Also, I don't know if this was part of your critique, but are you also mentioning that the "a" variable is not in the suggestion? The reason behind that is long names, such as "super_special_file" would greatly increase the length of the error messages, making it hard to see the "meat" of what is being changed. Hence the x and y naming.

Perhaps I should add a flag to allow verbatim (or close to it) errors. Recreating the source lines exactly will be pretty hard, but I think we can do better here.