{"ast_node_type":"variable","tokens":[{"end":57,"kind":"keyword","start":0,"text":"let"}]}
    let (fn_type, tail_expr, return_type_range, action) =
fn extract_tail(ctx: &AssistContext<'_>) -> Option<(FnType, ast::Expr, InsertOrReplace)> {
        if let Some(closure) = ctx.find_node_at_offset::<ast::ClosureExpr>() {