Add collisionExtendsVertically hook to allow modded blocks that extend collision into the block above similar to fences. (#6092)

src/main/java/net/minecraftforge/common/extensions/IForgeBlock.java

@@ -29,6 +29,7 @@ import javax.annotation.Nullable;
 import net.minecraft.block.Block;
 import net.minecraft.block.BedBlock;
 import net.minecraft.block.FarmlandBlock;
+import net.minecraft.block.FenceGateBlock;
 import net.minecraft.block.FireBlock;
 import net.minecraft.block.HorizontalBlock;
 import net.minecraft.block.IBeaconBeamColorProvider;
@@ -1024,4 +1025,13 @@ public interface IForgeBlock
         world.setBlockState(pos, Blocks.AIR.getDefaultState(), 3);
         getBlock().onExplosionDestroy(world, pos, explosion);
     }
+
+    /**
+     * Determines if this block's collision box should be treated as though it can extend above its block space.
+     * Use this to replicate fence and wall behavior.
+     */
+    default boolean collisionExtendsVertically(BlockState state, IBlockReader world, BlockPos pos, Entity collidingEntity)
+    {
+        return getBlock().isIn(BlockTags.FENCES) || getBlock().isIn(BlockTags.WALLS) || getBlock() instanceof FenceGateBlock;
+    }
 }

src/main/java/net/minecraftforge/common/extensions/IForgeBlockState.java

@@ -867,4 +867,13 @@ public interface IForgeBlockState
     {
         getBlockState().getBlock().onBlockExploded(getBlockState(), world, pos, explosion);
     }
+
+    /**
+     * Determines if this block's collision box should be treated as though it can extend above its block space.
+     * This can be used to replicate fence and wall behavior.
+     */
+    default boolean collisionExtendsVertically(IBlockReader world, BlockPos pos, Entity collidingEntity)
+    {
+        return getBlockState().getBlock().collisionExtendsVertically(getBlockState(), world, pos, collidingEntity);
+    }
 }