pub fn gather_attrs(attrs: &[Attribute]) -> Vec<Result<(InternedString, Level, Span), Span>>
Parse the lint attributes into a vector, with Errs for malformed lint
attributes. Writing this as an iterator is an enormous mess.
Prefix searches with a type followed by a colon (e.g.
fn:) to restrict the search to a given type.
Accepted types are: fn, mod,
struct (or str), enum,
trait, typedef (or
tdef).