syntax_data: {"ast_node_type":"variable","tokens":[{"end":57,"kind":"keyword","start":0,"text":"if"}]}
source_snippet:     if let Some('_' | '0'..='9') = ident.chars().next() {
context_before:     // Write a separating `_` if necessary (leading digit or `_`).
context_after:         output.push('_');