rust - 有没有办法只在测试期间从外部 crate 导入宏，而没有任何警告？

Question

我有这样的东西:

#[macro_use] extern crate log;

pub fn do_nothing() { let _ = log::Level::Info; }

#[cfg(test)]
mod tests {
    #[test]
    fn test_a() { debug!("Message."); }
}

编译时出现警告:

warning: unused `#[macro_use]` import

如果我删除宏导入，并将第一行更改为:

extern crate log;

然后我在编译时得到以下错误:

error: cannot find macro `debug!` in this scope

如果我然后尝试只为测试模块导入宏，即:

extern crate log;

pub fn do_nothing() { let _ = log::Level::Info; }

#[cfg(test)]

mod tests {
    #[macro_use] extern crate log;
    #[test]
    fn test_a() { debug!("Message."); }
}

然后我得到编译器错误:

error[E0468]: an `extern crate` loading macros must be at the crate root

是否有一种解决方案可以避免所有警告而不仅仅是抑制它们？

Answer 1

您可以使用cfg_attr:

#[cfg_attr(test, macro_use)]
extern crate log;

另见:

• Is it possible to conditionally derive with features?
• Can I conditionally compile my Rust program for a Windows subsystem?
• Run additional tests by using a feature flag to "cargo test"