Macros 无法导入/导出宏

我有一个名为

macros.rs

的模块，其中包含

/// Macro to easily implement FromError.
/// from_error!(MyError, IoError, MyError::IoError)
macro_rules! from_error {
    ( $t:ty, $err:ty, $name:path ) => {
        use std;
        impl std::error::FromError<$err> for $t {
            fn from_error(err: $err) -> $t {
                $name(err)
            }
        }
    }
}

---

当我尝试在项目的其他模块中使用

from\u error

时，编译器会说

error:macro undefined:“from\u error！”
结果表明，声明模块的顺序很重要

mod json; // json uses macros from the "macros" module. can't find them.
#[macro_use]
mod macros;

#[macro_use]
mod macros;
mod json; // json uses macros from the "macros" module. everything's ok this way.

mod json; // json uses macros from the "macros" module. can't find them.
#[macro_use]
mod macros;

#[macro_use]
mod macros;
mod json; // json uses macros from the "macros" module. everything's ok this way.