Macro warn_once 

macro_rules! warn_once {
    ($($arg:tt)*) => { ... };
}

Logs a message at the warn level exactly once per callsite.

The first invocation logs the message; all subsequent calls are silently dropped.

Example

use log_debounce::warn_once;

// Logs only the first time this line is reached
warn_once!("Deprecated configuration detected");