syntax_data: {"ast_node_type":"variable","tokens":[{"end":29,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let source_info =
context_before:         for (argument_index, param) in arguments.iter().enumerate() {
context_after:                 SourceInfo::outermost(param.pat.as_ref().map_or(self.fn_span, |pat| pat.span));