Multi-line string literals are in, but we need better diagnostics such as notes telling why the literal is invalid, and in some cases fixits.
Potential way to attack this:
1) For each comment (that doesn't start with "expected-error" in https://github.com/apple/swift/blob/master/test/Parse/multiline_errors.swift, make a note to help inform the user why the literal is invalid.
2) When it makes sense, also add a fixit (e.g. if it's obvious that a line needs extra indentation).