Duration fmt::Debug impl doesn't honor alignment

[hawkw]

It appears that the fmt::Debug implementation for std::time::Duration ignores alignment/width specifiers.

For example, see this playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=d5daccbe4b2e510f4dcee8d85e421b47

I tried this code:

Formatting a Duration with alignment/width specifiers (with a f64 for comparison).

fn main() {
    use std::time::Duration;
    let some_duration = Duration::from_millis(100) + Duration::from_micros(555);
    println!(" left aligned `Duration` = {:>20?} foo", some_duration);
    println!(" left aligned `f64`      = {:>20?} foo", 100.555f64);
    println!("right aligned `Duration` = {:<20?} foo", some_duration);
    println!("right aligned `f64`      = {:<20?} foo", 100.555f64)
}

I expected to see this happen:

The durations should be padded to fill the specified width, and aligned based on the alignment specifier (identically to the f64 value. I would expect to see output that looks like this:

 left aligned `Duration` =            100.555ms foo
 left aligned `f64`      =              100.555 foo
right aligned `Duration` = 100.555ms            foo
right aligned `f64`      = 100.555              foo

Instead, this happened:

The Durations are not padded to the specified width, and are not aligned based on the format specifier. The output looks like this:

 left aligned `Duration` = 100.555ms foo
 left aligned `f64`      =              100.555 foo
right aligned `Duration` = 100.555ms foo
right aligned `f64`      = 100.555              foo

Meta

rustc --version --verbose:
On my machine, the version is:

rustc 1.53.0 (53cb7b09b 2021-06-17)
binary: rustc
commit-hash: 53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b
commit-date: 2021-06-17
host: x86_64-unknown-linux-gnu
release: 1.53.0
LLVM version: 12.0.1

In the playground this also occurs on stable 1.54.0, and on 1.56.0-nightly (2021-08-14 8007b506ac5da629f223). Looking at the git blame, though, it looks like Duration's Debug impl has had this behavior since 9eeb13f (prior to that commit, it simply derived Debug).

[hawkw]

I'd be happy to work on a PR to change this behavior, provided it's agreed that we would want to honor fill/width/alignment here?

[Friz64]

Is this related to #87905?

[michiel-de-muynck]

Fixed by #88999.