Fix a vanilla bug with the blockstate ID map not being properly symmetric with respect to block.getStateFromMeta - closes #3012 properly but probably has a random MCJIRA ticket somewhere too.

patches/minecraft/net/minecraft/block/Block.java.patch

@@ -1337,3 +1337,16 @@
      public static void func_149671_p()
      {
          func_176215_a(0, field_176230_a, (new BlockAir()).func_149663_c("air"));
+@@ -1169,11 +2323,7 @@
+             }
+             else
+             {
+-                for (IBlockState iblockstate : block16.func_176194_O().func_177619_a())
+-                {
+-                    int k = field_149771_c.func_148757_b(block16) << 4 | block16.func_176201_c(iblockstate);
+-                    field_176229_d.func_148746_a(iblockstate, k);
+-                }
++//                Handled in GameData.BlockCallbacks - leaving tripwire as it seems to be special cased
+             }
+         }
+     }

src/main/java/net/minecraftforge/fml/common/registry/GameData.java

@@ -288,7 +288,10 @@ public class GameData
             ClearableObjectIntIdentityMap<IBlockState> blockstateMap = (ClearableObjectIntIdentityMap<IBlockState>)slaves.get(BLOCKSTATE_TO_ID);
             for (IBlockState state : block.getBlockState().getValidStates())
             {
-                blockstateMap.put(state, blockId << 4 | block.getMetaFromState(state));
+                final int meta = block.getMetaFromState(state); // meta value the block assigns for the state
+                final int bsmeta = blockId << 4 | meta; // computed blockstateid for that meta
+                final IBlockState blockState = block.getStateFromMeta(meta); // state that the block assigns for the meta value
+                blockstateMap.put(blockState, bsmeta); // store assigned state with computed blockstateid
             }
         }
 

src/test/java/net/minecraftforge/fml/common/registry/BlockStateMappingsTest.java

@@ -0,0 +1,61 @@
+package net.minecraftforge.fml.common.registry;
+
+import net.minecraft.block.Block;
+import net.minecraft.block.BlockDirt;
+import net.minecraft.block.material.Material;
+import net.minecraft.block.properties.PropertyBool;
+import net.minecraft.block.properties.PropertyInteger;
+import net.minecraft.block.state.BlockStateContainer;
+import net.minecraft.block.state.IBlockState;
+import net.minecraft.init.Blocks;
+import net.minecraft.init.Bootstrap;
+import net.minecraft.util.ResourceLocation;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.world.IBlockAccess;
+import net.minecraftforge.fml.common.DummyModContainer;
+import net.minecraftforge.fml.common.Loader;
+import net.minecraftforge.fml.common.ModMetadata;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import javax.annotation.Nonnull;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Test block state mappings bidirectionality
+ */
+public class BlockStateMappingsTest
+{
+    @BeforeClass
+    public static void setup()
+    {
+        System.setProperty("fml.queryResult", "confirm");
+        System.setProperty("fml.doNotBackup", "true");
+        Loader.instance();
+        Bootstrap.register();
+        Loader.instance().setupTestHarness(new DummyModContainer(new ModMetadata() {{
+            modId = "test";
+        }}));
+    }
+
+    @Test
+    public void testBlockStates()
+    {
+        // stems have a problem where the blockstate for meta 0 is not the same in the blockstate map and from block.getStateFromMeta
+        // This test asserts that the two values should be equivalent
+        // Specifically, in vanilla the state for meta 0 in the blockstatemap is facing=east,age=0 but the block says it's facing=up,age=0
+        Block bl = Blocks.MELON_STEM;
+        int id = Block.getIdFromBlock(bl);
+        for (int meta = 0; meta < 8; meta++)
+        {
+            int realbsm = id << 4 | meta; // computed blockstateid for this meta
+            IBlockState realst = bl.getStateFromMeta(meta); // The state that the block assigns to this meta
+            int bsm = GameData.getBlockStateIDMap().get(realst); // The blockstateid for the meta's state
+            IBlockState foundst = GameData.getBlockStateIDMap().getByValue(realbsm); // The state that is stored for the computed blockstateid
+            assertEquals("Got computed blockstate ids that match", realbsm, bsm);
+            assertEquals("Got equal states", realst, foundst);
+        }
+    }
+
+}