{"ast_node_type":"other","tokens":[{"end":129,"kind":"keyword","start":0,"text":"//"}]}
                // See https://github.com/rust-lang/rust/blob/b0af276da341/compiler/rustc_expand/src/mbe/transcribe.rs#L724-L726.
                // `${concat}` span comes from the macro (at least for now).
                let mut result_span = *concat_span;