{"ast_node_type":"other","tokens":[{"end":99,"kind":"keyword","start":0,"text":"//"}]}
                                // but `lt.span` only points at `'_`, so to suggest `-> Option<()>`
                                // fn g(mut x: impl Iterator<Item = &'_ ()>) -> Option<&'_ ()>
                                // we need to find a more accurate span to end up with