HE calendar formats day of the week incorrectly

[IdoLeshkowitz]

Hey,
I'm working on the main branch and I've noticed an issue with formatting the day of the week on he-IL calendar.
to reproduce -

MyApp.Cldr.put_locale("HE")
{:ok, MyApp.Cldr.Locale.new!("he-IL")}
{:ok, today} = MyApp.Cldr.Calendar.localize(Date.utc_today())
{:ok, ~D[2025-01-29 Cldr.Calendar.IL]}
beginning_of_week = Date.beginning_of_week(today)
~D[2025-01-26 Cldr.Calendar.IL]
Calendar.strftime(beginning_of_week, "%a")
"Mon"

You can see that the it returns a correct date for the beginning of the week (2025-01-26), but when formatting the date and extracting day of the week it returns the wrong day (Monday instead of Sunday). Same happens when formatting with Cldr.Calendar.localize

[kipcole9]

This may be similar to the rather lengthy discussion on this topic in which the day of the week is now more clearly ordinal (nth day of the week) not cardinal (a particular day).

Days of the week are ordinal, not cardinal

# This returns 1 because its the first day of the week for Cldr.Calendar.IL
iex> Date.day_of_week ~D[2025-01-26 Cldr.Calendar.IL]
1

# This returns 7 meaning Sunday, because we force the first day of the week
# to be Monday.
iex> Date.day_of_week ~D[2025-01-26 Cldr.Calendar.IL], :monday
7

There is updated documentation for Calendar.day_of_week/2 coming for Elixir 1.18 that should help clarify this topic.

Using MyApp.Cldr.Calendar.strftime_options!/0

There is a way to force options to be returned in a calendar specific way using MyApp.Cldr.Calendar.strftime_options!/0 which can be used with Calendar.strftime/3. But it also has the same bug (a bug since the last update to ex_cldr_calendars that was published to resolve the conversation in the linked PR).

# Needs fixing - will do ASAP. This should be the preferred way to format localized calendars
# using `Calendar.strftime/2`.
iex> Calendar.strftime ~D[2025-01-26 Cldr.Calendar.IL], "%a", MyApp.Cldr.Calendar.strftime_options!()
"Mon"

Using ex_cldr_dates_times returns the correct result

The correct day of the week is returned if you use Cldr.Date.to_string/2, for example:

iex> Cldr.Date.to_string ~D[2025-01-26 Cldr.Calendar.IL], format: "E"
{:ok, "Sun"}

Next steps

1. See if this is considered a bug in Calendar.strftime/3 or not.
2. Fix MyApp.Cldr.Calendar.strftime_options!/0 to return the right value (will do in the next 24 hours). For any localised calendars this is the appropriate strategy for formatting anyway.

[kipcole9]

I've pushed a couple of commits that should fix this issue. For example:

iex> {:ok, calendar} = Cldr.Calendar.calendar_from_locale("he")
iex> {:ok, date} = Date.new(2025, 1, 26, calendar)
iex> Calendar.strftime date, "%a",
...>   MyApp.Cldr.Calendar.strftime_options!(calendar: calendar, locale: "en")
"Sun"

I need to add more tests but I think this is close to being ready to ship. Would you consider giving this a test in your environment?

[kipcole9]

Note the requirement to use MyApp.Cldr.Calendar.strftime_options!/1, and to pass the calendar in to ensure the right results. The locale is optional and is derived from Cldr.get_locale/0 if not specified.

[kipcole9]

BTW, I'm more than happy to try to implement the native Hebrew calendar as well. I don't have the domain expertise and would welcome some collaboration on that if you're up for it.

[IdoLeshkowitz]

I've pushed a couple of commits that should fix this issue. For example:

iex> {:ok, calendar} = Cldr.Calendar.calendar_from_locale("he")
iex> {:ok, date} = Date.new(2025, 1, 26, calendar)
iex> Calendar.strftime date, "%a",
...> MyApp.Cldr.Calendar.strftime_options!(calendar: calendar, locale: "en")
"Sun"
I need to add more tests but I think this is close to being ready to ship. Would you consider giving this a test in your environment?

sure 💥

[IdoLeshkowitz]

BTW, I'm more than happy to try to implement the native Hebrew calendar as well. I don't have the domain expertise and would welcome some collaboration on that if you're up for it.

I would love to, I will try and dig in on the weekend, I would note that the hebrew calendar is barely used in Israel 😅 its mostly used for religious stuff, most people dont even know how to read it and use the classic Gregorian.

[IdoLeshkowitz]

I've pushed a couple of commits that should fix this issue. For example:

iex> {:ok, calendar} = Cldr.Calendar.calendar_from_locale("he")
iex> {:ok, date} = Date.new(2025, 1, 26, calendar)
iex> Calendar.strftime date, "%a",
...> MyApp.Cldr.Calendar.strftime_options!(calendar: calendar, locale: "en")
"Sun"
I need to add more tests but I think this is close to being ready to ship. Would you consider giving this a test in your environment?

Calendar.strftime works! thanks so much for the fix, BTW I've noticed that on my environment Cldr.Calendar.Date.to_string still returns monday, what could possibly be the reason? (I'm on the main branch updated with latest commits)

Cldr.Date.to_string ~D[2025-01-26 Cldr.Calendar.IL], format: "E"
{:ok, "Mon"}

[kipcole9]

Maybe your version of ex_cldr_calendars needs updating? Thats the lib that actually does the calculation. Latest version is 1.26.4. I just revalidated that is returns the correct day on my system with that version:

iex> Cldr.Date.to_string ~D[2025-01-26 Cldr.Calendar.IL], format: "E"
{:ok, "Sun"}

[kipcole9]

I would love to, I will try and dig in on the weekend, I would note that the hebrew calendar is barely used in Israel 😅 its mostly used for religious stuff, most people dont even know how to read it and use the classic Gregorian.

I can do most of the work, but having someone to ask questions of would be great - I lack the cultural and religious context so terminology definitely confuses me!

[kipcole9]

Oh you are right, on ex_cldr_calendars main branch is does return an incorrect result!

iex> Cldr.Date.to_string ~D[2025-01-26 Cldr.Calendar.IL], format: "E"
{:ok, "Mon"}

I'm on it (and adding a test)

[IdoLeshkowitz]

I would love to, I will try and dig in on the weekend, I would note that the hebrew calendar is barely used in Israel 😅 its mostly used for religious stuff, most people dont even know how to read it and use the classic Gregorian.

I can do most of the work, but having someone to ask questions of would be great - I lack the cultural and religious context so terminology definitely confuses me!

cool! I'll reach out in slack 🤙

[IdoLeshkowitz]

Oh you are right, on ex_cldr_calendars main branch is does return an incorrect result!

iex> Cldr.Date.to_string ~D[2025-01-26 Cldr.Calendar.IL], format: "E"
{:ok, "Mon"}
I'm on it (and adding a test)

awesome! 🙌

[kipcole9]

OK, I've pushed changes to make sure calendar localisations work for calendars where the start of the week isn't Monday and the start of the year isn't January. Tests also added.

I'm stretching your patience I know, but would you mind testing from main branch one more time?

[IdoLeshkowitz]

OK, I've pushed changes to make sure calendar localisations work for calendars where the start of the week isn't Monday and the start of the year isn't January. Tests also added.

I'm stretching your patience I know, but would you mind testing from main branch one more time?

works perfectly 💪 thanks again for your help I appreciate it so much 🙏

[kipcole9]

Great to hear! I'll publish an update to hex in the next hour or so. Thanks for the collaboration.