syntax_data: {"ast_node_type":"struct","tokens":[{"end":80,"kind":"keyword","start":0,"text":"///"}]}
source_snippet: /// Construct a diagnostic for a language feature error due to the given `span`.
context_before: // todo: this function now accepts `Session` instead of `ParseSess` and should be relocated
context_after: /// The `feature`'s `Symbol` is the one you used in `unstable.rs` and `rustc_span::symbol`.