a6caceee4d
minor `effects` cleanups * remove the fixme comment about not needing defaults because it turns out we do need defaults (if I made it None instead it would ice a bunch of tests) * remove the part that special cased trait args when lowering them. This is now historical because effects doesn't add host args to traits anymore (we use associated types now)
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.