Hopper
Adds hoppers to Minecraft! Hoppers are an easy-to-use, simple system for transporting items between chests. The Hopper is crafted with a chest and 5 iron. If it's not powered by redstone, it takes items out of the container on its top face (or collects items lying on the ground in that location), and deposits them into the container it's pointing at. The hopper can also be placed upside down, for adding items into the fuel slot of a furnace, say.
It also adds a Block of Redstone. In the world, it's a piston-pushable, solid-block redstone power source. As an item, it acts as a convenient storage block for all that redstone dust you have lying around.
Mod compat
The hopper should work with all standard inventories, and anything that works with standard inventories should work with it. This counts as mod compat, right?
Code style
Not a coremod. I've never heard of Mixins in my life.
License
Code and buildscript is nominally LGPL-3.0-or-later, but with my usual "I literally do not give a damn if you take stuff for learning purposes and ship it in a released mod" exception. We're all figuring this shit out together, ok?
And a special thanks to unascribed and TwilightFlower.