带有派生宏的 Clap 选项无法在 rust clap 3.0.0-beta.5 中编译

Question

我正在尝试最新 beta 版 clap索引页上的“使用派生宏”示例：

// (Full example with detailed comments in examples/01d_quick_example.rs)
//
// This example demonstrates clap's full 'custom derive' style of creating arguments which is the
// simplest method of use, but sacrifices some flexibility.
use clap::{AppSettings, Parser};

/// This doc string acts as a help message when the user runs '--help'
/// as do all doc strings on fields
#[derive(Parser)]
#[clap(version = "1.0", author = "Kevin K. <kbknapp@gmail.com>")]
struct Opts {
    /// Sets a custom config file. Could have been an Option<T> with no default too
    #[clap(short, long, default_value = "default.conf")]
    config: String,
    /// Some input. Because this isn't an Option<T> it's required to be used
    input: String,
    /// A level of verbosity, and can be used multiple times
    #[clap(short, long, parse(from_occurrences))]
    verbose: i32,
    #[clap(subcommand)]
    subcmd: SubCommand,
}
...

不幸的是它无法编译：

$ cargo build
   Compiling ex v1.0.0-SNAPSHOT (/home/hwalters/git/home/ex)
error: cannot find derive macro `Parser` in this scope
 --> src/main.rs:5:10
  |
5 | #[derive(Parser)]
  |          ^^^^^^
  |
note: `Parser` is imported here, but it is only a trait, without a derive macro
 --> src/main.rs:1:25
  |
1 | use clap::{AppSettings, Parser};
  |                         ^^^^^^

error: cannot find attribute `clap` in this scope
 --> src/main.rs:6:3
  |
6 | #[clap(version = "1.0", author = "Kevin K. <kbknapp@gmail.com>")]
  |   ^^^^
  |
  = note: `clap` is in scope, but it is a crate, not an attribute
...

我试图在这个 GitHub 标签的tar 文件中找到完整的示例文件“examples/01d_quick_example.rs” ，但它似乎不存在。

我很高兴这是测试版，但此功能是否可以正常工作，或者我做错了什么？

谢谢！

Answer 1

在拍手中，features = [ "derive" ]使用Cargo.toml来启用派生能力:)

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更新

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下面的@stein很好地扩展了答案：

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“使用”的意思是：在 [依赖项] 部分中，使用类似于以下内容的行指定 clap： clap = { version = "3.1.0", features = ["derive"]} \xe2\x80\x93\xc2\ xa0\n斯坦因 2 月 19 日 13:00

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请+1 他们的评论:-)。

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这意味着，在你的Cargo.toml

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[dependencies]\n# ...\nclap = { version = "3", features = ["derive"]}\n

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