How do I create a Rust function or macro for debugging that gets optimized away in a release build?

Question

In a debug build, I want to check for OpenGL errors after almost every OpenGL call to ease debugging. As this is a costly operation, I don't want to do it in a release build. Right now I'm using functions like:

pub fn debug_panic_on_errors() {
    if cfg!(debug_assertions) {
        get_errors().unwrap();
    }
}

Am I correct in assuming that this method will always be optimized away completely? Is there a better, more future-proof way?

Answer 1

In release mode the function will be expanded to if false { … } which is very trivial to optimize away, so yes you could just use it as-is.

---

If you are being paranoid you could #[cfg] two functions like

#[cfg(debug_assertions)]
pub fn debug_panic_on_errors() { 
    get_errors().unwrap();
}

#[cfg(not(debug_assertions))]
pub fn debug_panic_on_errors() {
}

so that the outcome is chosen during parsing, to ensure we don't rely on the optimizer. But I don't really recommend this...