dependencies - 如果相关功能被禁用，如何跳过依赖项

Question

假设我有一个 crate ，仅当启用 #[cfg(feature = "glob")] 时，该 crate 才依赖于 glob crate 。此外，该功能默认处于禁用状态。如何默认跳过 glob 包的下载和编译？

# Cargo.toml
...
[features]
default = []

[dependencies]
glob = "0.2"
...

以及源代码:

# lib.rs
.. several uses

#[cfg(feature = "glob")]
extern crate glob;

... a lot of code that doesn't use glob crate.

#[cfg(feature = "glob")]
impl Foo for Bar { 
    // only this code uses glob crate 
}

Answer 1

glob 依赖项必须标记为可选:

[dependencies]
glob = { version = "0.2", optional = true }