How to select "glue pattern"?

[FrankYFTang]

Spin off from https://github.com/tc39/ecma402/issues/190

The issue is what part of the specification decide which glue pattern should be used.

@caridy commented on Oct 27, 2017

In most cases, you can get away with transforming a pattern/skeleton into a DateTimeFormat options, specially if you're flexible with the output. E.g.:

var f = {
  weekday: 'long',
  month: 'long',
  day: 'numeric',
  year: 'numeric',
  hour: 'numeric',
  minute: '2-digit',
  second: '2-digit',
  hour12: true,
  timeZoneName: 'long'
};

new Intl.DateTimeFormat('en-US', f).format(Date.now()) "Friday, October 27, 2017, 4:14:53 PM Eastern Daylight Time" Most browsers, today, will add a comma after the year (IE11 does something slightly different) for that set of options. But if you look at the latest ICU library, we see this pattern: "EEEE, MMMM d, y 'at' h:mm:ss a zzzz", which does have an at in between and no coma for en-US.

I wrote some experimental library to try to see if we can help people who want to use patterns/skeleton for convenience, but still preserving the invariants of Intl to do the right thing depending of the locale.

https://github.com/caridy/intl-datetimeformat-pattern

With a library like this, you can get from that pattern/skeleton to the most likely option object that will produce something very similar, but in some cases slightly different due to the those weird differences.

I wonder if someone can actually explain the difference between ICU and browsers for something like the example above?

@jungshik ommented on Nov 22, 2017

@rxaviers is right on 'at' for en-US and CLDR 'glue pattern'. The fact that v8 does not do that is a bug. I thought I had filed a bug on that against v8, but I couldn't find it. Filed https://bugs.chromium.org/p/v8/issues/detail?id=7116 .BTW, this issue is not about 'skeleton' (#189) but about 'pattern'. The former (skeleton) will take a list of fields and field lengths and produce locale-dependent output (order can be shuffled, for instance).

@FrankYFTang wrote:

https://github.com/unicode-cldr/cldr-dates-full/blob/32.0.0/main/en/ca-gregorian.json#L335 show me

"dateTimeFormats": {
"full": "{1} 'at' {0}",
"long": "{1} 'at' {0}",
"medium": "{1}, {0}",
"short": "{1}, {0}",

It is not clear to me which part of the specification determine WHICH glue pattern it should use? Why should it use the "full" one but not the "short" one?

[sffc]

ECMA-402 Recommendation (July 2019): update the spec to reflect ICU behavior.

[FrankYFTang]

@fabalbon - this is related to the issue you talk about the "at" issue.

[sffc]

@FrankYFTang What is the ICU4C behavior?

@zbraniecki What is the ICU4X behavior?

[FrankYFTang]

The ICU glue pattern selection code is in source/i18n/smpdtfmt.cpp#L771

It need a closer look to figure what that code is doing

if ((timeStyle != kNone) && (dateStyle != kNone)) {
...
}

[sffc]

ICU4X uses the date length

https://github.com/unicode-org/icu4x/blob/4242dfbdc7938d036565374e973e37d97b911f41/components/datetime/src/provider/date_time.rs#L213

[sffc]

@ben-allen to update the spec to reflect this behavior (select glue pattern based on date length).

[ben-allen]

This appears to have been fixed by Zibi in 2021 (commit 20c03597d80645f9be5c310820f114b59695beed), which correctly uses the date style to select a pattern from one of [[full]], [[long]], [[medium]], and [[short]]. I've put up PR https://github.com/tc39/ecma402/pull/886 to clarify the wording, which seemed to suggest that the field [[DateTimeFormat]] directly contained the pattern string, rather than a Record containing the pattern strings for each date style:

[ben-allen]

Completed by Zibi in 2021 (commit 20c0359), wording clarification added in #886