Description
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).