syntax_data: {"ast_node_type":"variable","tokens":[{"end":58,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let source = self.parse_operand(*source)?;
context_before:             ExprKind::Cast { source } => {
context_after:                 let source_ty = source.ty(self.body.local_decls(), self.tcx);