[1.17.x] implements canConnectRedstone(), Redstone dust now defers to the blockstate for determining connectivity (#8014)

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

@@ -719,4 +719,54 @@ public interface IForgeBlock
     {
         return state.is(Blocks.SCAFFOLDING);
     }
+
+    /**
+     * Whether redstone dust should visually connect to this block on a given side
+     * <p>
+     * The default implementation is identical to
+     * {@link RedStoneWireBlock#shouldConnectTo(BlockState, Direction)}
+     *
+     * <p>
+     * {@link RedStoneWireBlock} updates its visual connection when
+     * {@link BlockState#updateShape(Direction, BlockState, LevelAccessor, BlockPos, BlockPos)}
+     * is called, this callback is used during the evaluation of its new shape.
+     *
+     * @param state The current state
+     * @param world The world
+     * @param pos The block position in world
+     * @param direction The coming direction of the redstone dust connection (with respect to the block at pos)
+     * @return True if redstone dust should visually connect on the side passed
+     * <p>
+     * If the return value is evaluated based on world and pos (e.g. from BlockEntity), then the implementation of
+     * this block should notify its neighbors to update their shapes when necessary. Consider using
+     * {@link BlockState#updateNeighbourShapes(LevelAccessor, BlockPos, int, int)} or
+     * {@link BlockState#updateShape(Direction, BlockState, LevelAccessor, BlockPos, BlockPos)}.
+     * <p>
+     * Example:
+     * <p>
+     * 1. {@code yourBlockState.updateNeighbourShapes(world, yourBlockPos, UPDATE_ALL);}
+     * <p>
+     * 2. {@code neighborState.updateShape(fromDirection, stateOfYourBlock, world, neighborBlockPos, yourBlockPos)},
+     * where {@code fromDirection} is defined from the neighbor block's point of view.
+     */
+    default boolean canConnectRedstone(BlockState state, BlockGetter world, BlockPos pos, @Nullable Direction direction)
+    {
+        if (state.is(Blocks.REDSTONE_WIRE))
+        {
+            return true;
+        }
+        else if (state.is(Blocks.REPEATER))
+        {
+            Direction facing = state.getValue(RepeaterBlock.FACING);
+            return facing == direction || facing.getOpposite() == direction;
+        }
+        else if (state.is(Blocks.OBSERVER))
+        {
+            return direction == state.getValue(ObserverBlock.FACING);
+        }
+        else
+        {
+            return state.isSignalSource() && direction != null;
+        }
+    }
 }

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

@@ -641,4 +641,19 @@ public interface IForgeBlockState
     {
         return self().getBlock().isScaffolding(self(), entity.level, entity.blockPosition(), entity);
     }
+
+    /**
+     * Whether redstone dust should visually connect to this block on a side.
+     * <p>
+     * Modded redstone wire blocks should call this function to determine visual connections.
+     *
+     * @param world The world
+     * @param pos The block position in world
+     * @param direction The coming direction of the redstone dust connection (with respect to the block at pos)
+     * @return True if redstone dust should visually connect on the side passed
+     */
+    default boolean canRedstoneConnectTo(BlockGetter world, BlockPos pos, @Nullable Direction direction)
+    {
+        return self().getBlock().canConnectRedstone(self(), world, pos, direction);
+    }
 }