Fixes and changes to forest/forestgen.

* Sync up implementations of the two commands.
* Fix generating trees in spots with replaceable blocks.
* Make message when you mistype tree-type arg more correct.

Fixes WORLDEDIT-3869.

worldedit-core/src/main/java/com/sk89q/worldedit/EditSession.java

@@ -44,6 +44,7 @@ import com.sk89q.worldedit.function.block.BlockDistributionCounter;
 import com.sk89q.worldedit.function.block.BlockReplace;
 import com.sk89q.worldedit.function.block.Counter;
 import com.sk89q.worldedit.function.block.Naturalizer;
+import com.sk89q.worldedit.function.generator.ForestGenerator;
 import com.sk89q.worldedit.function.generator.GardenPatchGenerator;
 import com.sk89q.worldedit.function.mask.BlockMask;
 import com.sk89q.worldedit.function.mask.BlockStateMask;
@@ -1832,38 +1833,25 @@ public class EditSession implements Extent, AutoCloseable {
      * @throws MaxChangedBlocksException thrown if too many blocks are changed
      */
     public int makeForest(BlockVector3 basePosition, int size, double density, TreeGenerator.TreeType treeType) throws MaxChangedBlocksException {
-        int affected = 0;
-
-        for (int x = basePosition.getBlockX() - size; x <= basePosition.getBlockX()
-                + size; ++x) {
-            for (int z = basePosition.getBlockZ() - size; z <= basePosition.getBlockZ()
-                    + size; ++z) {
-                // Don't want to be in the ground
-                if (!getBlock(BlockVector3.at(x, basePosition.getBlockY(), z)).getBlockType().getMaterial().isAir()) {
-                    continue;
-                }
-                // The gods don't want a tree here
-                if (Math.random() >= density) {
-                    continue;
-                } // def 0.05
-
-                for (int y = basePosition.getBlockY(); y >= basePosition.getBlockY() - 10; --y) {
-                    // Check if we hit the ground
-                    BlockType t = getBlock(BlockVector3.at(x, y, z)).getBlockType();
-                    if (t == BlockTypes.GRASS_BLOCK || t == BlockTypes.DIRT) {
-                        treeType.generate(this, BlockVector3.at(x, y + 1, z));
-                        ++affected;
-                        break;
-                    } else if (t == BlockTypes.SNOW) {
-                        setBlock(BlockVector3.at(x, y, z), BlockTypes.AIR.getDefaultState());
-                    } else if (!t.getMaterial().isAir()) { // Trees won't grow on this!
-                        break;
-                    }
-                }
-            }
+        return makeForest(CuboidRegion.fromCenter(basePosition, size), density, treeType);
     }
 
-        return affected;
+    /**
+     * Makes a forest.
+     *
+     * @param region the region to generate trees in
+     * @param density between 0 and 1, inclusive
+     * @param treeType the tree type
+     * @return number of trees created
+     * @throws MaxChangedBlocksException thrown if too many blocks are changed
+     */
+    public int makeForest(Region region, double density, TreeGenerator.TreeType treeType) throws MaxChangedBlocksException {
+        ForestGenerator generator = new ForestGenerator(this, treeType);
+        GroundFunction ground = new GroundFunction(new ExistingBlockMask(this), generator);
+        LayerVisitor visitor = new LayerVisitor(asFlatRegion(region), minimumBlockY(region), maximumBlockY(region), ground);
+        visitor.setMask(new NoiseFilter2D(new RandomNoise(), density));
+        Operations.completeLegacy(visitor);
+        return ground.getAffected();
     }
 
     /**

worldedit-core/src/main/java/com/sk89q/worldedit/command/GenerationCommands.java

@@ -197,7 +197,8 @@ public class GenerationCommands {
     )
     @CommandPermissions("worldedit.generation.forest")
     @Logging(POSITION)
-    public void forestGen(Player player, LocalSession session, EditSession editSession, @Optional("10") int size, @Optional("tree") TreeType type, @Optional("5") double density) throws WorldEditException {
+    public void forestGen(Player player, LocalSession session, EditSession editSession, @Optional("10") int size,
+                          @Optional("tree") TreeType type, @Optional("5") @Range(min = 0, max = 100) double density) throws WorldEditException {
         density = density / 100;
         int affected = editSession.makeForest(session.getPlacementPosition(player), size, density, type);
         player.print(affected + " trees created.");

worldedit-core/src/main/java/com/sk89q/worldedit/command/RegionCommands.java

@@ -445,14 +445,8 @@ public class RegionCommands {
     @Logging(REGION)
     public void forest(Player player, EditSession editSession, @Selection Region region, @Optional("tree") TreeType type,
                        @Optional("5") @Range(min = 0, max = 100) double density) throws WorldEditException {
-        density = density / 100;
-        ForestGenerator generator = new ForestGenerator(editSession, type);
-        GroundFunction ground = new GroundFunction(new ExistingBlockMask(editSession), generator);
-        LayerVisitor visitor = new LayerVisitor(asFlatRegion(region), minimumBlockY(region), maximumBlockY(region), ground);
-        visitor.setMask(new NoiseFilter2D(new RandomNoise(), density));
-        Operations.completeLegacy(visitor);
-
-        player.print(ground.getAffected() + " trees created.");
+        int affected = editSession.makeForest(region, density / 100, type);
+        player.print(affected + " trees created.");
     }
 
     @Command(

worldedit-core/src/main/java/com/sk89q/worldedit/function/generator/ForestGenerator.java

@@ -54,15 +54,19 @@ public class ForestGenerator implements RegionFunction {
         BlockType t = block.getBlockType();
 
         if (t == BlockTypes.GRASS_BLOCK || t == BlockTypes.DIRT) {
-            treeType.generate(editSession, position.add(0, 1, 0));
-            return true;
-        } else if (t == BlockTypes.GRASS || t == BlockTypes.DEAD_BUSH || t == BlockTypes.POPPY || t == BlockTypes.DANDELION) { // TODO: This list needs to be moved
+            return treeType.generate(editSession, position.add(0, 1, 0));
+        } else if (t.getMaterial().isReplacedDuringPlacement()) {
+            // since the implementation's tree generators generally don't generate in non-air spots,
+            // we trick editsession history here in the first call
             editSession.setBlock(position, BlockTypes.AIR.getDefaultState());
-            treeType.generate(editSession, position);
-            return true;
-        } else if (t == BlockTypes.SNOW) {
-            editSession.setBlock(position, BlockTypes.AIR.getDefaultState());
-            return false;
+            // and then trick the generator here by directly setting into the world
+            editSession.getWorld().setBlock(position, BlockTypes.AIR.getDefaultState());
+            // so that now the generator can generate the tree
+            boolean success = treeType.generate(editSession, position);
+            if (!success) {
+                editSession.setBlock(position, block); // restore on failure
+            }
+            return success;
         } else { // Trees won't grow on this!
             return false;
         }

worldedit-core/src/main/java/com/sk89q/worldedit/internal/command/WorldEditBinding.java

@@ -52,6 +52,7 @@ import com.sk89q.worldedit.world.block.BaseBlock;
 import com.sk89q.worldedit.world.block.BlockState;
 import com.sk89q.worldedit.world.block.BlockStateHolder;
 import com.sk89q.worldedit.world.registry.BiomeRegistry;
+import sun.reflect.generics.tree.Tree;
 
 import java.util.Arrays;
 import java.util.Collection;
@@ -290,7 +291,8 @@ public class WorldEditBinding extends BindingHelper {
                 return type;
             } else {
                 throw new ParameterException(
-                        String.format("Can't recognize tree type '%s' -- choose from: %s", input, Arrays.toString(TreeType.values())));
+                        String.format("Can't recognize tree type '%s' -- choose from: %s", input,
+                                TreeType.getPrimaryAliases()));
             }
         } else {
             return TreeType.TREE;