syntax_data: {"ast_node_type":"other","tokens":[{"end":37,"kind":"keyword","start":0,"text":"#[cfg(feature"}]}
source_snippet:             #[cfg(feature = "rustc")]
context_before:         let into_set = |alts: Vec<_>| {
context_after:             let mut set = rustc_data_structures::fx::FxIndexSet::default();