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

Question

我正在尝试最新测试版 clap 的索引页面上的“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。

我很欣赏这是一个测试版，但是这个功能是否可以正常工作，还是我做错了什么？

谢谢！

Answer 1

在 clap 中，在Cargo.toml使用features = [ "derive" ]来启用派生的能力:)