{"ast_node_type":"function","tokens":[{"end":69,"kind":"keyword","start":0,"text":"fn"}]}
                fn fn_builder() fn() -> FooBuilder [type_could_unify]
                fn fn_ctr_with_args(…) fn(T) -> Foo<T> [type_could_unify]
                fn fn_ctr() fn() -> Option<Foo<T>> [type_could_unify]