syntax_data: {"ast_node_type":"variable","tokens":[{"end":70,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                     let discr = this.temp(discr_ty, source_expr.span);
context_before:                     let temp = unpack!(block = this.as_temp(block, scope, source, Mutability::Not));
context_after:                     this.cfg.push_assign(