Remove tag if new tag value is empty.

[madelinekalil]

If the new tag value is the empty string,
set the Tag to be nil. Having empty but
non-nil tags causes formatting issues
that leave trailing whitespace.

[findleyr]

LGTM, with one nit. Thanks for tracking this down!

[findleyr]

I think it would be clearer to defer mutating f.Tag until this point. In other words, on line 104 above, just do something like

curTag := ""
if f.Tag != nil {
  curTag = f.Tag.Value
}

And then here, do:

if res == "" {
  f.Tag = nil
} else {
  if f.Tag == nil {
    f.Tag = &ast.BasicLit{}
  }
  f.Tag.Value = res
}

The advantage of this is that we don't run the risk of leaving an empty, non-nil tag in the tree if we encounter an error. Also, it generally is easier to follow the code if state mutation is left until the end.

[findleyr]

@fatih this is just a bug fix. If you're OK with it, can you approve?

[fatih]

@findleyr are you OK if I add you as a collaborator so you can approve and merge PR's?

[findleyr]

@fatih sure, I can do that. I probably won't be able to offer much support, but can help fix bugs related to our usage.