The concepts aren't wrong (structured logs from structured errors), but I find this code to be very un-go-like and there are obvious signs of trying to write java in go (iFace, structs with one property "because everything needs to be contained in an object", and others).
Return "error" and not a custom type "mypkg.Error" - you run into more nil interface pointer problems and you are breaking an idiom.
Let me provide a counter example for helping create structured logs from structured errors that I wrote up that is much more idiomatic if not more narrowly focused:
As in the article, if you want to attach "username: foo", this package lets you return kverr.New(err, "username", foo, ...), and then extract a slice or map later for logging like logger.WithArgs(YoinkArgs(err)...).
Return "error" and not a custom type "mypkg.Error" - you run into more nil interface pointer problems and you are breaking an idiom.
Let me provide a counter example for helping create structured logs from structured errors that I wrote up that is much more idiomatic if not more narrowly focused:
https://github.com/sethgrid/kverr
As in the article, if you want to attach "username: foo", this package lets you return kverr.New(err, "username", foo, ...), and then extract a slice or map later for logging like logger.WithArgs(YoinkArgs(err)...).