Change Wrap() to return an error even if we provide nil about errors

[davecheney]

Thank you for raising this issue. Would you mind confirming if it is a duplicate of an exisiting issue. Thank you.

[silbinarywolf]

Ah I'm so sorry. I looked through open issues but not closed ones. I now see there's been discussion elsewhere here and multiple other places:
#228
#90

Considering this problem keeps being raised, is it worth adding code comments so that it's clear that the behaviour won't change + intention is that you just fork it yourself?

[puellanivis]

I am not really sure what additional benefit would come from adding more code comments to the already well documented behavior. You clearly understood that this change could be a breaking change, and I think once people are aware of the behavior, they can also work out the implications of changing it.

I feel like there's just a use-case I'm missing here.

func f(data []byte, v interface{}) error {
  return errors.Wrap(json.Unmarshal(data, v), "context to the possible error")
}

func g(data []byte) error {
  _, err := w.Write(data)
  return errors.Wrap(err, "context to the possible error")
}

Additionally, there is a semantics argument: any wrapping of a non-error should be a non-error, right? That is, it doesn’t really make sense to turn a non-error into an error. A wrapped error with no cause is… weird.

In particular, your given code example, even without errors.Wrap was still buggy:

func someFunction(ctx context.Context) (*Page, error) {
    // ... pretend there's more code here that created `nstmt` variable or anything else i've missed.
    var pageList []Page
    err := nstmt.SelectContext(ctx, &pageList, map[string]interface{}{
        "id": request.ID,
    })
    if err != nil {
        return nil, err
    }
    if len(pageList) == 0 {
        // This is still a mistake, and one that I have seen in the wild from time to time.
        return nil, err
    }
}