import mindustry.annotations.Annotations.*;
+import mindustry.game.*;
+import mindustry.gen.*;
+import mindustry.type.*;
+
+/** A unit that depends on a units's existence; if that unit is removed, it despawns. */
+@Component
+abstract class UnitTetherComp implements Unitc{
+    @Import UnitType type;
+    @Import Team team;
+
+    //spawner unit cannot be read directly for technical reasons.
+    public transient @Nullable Unit spawner;
+    public int spawnerUnitId = -1;
+
+    @Override
+    public void afterRead(){
+        if(spawnerUnitId != -1) spawner = Groups.unit.getByID(spawnerUnitId);
+        spawnerUnitId = -1;
+    }
+
+    @Override
+    public void afterSync(){
+        if(spawnerUnitId != -1) spawner = Groups.unit.getByID(spawnerUnitId);
+        spawnerUnitId = -1;
+    }
+
+    @Override
+    public void update(){
+        if(spawner == null || !spawner.isValid() || spawner.team != team){
+            Call.unitDespawn(self());
+        }else{
+            spawnerUnitId = spawner.id;
+        }
+    }
+}