syntax_data: {"ast_node_type":"other","tokens":[{"end":22,"kind":"keyword","start":0,"text":"user_ty:"}]}
source_snippet:         user_ty: None,
context_before:         span: source_info.span,
context_after:         const_: Const::Val(ConstValue::from_target_usize(0, &tcx), tcx.types.usize),