syntax_data: {"ast_node_type":"other","tokens":[{"end":56,"kind":"keyword","start":0,"text":"if"}]}
source_snippet:     if sess.psess.unstable_features.is_nightly_build() {
context_before:     // #23973: do not suggest `#![feature(...)]` if we are in beta/stable
context_after:         err.subdiagnostic(FeatureDiagnosticHelp { feature });