{"ast_node_type":"variable","tokens":[{"end":72,"kind":"keyword","start":0,"text":"let"}]}
    let arg_list = expr.syntax().parent().and_then(ast::ArgList::cast)?;
fn from_param(expr: &ast::Expr, sema: &Semantics<'_, RootDatabase>) -> Option<SmolStr> {
    let args_parent = arg_list.syntax().parent()?;