用法

在项目上放置 #[cfg_attrs] 将启用一个 #[configure(<condition>, <attributes>)] 辅助属性，以便在该项目上使用。

该 #[configure(...)] 属性的语法类似于 #[cfg_attr(...)]，但配置属性使用完整的属性语法。这种方法的优点是，文档注释，扩展为 #[doc = "..."] 属性，可以在 #[configure(...)] 语法中使用。

示例

#[cfg_attrs]
/// This is an example struct.
#[configure(
    debug_assertions,
    ///
    /// Hello! These are docs that only appear when
    /// debug assertions are active.
)]
enum Example {
    #[configure(
        feature = "magic",
        /// Woah! Look at that! It enables
        /// `#[configure(...)]` for variants too!
    )]
    Point {
        #[configure(
            feature = "magic",
            /// And fields! This is amazing!
        )]
        x: i32,
        y: i32,
    },
}

这将展开为以下 #[cfg_attr(...)] 的用法

/// This is an example enum.
#[cfg_attr(
    debug_assertions,
    doc = "",
    doc = " Hello! These are docs that only appear when",
    doc = " debug assertions are active."
)]
enum Example {
    #[cfg_attr(
        feature = "magic",
        doc = " Woah! Look at that! It enables",
        doc = " `#[configure(...)]` for variants too!"
    )]
    Point {
        #[cfg_attr(
            feature = "magic",
            doc = " And fields! This is amazing!"
        )]
        x: i32,
        y: i32,
    },
}

如果调试断言处于活动状态，则会被展开为

/// This is an example enum.
///
/// Hello! These are docs that only appear when
/// debug assertions are active.
enum Example {
    Point {
        x: i32,
        y: i32,
    },
}

或者，如果启用了 magic 功能

/// This is an example enum.
enum Example {
    /// Woah! Look at that! It enables
    /// `#[configure(...)]` for variants too!
    Point {
        /// And fields! This is amazing!
        x: i32,
        y: i32,
    },
}

#[cfg_attrs(...)] 也可以与除文档注释之外的属性一起使用，尽管这样做没有实际的好处

#[cfg_attrs]
#[configure(
    feature = "magic",
    #[sparkles]
    #[crackles]
)]
fn bewitched() {}

以下示例展开为

#[cfg_attr(feature = "magic", sparkles, crackles)]
fn bewitched() {}

并且如果启用了 magic 功能，则会展开为

#[sparkles]
#[crackles]
fn bewitched() {}