c905e9d0ca
Improve trait/impl method discrepancy errors * Use more accurate spans * Clean up some code by removing previous hack * Provide structured suggestions Structured suggestions are particularly useful for cases where arbitrary self types are used, like in custom `Future`s, because the way to write `self: Pin<&mut Self>` is not necessarily self-evident when first encountered.
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.