syntax_data: {"ast_node_type":"variable","tokens":[{"end":80,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let with_whitespace = sm.span_extend_while_whitespace(arm_span);
context_before:                 // If the arm is followed by a comma, extend the span to include it.
context_after:                 if let Some(comma) = sm.span_look_ahead(with_whitespace, ",", Some(1)) {