{"ast_node_type":"function","tokens":[{"end":71,"kind":"keyword","start":0,"text":"fn"}]}
                fn fn_ctr_self() fn() -> Option<Foo> [type_could_unify]
                fn fn_ctr() fn() -> Foo [type_could_unify]
                fn fn_another(…) fn(u32) -> Other [type_could_unify]