Add RequestExtent to be used when a delayed EditSession is needed.

For example, if you set a mask that takes an extent (many of them),
and then move to another world, the mask will test blocks in the old
world and return bad results.

worldedit-core/src/main/java/com/sk89q/worldedit/session/request/RequestExtent.java

@@ -0,0 +1,109 @@
+/*
+ * WorldEdit, a Minecraft world manipulation toolkit
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.session.request;
+
+import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.WorldEditException;
+import com.sk89q.worldedit.entity.BaseEntity;
+import com.sk89q.worldedit.entity.Entity;
+import com.sk89q.worldedit.extent.Extent;
+import com.sk89q.worldedit.function.operation.Operation;
+import com.sk89q.worldedit.math.BlockVector2;
+import com.sk89q.worldedit.math.BlockVector3;
+import com.sk89q.worldedit.regions.Region;
+import com.sk89q.worldedit.util.Location;
+import com.sk89q.worldedit.world.biome.BiomeType;
+import com.sk89q.worldedit.world.block.BaseBlock;
+import com.sk89q.worldedit.world.block.BlockState;
+import com.sk89q.worldedit.world.block.BlockStateHolder;
+
+import javax.annotation.Nullable;
+import java.util.List;
+
+public class RequestExtent implements Extent {
+
+    private EditSession extent;
+
+    protected Extent getExtent() {
+        if (extent == null) {
+            extent = Request.request().getEditSession();
+        }
+        return extent;
+    }
+
+    @Override
+    public BlockVector3 getMinimumPoint() {
+        return getExtent().getMinimumPoint();
+    }
+
+    @Override
+    public BlockVector3 getMaximumPoint() {
+        return getExtent().getMaximumPoint();
+    }
+
+    @Override
+    public List<? extends Entity> getEntities(Region region) {
+        return getExtent().getEntities(region);
+    }
+
+    @Override
+    public List<? extends Entity> getEntities() {
+        return getExtent().getEntities();
+    }
+
+    @Override
+    @Nullable
+    public Entity createEntity(Location location, BaseEntity entity) {
+        return getExtent().createEntity(location, entity);
+    }
+
+    @Override
+    public BlockState getBlock(BlockVector3 position) {
+        return getExtent().getBlock(position);
+    }
+
+    @Override
+    public BaseBlock getFullBlock(BlockVector3 position) {
+        return getExtent().getFullBlock(position);
+    }
+
+    @Override
+    public BiomeType getBiome(BlockVector2 position) {
+        return getExtent().getBiome(position);
+    }
+
+    @Override
+    public <T extends BlockStateHolder<T>> boolean setBlock(BlockVector3 position, T block) throws WorldEditException {
+        return getExtent().setBlock(position, block);
+    }
+
+    @Override
+    public boolean setBiome(BlockVector2 position, BiomeType biome) {
+        return getExtent().setBiome(position, biome);
+    }
+
+    @Override
+    @Nullable
+    public Operation commit() {
+        Operation commit = getExtent().commit();
+        extent = null;
+        return commit;
+    }
+}