为什么 Rust 的 println! 不会发生所有权转移？

let x = String::from("Hello!");
println!("{}", x);
println!("{}", x);

#[macro_export]
#[stable(feature = "rust1", since = "1.0.0")]
#[allow_internal_unstable(print_internals, format_args_nl)]
macro_rules! println {
    () => ($crate::print!("\n"));
    ($($arg:tt)*) => ({
        $crate::io::_print($crate::format_args_nl!($($arg)*));
    })
}
​
#[unstable(
    feature = "format_args_nl",
    issue = "none",
    reason = "`format_args_nl` is only for internal \
              language use and is subject to change"
    )]
#[allow_internal_unstable(fmt_internals)]
#[rustc_builtin_macro]
#[macro_export]
macro_rules! format_args_nl {
    ($fmt:expr) => {{ /* compiler built-in */ }};
    ($fmt:expr, $($args:tt)*) => {{ /* compiler built-in */ }};
}

#![feature(prelude_import)]
#![no_std]
#[prelude_import]
use ::std::prelude::v1::*;
#[macro_use]
extern crate std;
fn main() {
    let x = String::from("Hello!");
    {
        ::std::io::_print(::core::fmt::Arguments::new_v1(&["", "\n"],
                                                         &match (&x,) {
                                                             (arg0,) => [::core::fmt::ArgumentV1::new(arg0,::core::fmt::Display::fmt)],
        }));
    };
}