chore: use fmt.Errorf and fix add checks

[stevenh]

Update to use stdlib fmt.Errorf with %w for wrapping.

Use idiomatic errors:

• Lower case
• Describe the action not the failure
• Remove "Error" as that's given since its an error
• Always report the original cause
• Quote file names using %q to its easy to identify trailing spaces

Add missing error checks.

[ybirader]

Thanks for the PR!

The majority of the changes are fine. However, I intentionally chose errors over using fmt- the reason is that fmt does not allow any context/debugging info, which means it can be hard to see the failure path.

Until Go 2, I think we should stick with errors.

Apart from that, everything looks fine.

[stevenh]

To confirm my understanding by context do you mean source of the error?

If so that's why each error now uses %w which ensures the context is captured, playground example to demonstrate

Code is fine.

[ybirader]

Thanks- completely missed the %w!