[shepmaster]

I partially agree. I have been experimenting with creating a lot of small error types (e.g. one per function) because of the benefit of narrowing down the set of possible causes. I also dislike crate-wide errors for the same reason.

However, having an anonymous sum type isn’t a good solution here because there’s nowhere for you to add context to. It’s not useful for your final error to say “permission denied” without the context of a file name, or knowing that you were trying to open configuration file, etc.

Also, depending on your implementation, you either cannot allow multiple errors of the same underlying cause (e.g. two IO errors, one for writing and one for opening) because they are the same type or you have positional error tuples (error index 0 is write, index 1 is open). Neither of those is super ergonomic.