Fill/Alignment is ignored for Debug

[stepancheg]

Code:

println!("<<<{:>10}>>>", "abcd");
println!("<<<{:>10?}>>>", "abcd");

outputs:

<<<      abcd>>>
<<<"abcd">>>

First version is padded, second is not.

Debug output should be padded, or it should be a compilation error at least.

Playpen

[alexcrichton]

Various formatting flags like this are ignored by almost all formatting implementations, so I don't think it's possible to yield a compilation error. That being said there's a case that perhaps the standard Debug implementations should respect this, as well as the debug builders.

[Mark-Simulacrum]

Closing in favor of #30164.