Realia

This crate provides macros for conditional compilation based on various checks. These macros are analogous to #[cfg(...)] and #[cfg_attr(...)].

Realia is inspired by and heavily based on rustversion.

Attributes

Primary:

• Environment variables:
  • #[realia::env("FOO")]
    • Checks if the FOO environment variable exists.
  • #[realia::env("FOO", "bar")]
    • Checks if the FOO environment variable has the value bar.
• Executables:
  • #[realia::cmd("foo")]
    • Checks if the executable foo exists in the PATH environment variable.

The above can be refined or augmented by these additional attributes:

• #[realia::not(env("FOO"))]
  • Inverts the condition.
• #[realia::any(env("FOO"), env("bar"))]
  • Checks if any of the conditions are met.
• #[realia::all(env("FOO"), env("bar"))]
  • Checks if all of the conditions are met.
• #[realia::attr(env("FOO"), some_attr)]
  • Applies #[some_attr] if the condition is met. You can also specify const this way.

Triggering build on changed conditions

To trigger builds when the conditions change, you'll need to include a build.rs in your project with the environment variables you check.

fn main() {
    // Necessary when using #[realia::env("FOO")]
    println!("cargo:rerun-if-env-changed=FOO");

    // Necessary when using #[realia::cmd(...)]
    println!("cargo:rerun-if-env-changed=PATH");
}