Make FlowerPotBlock extensible and reusable for mods

- Change static lookup map to an instance variable
- Add an instance variable for the "empty pot" for the current block
- Keep one instance of the lookup map between the empty pot and all its full versions
- Convert everything to use delegates

src/test/java/net/minecraftforge/debug/block/FlowerPotTest.java

@@ -0,0 +1,59 @@
+/*
+ * Minecraft Forge
+ * Copyright (c) 2016-2019.
+ *
+ * This library 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 version 2.1
+ * of the License.
+ *
+ * This library 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 library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+
+package net.minecraftforge.debug.block;
+
+import net.minecraft.block.Block;
+import net.minecraft.block.Blocks;
+import net.minecraft.block.FlowerPotBlock;
+import net.minecraft.item.BlockItem;
+import net.minecraft.item.Item;
+import net.minecraftforge.event.RegistryEvent;
+import net.minecraftforge.eventbus.api.SubscribeEvent;
+import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.common.Mod.EventBusSubscriber.Bus;
+import net.minecraftforge.registries.ObjectHolder;
+
+@Mod(FlowerPotTest.MODID)
+@Mod.EventBusSubscriber(bus = Bus.MOD)
+public class FlowerPotTest
+{
+    static final String MODID = "flower_pot_test";
+    static final String BLOCK_ID = "test_flower_pot";
+
+    @ObjectHolder(BLOCK_ID)
+    public static FlowerPotBlock EMPTY_FLOWER_POT;
+
+    @ObjectHolder(BLOCK_ID)
+    public static FlowerPotBlock OAK_FLOWER_POT;
+
+    @SubscribeEvent
+    public static void registerBlocks(RegistryEvent.Register<Block> event)
+    {
+        FlowerPotBlock empty = new FlowerPotBlock(null, Blocks.AIR, Block.Properties.from(Blocks.FLOWER_POT));
+        event.getRegistry().register(empty.setRegistryName(BLOCK_ID));
+        event.getRegistry().register(new FlowerPotBlock(empty, Blocks.OAK_SAPLING, Block.Properties.from(empty)).setRegistryName(BLOCK_ID + "_oak"));
+    }
+
+    @SubscribeEvent
+    public static void registerItems(RegistryEvent.Register<Item> event)
+    {
+        event.getRegistry().register(new BlockItem(EMPTY_FLOWER_POT, new Item.Properties()).setRegistryName(MODID, BLOCK_ID));
+    }
+}

src/test/java/net/minecraftforge/debug/block/StickyBlockTest.java

@@ -27,10 +27,11 @@ import net.minecraft.item.Item;
 import net.minecraftforge.event.RegistryEvent;
 import net.minecraftforge.eventbus.api.SubscribeEvent;
 import net.minecraftforge.fml.common.Mod;
+import net.minecraftforge.fml.common.Mod.EventBusSubscriber.Bus;
 import net.minecraftforge.registries.ObjectHolder;
 
 @Mod(StickyBlockTest.MODID)
-@Mod.EventBusSubscriber
+@Mod.EventBusSubscriber(bus = Bus.MOD)
 public class StickyBlockTest
 {
     static final String MODID = "custom_slime_block_test";