{"ast_node_type":"variable","tokens":[{"end":68,"kind":"keyword","start":0,"text":"let"}]}
    let (fn_type, tail_expr, builder_edit_pos) = extract_tail(ctx)?;
pub(crate) fn add_return_type(acc: &mut Assists, ctx: &AssistContext<'_>) -> Option<()> {
    let module = ctx.sema.scope(tail_expr.syntax())?.module();