dependencies - 如何使本地依赖依赖于 Cargo 中的功能？

Question

鉴于这个在子目录中使用本地 crate 的小型库，我如何根据是否启用某个功能使其中一个依赖项成为可选的？

[package]
name = "image_load"
description = "Small wrapper for image reading API's."
version = "0.1.0"

[features]

default = ["use_png"]

[dependencies]

[dependencies.image_load_ppm]
path = "ppm"

# How to make this build _only_ when 'use_png' feature is enabled?
[dependencies.image_load_png]
path = "png"

当我阅读 the documentation ，这显示了如何拥有可选的外部 依赖项。在上面的示例中，我使用了一个本地子目录，我想根据某个功能构建或不构建它。

如何使 image_load_png 仅在启用 use_png 功能时构建。

Answer 1

这可以通过添加以下内容来完成:

[package]
name = "image_load"
version = "0.1.0"
description = "Small wrapper for image reading API's."

[features]

default = ["use_png"]
use_png = ["image_load_png"]  # <-- new line

[dependencies]

[dependencies.image_load_ppm]
path = "ppm"

[dependencies.image_load_png]
path = "png"
optional = true  # <-- new line

使用箱子是可选的。

例如:

#[cfg(feature = "use_png")]  // <-- new line
extern crate image_load_png;