Fill/alignment overrides # specifier in format strings

[ketsuban]

Here's a sample program.

fn main() {
    let foo: u8 = 0xA;
    println!("{:b}", foo);
    println!("{:>08b}", foo);
    println!("{:#b}", foo);
    println!("{:#>08b}", foo); // <--
}

I expected this output.

1010
00001010
0b1010
0b00001010

I got this output.

1010
00001010
0b1010
00001010

[hirschenberger]

Your format string is wrong. The syntax from the doc is:

format_spec := [[fill]align][sign]['#']['0'][width]['.' precision][type]

So the formatstring should be {:>#08b} and this works https://is.gd/Wpxf90 in your example, the # is the fill character before the alignment. Also {:#>#8b} works as expected.

But in my opinion it should fail to compile.

[Mark-Simulacrum]

Yes, the format syntax does appear to be incorrect here, and should be {:>#010b} to produce the result you expected.