Rust wasm-pack编译警告E0446：公共接口含私有类型World

问题代码 #

use wasm_bindgen::prelude::*;

#[global_allocator]
static ALLOC: wee_alloc::WeeAlloc = wee_alloc::WeeAlloc::INIT;

#[wasm_bindgen]
struct World {
    width: usize
}

#[wasm_bindgen]
impl World {
    pub fn new() -> World {
        World {
            width :8
        }
    }

    pub fn width(&self) -> usize {
            self.width
    }
}

编译警告信息 #

[INFO]: 🌀  Compiling to Wasm...
   Compiling snake_game v0.1.0 (C:\dev\my\rust\test\snake_game)
warning: private type `World` in public interface (error E0446)
  --> src\lib.rs:11:1
   |
11 | #[wasm_bindgen]
   | ^^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: `#[warn(private_in_public)]` on by default
   = note: this warning originates in the attribute macro `wasm_bindgen::prelude::__wasm_bindgen_class_marker` (in Nightly builds, run with -Z macro-backtrace for more info)

问题原因（大白话） #

Rust里默认结构体是私有类型，只能在当前模块内部使用，但你通过#[wasm_bindgen]把World的构造方法new和width方法暴露给了外部（JS环境），这些公开方法的返回值用到了World类型——相当于把私有类型放到了公开接口里，逻辑上存在矛盾。Rust目前只是给出警告，未来会直接判定为错误。

解决办法 #

给World结构体加上pub关键字，让它变成公开类型，和你暴露的公开方法权限匹配：

#[wasm_bindgen]
pub struct World {
    width: usize
}

内容的提问来源于stack exchange，提问作者user63898