syntax_data: {"ast_node_type":"variable","tokens":[{"end":53,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let source_expr = &this.thir[source];
context_before:             ExprKind::ValueTypeAscription { source, ref user_ty, user_ty_span } => {
context_after:                 let temp = unpack!(