    macro_rules! println {
        ($($arg:tt)*) => ({
            $crate::io::_print($crate::format_args_nl!($($arg)*));
        })
    }
    #[rustc_builtin_macro]
    #[macro_export]
    macro_rules! format_args {}
    #[rustc_builtin_macro]
    #[macro_export]
    macro_rules! const_format_args {}
    #[rustc_builtin_macro]
    #[macro_export]
    macro_rules! format_args_nl {}

    mod panic {
        pub macro panic_2015 {
            () => (
                $crate::panicking::panic("explicit panic")
            ),
            ($msg:literal $(,)?) => (
                $crate::panicking::panic($msg)
            ),
            // Use `panic_str` instead of `panic_display::<&str>` for non_fmt_panic lint.
            ($msg:expr $(,)?) => (
                $crate::panicking::panic_str($msg)
            ),
            // Special-case the single-argument case for const_panic.
            ("{}", $arg:expr $(,)?) => (
                $crate::panicking::panic_display(&$arg)
            ),
            ($fmt:expr, $($arg:tt)+) => (
                $crate::panicking::panic_fmt($crate::const_format_args!($fmt, $($arg)+))
            ),
        }
    }

    #[rustc_builtin_macro(std_panic)]
    #[macro_export]
    macro_rules! panic {}
    #[rustc_builtin_macro]
    macro_rules! assert {}
    #[rustc_builtin_macro]
    macro_rules! asm {}
    #[rustc_builtin_macro]
    macro_rules! concat {}

    macro_rules! toho {
        () => ($crate::panic!("not yet implemented"));
        ($($arg:tt)+) => ($crate::panic!("not yet implemented: {}", $crate::format_args!($($arg)+)));
    }

    fn main() {
        let a = '\n';
        let a = '\t';
        let a = '\e'; // invalid escape
        let a = 'e';
        let a = ' ';
        let a = '\u{48}';
        let a = '\u{4823}';
        let a = '\x65';
        let a = '\x00';

        let a = b'\xFF';

        println!("Hello {{Hello}}");
        // from https://doc.rust-lang.org/std/fmt/index.html
        println!("Hello");                 // => "Hello"
        println!("Hello, {}!", "world");   // => "Hello, world!"
        println!("The number is {}", 1);   // => "The number is 1"
        println!("{:?}", (3, 4));          // => "(3, 4)"
        println!("{value}", value=4);      // => "4"
        println!("{} {}", 1, 2);           // => "1 2"
        println!("{:04}", 42);             // => "0042" with leading zerosV
        println!("{1} {} {0} {}", 1, 2);   // => "2 1 1 2"
        println!("{argument}", argument = "test");   // => "test"
        println!("{name} {}", 1, name = 2);          // => "2 1"
        println!("{a} {c} {b}", a="a", b='b', c=3);  // => "a 3 b"
        println!("{{{}}}", 2);                       // => "{2}"
        println!("Hello {:5}!", "x");
        println!("Hello {:1$}!", "x", 5);
        println!("Hello {1:0$}!", 5, "x");
        println!("Hello {:width$}!", "x", width = 5);
        println!("Hello {:<5}!", "x");
        println!("Hello {:-<5}!", "x");
        println!("Hello {:^5}!", "x");
        println!("Hello {:>5}!", "x");
        println!("Hello {:+}!", 5);
        println!("{:#x}!", 27);
        println!("Hello {:05}!", 5);
        println!("Hello {:05}!", -5);
        println!("{:#010x}!", 27);
        println!("Hello {0} is {1:.5}", "x", 0.01);
        println!("Hello {1} is {2:.0$}", 5, "x", 0.01);
        println!("Hello {0} is {2:.1$}", "x", 5, 0.01);
        println!("Hello {} is {:.*}",    "x", 5, 0.01);
        println!("Hello {} is {2:.*}",   "x", 5, 0.01);
        println!("Hello {} is {number:.prec$}", "x", prec = 5, number = 0.01);
        println!("{}, `{name:.*}` has 3 fractional digits", "Hello", 3, name=1234.56);
        println!("{}, `{name:.*}` has 3 characters", "Hello", 3, name="1234.56");
        println!("{}, `{name:>8.*}` has 3 right-aligned characters", "Hello", 3, name="1234.56");

        let _ = "{}"
        let _ = "{{}}";

        println!("Hello {{}}");
        println!("{{ Hello");
        println!("Hello }}");
        println!("{{Hello}}");
        println!("{{ Hello }}");
        println!("{{Hello }}");
        println!("{{ Hello}}");

        println!(r"Hello, {}!", "world");

        // escape sequences
        println!("Hello\nWorld");
        println!("\u{48}\x65\x6C\x6C\x6F World");

        let _ = "\x28\x28\x00\x63\xFF\u{FF}\n"; // invalid non-UTF8 escape sequences
        let _ = b"\x28\x28\x00\x63\xFF\u{FF}\n"; // valid bytes, invalid unicodes
        let _ = c"\u{FF}\xFF"; // valid bytes, valid unicodes
        let backslash = r"\\";

        println!("{\x41}", A = 92);
        println!("{ничоси}", ничоси = 92);

        println!("{:x?} {} ", thingy, n2);
        panic!("{}", 0);
        panic!("more {}", 1);
        assert!(true, "{}", 1);
        assert!(true, "{} asdasd", 1);
        toho!("{}fmt", 0);
        asm!("mov eax, {0}");
        format_args!(concat!("{}"), "{}");
        format_args!("{} {} {} {} {} {}", backslash, format_args!("{}", 0), foo, "bar", toho!(), backslash);
    }