Date Interval formatting crossing a year boundary

[matt-glover]

Hi,

First off thanks for the work on this great library!

I have some code to display date intervals using this library and leveraging the short format with the month_and_day style. I discovered that this returns an error whenever the date range crosses a year boundary. For example:

iex(1)> Cldr.Date.Interval.to_string(~D[2023-12-31], ~D[2024-01-02], MyApp.Cldr, [format: :short, style: :month_and_day])
{:error,
 {Cldr.DateTime.UnresolvedFormat,
  "The interval format :y is invalid. Valid formats are [:short, :long, :medium] or an interval format string."}}

I can see why/how this triggers (explained below). But my core question is whether I should treat this as a special case and handle it myself using a different format/custom logic or if I should consider this a bug somewhere in the Elixir CLDR stack and try to issue a patch.

I dug into the formatting rules and saw that short format and month_and_day style give me Md. In the default "en" locale with a default Gregorian calendar I get Md: %{d: ["M/d – ", "M/d"], M: ["M/d – ", "M/d"]},. The greatest difference check for date intervals spits out y (year) as the difference here and then obviously lacking a y option in the Md map it tells me the interval format is invalid.

I hoped to stick with the shortcut options like short and long to get support out-of-the-box for various locales. Seems like that might work okay here if I ditched the style parameter?

I'm a little out of my depth so I paused here before identifying whether the Md mapping is from the Unicode CLDR project itself vs something in one of the suite of Elixir libraries involved. Any advice is appreciated.

[kipcole9]

Matt, thanks for the kind words. Time is hard! I understand what you're trying to do. Let me think on it a bit today (UTC+11) and see what can be done.

[kipcole9]

Matt, I've pushed a commit which I believe does what you expect. Already the code will fallback to "greatest difference :year" from the greatest difference month and day if those formats don't exist. So it's reasonable that greatest difference :year should also try month and day formats if a year format doesn't exist.

Would you considering configuring ex_cldr_dates_times from GitHub and let me know if it works for your requirements?

With this commit the code now does the following:

  defp greatest_difference_format(format, requested_format, requested_style, :y = difference) do
    resolved_format = Map.get(format, difference) || Map.get(format, :M) || Map.get(format, :d) || :error

    case resolved_format do
      :error -> {:error, unavailable_format_error(requested_format, requested_style, difference)}
      success -> {:ok, success}
    end
  end

I also improved the error message if there is no resolvable format (it wasn't a very good one before).

Lastly, I did a proof read of the various Interval modules to make them a bit better.

Let me know if this now works as you expect - and of course re-open if not. I will publish to Hex an update when you say it's ok for you.

[matt-glover]

I’ll take a look Monday (UTC-4) when I get in to work to be sure. But glancing at the PR I’m pretty sure the change is exactly what I need.

[matt-glover]

That change is producing the expected output for me. I had to update various other CLDR dependencies and I'm getting plenty of other test failures I have to work through where we asserted on CLDR output already. But I get those failures with the latest ex_cldr* packages including the latest released version of this package. I suspect my issues are tied to CLDR 43 which we weren't using yet. Seeing a mix of no longer valid formats + changes around the type of space or hyphen/dash/etc being used to delimit things. So I'll be debugging those before I can cut over to this latest version. But the fix looks good to me.

Thanks for all the help!

[kipcole9]

Yes, CLDR 43 did change quite a bit of white space in formats. A pain for updating tests I agree, but a better longer-term outcome.

I've published ex_cldr_dates_times version 2.14.3 with the following changelog entry:

Bug Fixes

• Fix formatting date intervals with :month_and_day style when the last date is in a different year to the first. Thanks to @matt-glover for the report. Closes #40.