syntax_data: {"ast_node_type":"other","tokens":[{"end":19,"kind":"keyword","start":0,"text":"#[track_caller]"}]}
source_snippet:     #[track_caller]
context_before:     /// `feature` must be a language feature.
context_after:     pub fn create_feature_err<'a>(&'a self, err: impl Diagnostic<'a>, feature: Symbol) -> Diag<'a> {