syntax_data: {"ast_node_type":"variable","tokens":[{"end":64,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let outlives = ty::OutlivesPredicate(source, r);
context_before:                 // being cast to `Foo + 'a` outlives `'a`:
context_after:                 nested.push(predicate_to_obligation(