Macro log_debug 

macro_rules! log_debug {
    () => { ... };
    ($f: literal) => { ... };
    ($f: expr) => { ... };
    ($f: literal, $( $a:expr ),* ) => { ... };
}

A convenience macro for debug logging using [log_debug] function.

• When called without arguments, will print the current file name and line number.
• When called with a string, just prints that string.
• When called with multiple arguments, prints a string produced by [format!].