Package bug2638 reproduces go-swagger issue #2638 ("Improper handling of
multiple variables on one line"): a struct field group declaring several
names on one line (`R, G, B, A uint8`) must emit one property per name,
instead of a single mislabeled property.
type Mixed struct {
X, Y, Z float64 `json:"renamed,omitempty"`
Label string}
Mixed exercises a multi-name group alongside single-name fields, and a
multi-name group that carries json options: the `,omitempty` applies to
every member while the rename is dropped (a single rename can't name N
members).