Code shared from the Rust Playground

playground.rs

macro_rules! fmt_args {
	($($tt:tt)*) => {
	    _fmt_args_!("",; $($tt)*)
	};
}
macro_rules! _fmt_args_ {
	($fmt:expr, $($args:expr,)*; ) => {
	format_args!($fmt $(,$args)*)
	};
	($fmt:expr, $($args:expr,)*; $text:literal $($tail:tt)*) => {
		_fmt_args_!(concat!($fmt, $text), $($args,)*; $($tail)*)
	};
	($fmt:expr, $($args:expr,)*; {$e:expr} $($tail:tt)*) => {
		_fmt_args_!(concat!($fmt, "{}"), $($args,)* $e,; $($tail)*)
	};
	($fmt:expr, $($args:expr,)*; {$e:expr; $($s:tt)*} $($tail:tt)*) => {
		_fmt_args_!(concat!($fmt, "{:", $(stringify!($s),)* "}"), $($args,)* $e,; $($tail)*)
	};
}

fn main() {
    let user = "username";//some_other_module::get_user();
    let port = 80;//some_other_module::get_port();
    let url = fmt_args!("https://"{user}"@www.website.com:"{port}"/").to_string();
    println!("{}", url);
    assert_eq!(url, "https://[email protected]:80/");
}

https://www.reddit.com/r/rust/comments/cxxmi9/comment/eyo6vac