使用自定义结构和使用宏编译 Rust 项目失败

Question

我开始学习 Rust 并尝试项目的结构。 现在我有这样的项目结构：

project
└─── src
│   └─── core
│   │   └─── lib.rs
│   │   └─── Cargo.toml
│   └─── api
│       └─── main.rs
│       └─── Cargo.toml
└─── Cargo.toml

toml文件内容如下：

project/Cargo.toml

[workspace]
members = [ 
    "src/core", 
    "src/api"
]

project/src/api/Cargo.toml

[package]
name = "api"
version = "0.1.0"

[[bin]]
name = "api"
path = "main.rs"

[dependencies]
core = { path = "../core" }
rocket =  { version = "0.5.0", features = ["json"] } 

使用这些设置，如果在

main.rs

中我正在尝试使用火箭宏，则不会编译该项目。

main.rs

（代码取自火箭包的描述）：

#[macro_use] extern crate rocket;

#[get("/<name>/<age>")]
fn hello(name: &str, age: u8) -> String {
    format!("Hello, {} year old named {}!", age, name)
}

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/hello", routes![hello])
}

我收到错误：

macro-expanded `macro_export` macros from the current crate cannot be referred to by absolute paths
this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
for more information, see issue #52234 <https://github.com/rust-lang/rust/issues/52234>

这是什么原因以及如何解决？

但是

我尝试用src文件夹创建一个api项目，这个问题不再重复。

api
└─── src
│   └─── main.rs
└─── Cargo.toml

但我不想保留每个项目（main 和 lib）的 src 文件夹，因为工作区已经有 src。对此可以做什么？

执行

cargo check

命令的结果：

error: macro-expanded `macro_export` macros from the current crate cannot be referred to by absolute paths
 --> src\api\main.rs:4:4
  |
4 | fn hello(name: &str, age: u8) -> String {
  |    ^^^^^
  |
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: for more information, see issue #52234 <https://github.com/rust-lang/rust/issues/52234>     
note: the macro is defined here
 --> src\api\main.rs:3:1
  |
3 | #[get("/<name>/<age>")]
  | ^^^^^^^^^^^^^^^^^^^^^^^
  = note: `#[deny(macro_expanded_macro_exports_accessed_by_absolute_paths)]` on by default
  = note: this error originates in the attribute macro `get` (in Nightly builds, run with -Z macro-backtrace for more info)

error: could not compile `api` (bin "api") due to 1 previous error

Answer 1

看起来 Rocket 文档有一段时间没有更新了，因为

#[macro_use]

语法在 Rust 1.30 中被淘汰了。只需通过 use 声明导入这些宏，如下所示：

use rocket::{get, launch, routes};

#[get("/<name>/<age>")]
fn hello(name: &str, age: u8) -> String {
    format!("Hello, {} year old named {}!", age, name)
}

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/hello", routes![hello])
}

此代码可以编译。