Macro rerun_if_env_changed

macro_rules! rerun_if_env_changed {
    ($($tokens:tt)*) => { ... };
}

The rerun_if_env_changed instruction tells Cargo to re-run the build script if the value of an environment variable of the given name has changed.

Note that the environment variables here are intended for global environment variables like CC and such, it is not possible to use this for environment variables like TARGET that Cargo sets for build scripts. The environment variables in use are those received by cargo invocations, not those received by the executable of the build script.

For more information, see this cargo reference.