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.
• Dependencies (accounts for target-specific ones, but not optional ones currently):
  • #[realia::dep("your-crate", "foo")]
    • Checks if your crate uses any version of the foo crate.
  • #[realia::dep("your-crate", "foo", "1.2.3")]
    • Checks if your crate uses the foo crate with exactly version 1.2.3.
  • #[realia::dep_since("your-crate", "foo", "1.2.3")]
    • Checks if your crate uses the foo crate with version 1.2.3 or newer.
  • #[realia::dep_before("your-crate", "foo", "1.2.3")]
    • Checks if your crate uses the foo crate with a version before 1.2.3.
  • #[realia::dep_from_registry("your-crate", "foo")]
    • Checks if your crate uses the foo crate from the registry (as opposed to being a git or path dependency). This is useful if you have publishing fallbacks.

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

If you use the env or cmd attributes,you'll need to include a build.rs in your project with any 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");
}