syntax_data: {"ast_node_type":"variable","tokens":[{"end":39,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let mut marks = Vec::new();
context_before:             let mut glob_ctxt = data.normalize_to_macros_2_0(glob_span.ctxt());
context_after:             while !data.is_descendant_of(expn_id, data.outer_expn(glob_ctxt)) {