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如何正确地将包含双冒号的路径传递给此宏?

rust-macros rust

0

Jamie · 技术社区 · 8 月前

我在用 schemars 在我的代码库中广泛存在,我正在用以下(简化)类型填充一个相当大的向量:

#[derive(Serialize, Deserialize, Debug, Clone)]
pub struct CommandDescription {
    /// The name for the command/action as it would appear in the JSON.
    pub cmd: String,
    /// Parameters the command takes
    pub parameters: Option<RootSchema>,
}

结构的完整定义有更多的字段,它们是以下字段的组合 String 和 RootSchema 类型。

在我的代码中,我有数百种这样的定义:

CommandDescription {
    cmd: String::from(api_schema::about::ABOUT_CMD),
    parameters: Some(schema_for!(api_schema::about::AboutCmd)),
},

我想创建一个宏,但我很难 schema_for!() 宏。

我的宏观定义是:

macro_rules! command_description {
    ($api_path:path, $prefix:ident, $type_name_cmd:ident) => {
        CommandDescription {
            cmd: String::from(concat!(
                stringify!($api_path),
                "::",
                stringify!($prefix),
                "_CMD"
            )),
            parameters: Some(schema_for!($api_path::$type_name_cmd)),
        }
    };
}

我援引:

    command_description!(
        api_schema::about,
        ABOUT,
        AboutCmd
    )

但编译器建议我封装 $api_path 在 schema_for!() 宏放在尖括号中,但它是一个路径,而不是一个类型:我知道这一点,因为如果我添加 <$api_path> 我听说这不是一种类型。

error: missing angle brackets in associated item path
   --> src/bin/rudi-service.rs:674:42
    |
674 |               parameters: Some(schema_for!($api_path::$type_name_cmd)),
    |                                            ^^^^^^^^^
    = note: this error originates in the macro `command_description` (in Nightly builds, run with -Z macro-backtrace for more info)
help: types that don't start with an identifier need to be surrounded with angle brackets in qualified paths
    |
674 |             parameters: Some(schema_for!(<$api_path>::$type_name_cmd)),
    |                                          +         +

我是否使用了错误的片段说明符 $api_path 参数?

1 回复 | 直到 8 月前

1

2

Chayim Friedman 8 月前

问题是,一旦某样东西被捕获为 path (或大多数其他片段说明符),它不能再被分解,也不能用更多的片段进行扩展。解决方案是单独捕获分段:

macro_rules! command_description {
    ($($api_path:ident)::+, $prefix:ident, $type_name_cmd:ident) => {
        CommandDescription {
            cmd: String::from(concat!(
                stringify!($($api_path)::+),
                "::",
                stringify!($prefix),
                "_CMD"
            )),
            parameters: Some(schema_for!($($api_path)::+::$type_name_cmd)),
        }
    };
}