syntax_data: {"ast_node_type":"variable","tokens":[{"end":72,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                     let b = self.infcx.instantiate_binder_with_infer(b);
context_before:                 self.infcx.enter_forall(a, |a| {
context_after:                     self.relate(a, b)