syntax_data: {"ast_node_type":"variable","tokens":[{"end":76,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:             let layout: Tree<Def, !, !> = Tree::def(Def::NoSafetyInvariants)
context_before:         fn invisible_def_in_seq_len_3() {
context_after:                 .then(Tree::byte(0x00))