date.exe -u argument doesn't work.

[hellishvictor]

Hi, I think I've found a bug using the -u argument with date.exe. When is used with the GnuWin32 version it shows:
date.exe -u -d "@1715372666" +"%F, %T %Z%z"
2024-05-10, 20:24:26 UTC+0000

And when is not used:
date.exe -d "@1715372666" +"%F, %T %Z%z"
2024-05-10, 21:24:26 Hora de verano GMT+0100

But with coreutils, with or without the -u, it always shows the same time:
coreutils date -d "@1715372666" +"%F, %T %Z%z"
2024-05-10, 20:24:26 +01:00+0100
Here without the -u should be one hour more (21:24:26), and when used it should show +0000.

Cheers.

[DaveKram]

I decided to take a look at this - it seems like the following logic needs to be updated:

coreutils/src/uu/date/src/date.rs

Lines 214 to 246 in 8cac375

	let now: DateTime<FixedOffset> = if settings.utc {
	let now = Utc::now();
	now.with_timezone(&now.offset().fix())
	} else {
	let now = Local::now();
	now.with_timezone(now.offset())
	};
	// Iterate over all dates - whether it's a single date or a file.
	let dates: Box<dyn Iterator<Item = _>> = match settings.date_source {
	DateSource::Custom(ref input) => {
	let date = parse_date(input.clone());
	let iter = std::iter::once(date);
	Box::new(iter)
	}
	DateSource::Human(relative_time) => {
	// Get the current DateTime<FixedOffset> for things like "1 year ago"
	let current_time = DateTime::<FixedOffset>::from(Local::now());
	// double check the result is overflow or not of the current_time + relative_time
	// it may cause a panic of chrono::datetime::DateTime add
	match current_time.checked_add_signed(relative_time) {
	Some(date) => {
	let iter = std::iter::once(Ok(date));
	Box::new(iter)
	}
	None => {
	return Err(USimpleError::new(
	1,
	format!("invalid date {}", relative_time),
	));
	}
	}
	}

The math up to this point is still using Local::now() (thus current_time still being a Local::now()). I'm thinking that the return value down below should use the now variable's offset() (since that takes into consideration UTC). I.E something like this:

let iter = std::iter::once(Ok(date.with_timezone(now.offset())));

Which changes the string representation of the date to be offset by now, which is based off of whether the -u UTC flag is set or not.

Would like someone to check this (since is my first look at the repo) - can make a PR if is accurate.

Edit: Probably also would need a new test added, since cargo test date passes as is currently.