Persistent unit IDs

core/src/mindustry/io/versions/LegacySaveVersion2.java

@@ -0,0 +1,37 @@
+package mindustry.io.versions;
+
+import arc.func.*;
+import arc.util.io.*;
+import mindustry.gen.*;
+import mindustry.io.*;
+
+import java.io.*;
+
+/** This version did not read/write entity IDs to the save. */
+public class LegacySaveVersion2 extends SaveVersion{
+
+    public LegacySaveVersion2(int version){
+        super(version);
+    }
+
+    @Override
+    public void readWorldEntities(DataInput stream) throws IOException{
+        //entityMapping is null in older save versions, so use the default
+        Prov[] mapping = this.entityMapping == null ? EntityMapping.idMap : this.entityMapping;
+
+        int amount = stream.readInt();
+        for(int j = 0; j < amount; j++){
+            readChunk(stream, true, in -> {
+                int typeid = in.readUnsignedByte();
+                if(mapping[typeid] == null){
+                    in.skipBytes(lastRegionLength - 1);
+                    return;
+                }
+
+                Entityc entity = (Entityc)mapping[typeid].get();
+                entity.read(Reads.get(in));
+                entity.add();
+            });
+        }
+    }
+}