如果禁用相关功能，如何跳过依赖项

Question

假设我有一个箱子，只有在glob启用时才依赖#[cfg(feature = "glob")]箱子。此外，默认情况下禁用此功能。如何在默认情况下跳过下载和编译glob包？

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

[dependencies]
glob = "0.2"
...

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

必须将glob依赖项标记为可选：

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