Macro face_fields_mirror 

face_fields_mirror!() { /* proc-macro */ }

The editor-only field mirror used by generated aliases. 生成的别名使用的、仅供编辑器的字段镜像。 The editor-only field mirror for a declaration the caller already split. 为调用方已切分好的声明生成仅供编辑器的字段镜像。

The generated alias reaches this through face_fields_mirror!, because its token tree is opaque to an editor and the alias may be written with ; or in any order. Unlike the full front end it tolerates a field the author has not finished (kind: with no value) and never re-dispatches to the runtime. 生成的别名通过 face_fields_mirror! 走到这里：它的 token 树对编辑器不透明，而且别名 可能用 ; 或任意顺序书写。与完整前端不同，它容忍作者还没写完的字段（kind: 后面 还没有值），也绝不回派到运行期。