Made some masks use Extents rather than EditSessions.

src/main/java/com/sk89q/worldedit/masks/BlockMask.java

@@ -1,6 +1,7 @@
 package com.sk89q.worldedit.masks;
 
 import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.Extent;
 import com.sk89q.worldedit.Vector;
 import com.sk89q.worldedit.blocks.BaseBlock;
 
@@ -8,7 +9,7 @@ import java.util.Collection;
 import java.util.HashSet;
 import java.util.Set;
 
-public class BlockMask extends AbstractMask {
+public class BlockMask extends ExtentAwareMask {
 
     private final Set<BaseBlock> blocks;
 
@@ -42,7 +43,8 @@ public class BlockMask extends AbstractMask {
 
     @Override
     public boolean matches(EditSession editSession, Vector pos) {
-        BaseBlock block = editSession.getBlock(pos);
+        Extent extent = getExtent(editSession);
+        BaseBlock block = extent.getBlock(pos);
         return blocks.contains(block)
                 || blocks.contains(new BaseBlock(block.getType(), -1));
     }

src/main/java/com/sk89q/worldedit/masks/ExistingBlockMask.java

@@ -23,9 +23,9 @@ import com.sk89q.worldedit.EditSession;
 import com.sk89q.worldedit.Vector;
 import com.sk89q.worldedit.blocks.BlockID;
 
-public class ExistingBlockMask extends AbstractMask {
+public class ExistingBlockMask extends ExtentAwareMask {
     @Override
     public boolean matches(EditSession editSession, Vector pos) {
-        return editSession.getBlockType(pos) != BlockID.AIR;
+        return getExtent(editSession).getBlockType(pos) != BlockID.AIR;
     }
 }

src/main/java/com/sk89q/worldedit/masks/ExtentAwareMask.java

@@ -0,0 +1,71 @@
+/*
+ * 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 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.masks;
+
+import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.Extent;
+
+/**
+ * Extended by masks to make them potentially use an {@link Extent} rather than
+ * the {@link EditSession}.
+ * </p>
+ * At the moment, masks are coupled to {@link EditSession} when they should
+ * not be. However, because a change to {@link Mask} would cause massive breakage in
+ * the API, that change is deferred until further notice and this class exists as
+ * an opt-in mixin for adding support for {@link Extent}s.
+ */
+public abstract class ExtentAwareMask extends AbstractMask {
+
+    private Extent extent;
+
+    /**
+     * Get the extent that will be used for lookups.
+     *
+     * @return the extent, or null if the {@link EditSession} is to be used
+     */
+    public Extent getExtent() {
+        return extent;
+    }
+
+    /**
+     * Set the extent that will be used for lookups.
+     *
+     * @param extent the extent, or null if the {@link EditSession} is to be used
+     */
+    public void setExtent(Extent extent) {
+        this.extent = extent;
+    }
+
+    /**
+     * Get the extent to use for operations. Subclasses should call this method
+     * rather than access the passed {@link EditSession} directly.
+     *
+     * @param editSession the passed in {@link EditSession}
+     * @return an extent
+     */
+    protected Extent getExtent(EditSession editSession) {
+        if (extent != null) {
+            return extent;
+        } else {
+            return editSession;
+        }
+    }
+
+}

src/main/java/com/sk89q/worldedit/masks/FuzzyBlockMask.java

@@ -20,6 +20,7 @@
 package com.sk89q.worldedit.masks;
 
 import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.Extent;
 import com.sk89q.worldedit.Vector;
 import com.sk89q.worldedit.blocks.BaseBlock;
 
@@ -30,7 +31,7 @@ import java.util.Set;
  * Uses {@link BaseBlock#containsFuzzy(java.util.Collection, BaseBlock)} to
  * match blocks.
  */
-public class FuzzyBlockMask extends AbstractMask {
+public class FuzzyBlockMask extends ExtentAwareMask {
 
     private final Set<BaseBlock> filter;
 
@@ -58,7 +59,8 @@ public class FuzzyBlockMask extends AbstractMask {
 
     @Override
     public boolean matches(EditSession editSession, Vector pos) {
-        BaseBlock compare = new BaseBlock(editSession.getBlockType(pos), editSession.getBlockData(pos));
+        Extent extent = getExtent(editSession);
+        BaseBlock compare = new BaseBlock(extent.getBlockType(pos), extent.getBlockData(pos));
         return BaseBlock.containsFuzzy(filter, compare);
     }
 }

src/main/java/com/sk89q/worldedit/masks/SolidBlockMask.java

@@ -1,15 +1,17 @@
 package com.sk89q.worldedit.masks;
 
 import com.sk89q.worldedit.EditSession;
+import com.sk89q.worldedit.Extent;
 import com.sk89q.worldedit.Vector;
 import com.sk89q.worldedit.blocks.BlockType;
 
 /**
  * Works like {@link ExistingBlockMask}, except also dealing with non-solid non-air blocks the same way as with air.
  */
-public class SolidBlockMask extends AbstractMask {
+public class SolidBlockMask extends ExtentAwareMask {
     @Override
     public boolean matches(EditSession editSession, Vector pos) {
-        return !BlockType.canPassThrough(editSession.getBlockType(pos), editSession.getBlockData(pos));
+        Extent extent = getExtent(editSession);
+        return !BlockType.canPassThrough(extent.getBlockType(pos), extent.getBlockData(pos));
     }
 }

src/main/java/com/sk89q/worldedit/masks/UnderOverlayMask.java

@@ -21,17 +21,14 @@ package com.sk89q.worldedit.masks;
 
 import java.util.Set;
 
-import com.sk89q.worldedit.EditSession;
-import com.sk89q.worldedit.LocalPlayer;
-import com.sk89q.worldedit.LocalSession;
-import com.sk89q.worldedit.Vector;
+import com.sk89q.worldedit.*;
 import com.sk89q.worldedit.blocks.BaseBlock;
 
 /**
  *
  * @author 1337
  */
-public class UnderOverlayMask extends AbstractMask {
+public class UnderOverlayMask extends ExtentAwareMask {
     private final int yMod;
     private Mask mask;
 
@@ -68,6 +65,7 @@ public class UnderOverlayMask extends AbstractMask {
 
     @Override
     public boolean matches(EditSession editSession, Vector pos) {
-        return !mask.matches(editSession, pos) && mask.matches(editSession, pos.add(0, yMod, 0));
+        Extent extent = getExtent(editSession);
+        return !mask.matches(extent, pos) && mask.matches(extent, pos.add(0, yMod, 0));
     }
 }