syntax_data: {"ast_node_type":"variable","tokens":[{"end":71,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:                 let a_ty = cx.type_of(au.def).instantiate(cx, au.args);
context_before:             if cfg!(debug_assertions) {
context_after:                 let b_ty = cx.type_of(bu.def).instantiate(cx, bu.args);