Antipattern in some (custom) error type assertions

[fako1024]

The implementation from #250 contains a few type assertions which are not safe, e.g.

if err != nil {
    // if there's an args error, print it in a user-friendly way
    prettyErr, ok := err.(types.Prettier)
...

or

switch t := err.(type) {
case *query.ArgsError:
    vr.ArgsError = t
default:
    LogAndAbort(ctx, c, http.StatusInternalServerError, err)
    return
}

The issue with these assertions is that they won't work on wrapped errors (which may or may not be present, but might of course at any point in time). Best practices suggest to use errors.As() instead.

[fako1024]

@els0r FYI.

[els0r]

Thanks for reporting and the suggestion.

Let's make sure to clean this before 4.1.