Function render_face_list 

pub fn render_face_list(field: &str, value: &str) -> String

Render one comma-separated value as a quoted list field, indented and newline-terminated; an empty value renders as nothing at all. 把一个逗号分隔的取值渲染成带引号的列表字段（缩进且以换行结尾）；取值为空时不渲染任何 内容。

The empty case is the point: a field with no entries must disappear from the macro rather than appear as field: [], because the authoring writer diffs the rendered text and an empty-but-present field would look like an edit. 空取值这一点是关键：没有条目的字段必须从宏里消失，而不是写成 field: []——创作写入方 会对渲染文本做差异比较，“存在但为空“的字段会被当成一次修改。