Implement SupplyingExtent (#613)

worldedit-core/src/main/java/com/boydti/fawe/object/extent/SupplyingExtent.java

@@ -0,0 +1,24 @@
+package com.boydti.fawe.object.extent;
+
+import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.extent.PassthroughExtent;
+
+import java.util.function.Supplier;
+
+/**
+ * An extent that delegates actions to another extent that may change at any time.
+ */
+public class SupplyingExtent extends PassthroughExtent {
+
+    private final Supplier<Extent> extentSupplier;
+
+    public SupplyingExtent(Supplier<Extent> extentSupplier) {
+        super(extentSupplier.get());
+        this.extentSupplier = extentSupplier;
+    }
+
+    @Override
+    public Extent getExtent() {
+        return this.extentSupplier.get();
+    }
+}

worldedit-core/src/main/java/com/sk89q/worldedit/command/argument/FactoryConverter.java

@@ -19,6 +19,7 @@
 
 package com.sk89q.worldedit.command.argument;
 
+import com.boydti.fawe.object.extent.SupplyingExtent;
 import com.sk89q.worldedit.EmptyClipboardException;
 import com.sk89q.worldedit.LocalSession;
 import com.sk89q.worldedit.WorldEdit;
@@ -109,10 +110,10 @@ public class FactoryConverter<T> implements ArgumentConverter<T> {
             if (extent instanceof World) {
                 parserContext.setWorld((World) extent);
             }
-            parserContext.setExtent(new RequestExtent());
+            parserContext.setExtent(new SupplyingExtent(((Locatable) actor)::getExtent));
         } else if (session.hasWorldOverride()) {
             parserContext.setWorld(session.getWorldOverride());
-            parserContext.setExtent(new RequestExtent());
+            parserContext.setExtent(new SupplyingExtent(session::getWorldOverride));
         }
         parserContext.setSession(session);
         parserContext.setRestricted(true);