syntax_data: {"ast_node_type":"function","tokens":[{"end":20,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:         fn seq_1() {
context_before:         #[test]
context_after:             let layout: Tree<Def, !, !> = Tree::def(Def::NoSafetyInvariants).then(Tree::byte(0x00));