fix to handle invalid structures with invalid boxes.

docs/scarpet/api/BlocksAndWorldAccess.md

@@ -685,7 +685,7 @@ making it preferred for scoping ungenerated terrain, but it takes some compute r
 Unlike `'structure'` this will return a tentative structure location. Random factors in world generation may prevent
 the actual structure from forming.
   
-If structure is specified, it will return `null` if a chunk is not eligible, `true` if the structure should appear, or 
+If structure is specified, it will return `null` if a chunk is not eligible or invalid, `true` if the structure should appear, or 
 a map with two values: `'box'` for a pair of coordinates indicating bounding box of the structure, and `'pieces'` for 
 list of elements of the structure (as a tuple), with its name, direction, and box coordinates of the piece.
 
@@ -702,7 +702,7 @@ the first case it returns a map of structures at a given position, keyed by stru
 the bounding box of the structure - a pair of two 3-value coords (see examples). When called with an extra structure 
 name, returns a map with two values, `'box'` for bounding box of the structure, and `'pieces'` for a list of 
 components for that structure, with their name, direction and two sets of coordinates 
-indicating the bounding box of the structure piece.
+indicating the bounding box of the structure piece. If structure is invalid, its data will be `null`.
 
 Requires a `Standard Structure` name (see above).
 

src/main/java/carpet/script/api/WorldAccess.java

@@ -1128,7 +1128,17 @@ public class WorldAccess {
             Map<Value, Value> ret = new HashMap<>();
             for(StructureFeature<?> str : StructureFeature.STRUCTURES.values())
             {
-                StructureStart start = FeatureGenerator.shouldStructureStartAt(world, pos, str, needSize);
+                StructureStart<?> start;
+                try
+                {
+                    start = FeatureGenerator.shouldStructureStartAt(world, pos, str, needSize);
+                }
+                catch (NullPointerException npe)
+                {
+                    CarpetSettings.LOG.error("Failed to detect structure: "+str.getName());
+                    start = null;
+                }
+
                 if (start == null) continue;
 
                 Value key = new StringValue(NBTSerializableValue.nameFromRegistryId(Registry.STRUCTURE_FEATURE.getId(str)));

src/main/java/carpet/script/value/ValueConversions.java

@@ -299,10 +299,19 @@ public class ValueConversions
     public static Value of(StructureStart<?> structure)
     {
         if (structure == null || structure == StructureStart.DEFAULT) return Value.NULL;
+        BlockBox boundingBox = structure.getBoundingBox();
+        if (boundingBox.maxX < boundingBox.minX || boundingBox.maxY < boundingBox.minY || boundingBox.maxZ < boundingBox.minZ) return Value.NULL;
+        Map<Value, Value> ret = new HashMap<>();
+        ret.put(new StringValue("box"), ListValue.of(
+                ListValue.fromTriple(boundingBox.minX, boundingBox.minY, boundingBox.minZ),
+                ListValue.fromTriple(boundingBox.maxX, boundingBox.maxY, boundingBox.maxZ)
+        ));
         List<Value> pieces = new ArrayList<>();
         for (StructurePiece piece : structure.getChildren())
         {
             BlockBox box = piece.getBoundingBox();
+            if (box.maxX >= box.minX && box.maxY >= box.minY && box.maxZ >= box.minZ)
+            {
                 pieces.add(ListValue.of(
                         new StringValue(NBTSerializableValue.nameFromRegistryId(Registry.STRUCTURE_PIECE.getId(piece.getType()))),
                         (piece.getFacing() == null) ? Value.NULL : new StringValue(piece.getFacing().getName()),
@@ -310,12 +319,7 @@ public class ValueConversions
                         ListValue.fromTriple(box.maxX, box.maxY, box.maxZ)
                 ));
             }
-        BlockBox boundingBox = structure.getBoundingBox();
+        }
-        Map<Value, Value> ret = new HashMap<>();
-        ret.put(new StringValue("box"), ListValue.of(
-                ListValue.fromTriple(boundingBox.minX, boundingBox.minY, boundingBox.minZ),
-                ListValue.fromTriple(boundingBox.maxX, boundingBox.maxY, boundingBox.maxZ)
-        ));
         ret.put(new StringValue("pieces"), ListValue.wrap(pieces));
         return MapValue.wrap(ret);
     }