The best thing about this is the open issue claiming it's "Too much like the real Terraria source code." [1] :) This bring back a lot of memories. Way, way back in the day i wrote a clone of Battle City [2] in XNA with a half-decent AI. I had intentions to learn and use some OOP patterns. I ended up with a handful of monstrous classes and generally a clusterfuck of spaghetti code. But... i learned a lot about AI and…
Holy shit. Be sure to read the issue. It turns out it's not really a joke - someone in the know points out that Terraria's code is basically the same quality, if not worse...
These days there are a fair amount of production Unity games out that you can extract full sources for.. Can make for a fun read sometimes.