Dependencies 如果相关功能被禁用，如何跳过依赖项

假设我有一个板条箱，它仅在启用了

#[cfg（feature=“glob”）]

时才依赖于

glob

板条箱。此外，此功能在默认情况下被禁用。默认情况下，如何跳过

glob

板条箱的下载和编译

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

[dependencies]
glob = "0.2"
...

和源代码：

# 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 
}

---

glob

依赖项必须标记为可选：

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