syntax_data: {"ast_node_type":"variable","tokens":[{"end":63,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let outlives = ty::OutlivesPredicate(r_a, r_b);
context_before:                 // Register one obligation for 'a: 'b.
context_after:                 obligations.push(Obligation::with_depth(