rust - 如何使用 rustc-env 标志指定环境变量？

Question

我想设置 rustc-env=VAR=VALUE 以便我可以在我的代码中使用 env::var("VAR") 访问它。但是，我不清楚在哪里指定它。我可以在 Makefile 中设置环境变量 VAR 吗？

Answer 1

长话短说

build.rs

fn main() {
    println!("cargo:rustc-env=VAR=VALUE");
}

src/main.rs

fn main() {
    let var = env!("VAR");
}

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documentation that you linked用于 Cargo 构建脚本:

The Rust file designated by the build command (relative to the package root) will be compiled and invoked before anything else is compiled in the package, allowing your Rust code to depend on the built or generated artifacts. By default Cargo looks up for "build.rs" file in a package root (even if you do not specify a value for build). Use build = "custom_build_name.rs" to specify a custom build name or build = false to disable automatic detection of the build script.

在同一页上，有一个 section that describes outputs of build.rs

All the lines printed to stdout by a build script are written to a file [...] Any line that starts with cargo: is interpreted directly by Cargo. This line must be of the form cargo:key=value, like the examples below:

cargo:rustc-env=FOO=bar

然后详细说明rustc-env:

rustc-env=VAR=VALUE indicates that the specified environment variable will be added to the environment which the compiler is run within. The value can be then retrieved by the env! macro in the compiled crate. This is useful for embedding additional metadata in crate's code, such as the hash of Git HEAD or the unique identifier of a continuous integration server.

env!是一个宏。

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access it using env::var("VAR")

没有。 env::var用于读取程序运行时设置的环境变量，而不是程序编译时设置的。

另见:

• Is it possible to initialize a variable from an environment variable at compilation time when using no_std?