Add support for -u-fw and other Unicode extensions that could impact the result

[sffc]

Related: #30, tc39/ecma402#580

If I write

new Intl.Locale("en-u-fw-tue").getWeekInfo()

then I should get that the first day is Tuesday, but it currently ignores the -u-fw.

[FrankYFTang]

This issue, if put into the proposal, would mean we also have to

1. add additional getter "get Intl.Locale.prototype.firstDayOfWeek"
2. in https://tc39.es/ecma402/#sec-intl.locale-internal-slots add "fw" into "The value of the [[RelevantExtensionKeys]]"
3. in Intl.Locale ( tag [ , options ] ) we need to add step to read "firstDayOfWeek" from option and validate the value.

[sffc]

TG2 agreement: https://github.com/tc39/ecma402/blob/master/meetings/notes-2023-05-04.md#add-support-for--u-fw-and-other-unicode-extensions-that-could-impact-the-result

Would like to see this as a normative PR in the July TG1 meeting.

[anba]

If I write

new Intl.Locale("en-u-fw-tue").getWeekInfo()

then I should get that the first day is Tuesday, but it currently ignores the -u-fw.

IIRC you actually get Tuesday starting with ICU 73 (ICU-22226), assuming the input locale is passed as-is to ICU. Addressing #30 should help to clarify how Unicode extension tags are handled.

[FrankYFTang]

So I will add a new getter

1.4.X get Intl.Locale.prototype.firstDayOfWeek

that will return one of the 7 possible values
"sun", "mon", "tue", "wed", "thu", "fri", "sat"

[FrankYFTang]

I think this request surface yet another problem in our current spec
Currently the return value of
Intl.Locale.prototype.getWeekInfo ( )
use integer 1-7 to represent the weekday as specified in
https://tc39.es/proposal-intl-locale-info/#sec-week-info-of-locale

in the firstDay field as a single value and in the weekend as an array (usually 2 values)

But since we are now need to add a getter firstDayOfWeek to return string <<"sun", "mon", "tue", "wed", "thu", "fri", "sat">>
should we also change the getWeekInfo().firstDay to reutrn one of <<"sun", "mon", "tue", "wed", "thu", "fri", "sat">>
and getWeekInfo().weekend to return an arry of string in <<"sun", "mon", "tue", "wed", "thu", "fri", "sat">> instead?

[sffc]

TG2 discussion: https://github.com/tc39/ecma402/blob/master/meetings/notes-2023-06-29.md#intllocale-info-discussion

[FrankYFTang]

This issue and #70 was presented to TC39 in July 12, 2023 meeting and does NOT reach consensus for the proposed changes.

Here are my understanding of the part which reach consensus:
a. No objection of the need to add "fw" to the [[RelevantExtensionKeys]] internal slots in Intl.Locale in order to read "-u-fw-" from the locale identifier.
b. No objection of adding the [[FirstDayOfWeek]] to internal slots in Intl.Locale to keep track the information from a.
c. No objection that the getWeekInfo().firstDay will depends on the value in the [[FirstDayOfWeek]] to internal slots in Intl.Locale
d. No objection to keep the getWeekInfo().firstDay value in the range 1..7 to sync with Temporal.
e. No objection of the need to add a option reading step to get the information to [[FirstDayOfWeek]] in addition to the parsed result from a.
e. No objection of the property name to be read from the option as "firstDayOfWeek".
f. No objection of adding a getter Intl.Locale.prototype.firstDayOfWeek .

But there are disagreement during July 12 TC39 about
I. What should be the possible values that Intl.Locale.prototype.firstDayOfWeek could return.
II What should be the possible values that the option reading of firstDayOfWeek proper should accept.

Option A (as in the current state (July 11, 2023) of PR70)

I. Intl.Locale.prototype.firstDayOfWeek returns: <<undefined, "mon", "tue", "wed", "thu", "fri", "sat", "sun">>
2. {firstDayOfWeek} for new Intl.Locale() accepts: <<undefined, "mon", "tue", "wed", "thu", "fri", "sat", "sun">> Default: undefined

Option B (as mentioned in the TC39)

I. Intl.Locale.prototype.firstDayOfWeek returns: <<undefined, 1, 2, 3, 4, 5, 6, 7>>
2. {firstDayOfWeek} for new Intl.Locale() accepts: <<undefined, "mon", "tue", "wed", "thu", "fri", "sat", "sun", 1, 2, 3, 4, 5, 6, 7>> Default: undefined

Option C (Also mentioned in the TC39)

I. Intl.Locale.prototype.firstDayOfWeek returns: <<undefined, 1, 2, 3, 4, 5, 6, 7>>
2. {firstDayOfWeek} for new Intl.Locale() accepts: <<undefined, "mon", "tue", "wed", "thu", "fri", "sat", "sun", 0, 1, 2, 3, 4, 5, 6, 7>> Default: undefined
where 0, 7, "sun" all repesent Sunday in option reading

Option D

I. Intl.Locale.prototype.firstDayOfWeek returns: <<undefined, 1, 2, 3, 4, 5, 6, 7>>
2. {firstDayOfWeek} for new Intl.Locale() accepts: <<undefined, 1, 2, 3, 4, 5, 6, 7>> Default: undefined

Option E

I. Intl.Locale.prototype.firstDayOfWeek returns: <<undefined, 1, 2, 3, 4, 5, 6, 7>>
2. {firstDayOfWeek} for new Intl.Locale() accepts: <<undefined, 0, 1, 2, 3, 4, 5, 6, 7>> Default: undefined
where 0, and 7 both repesent Sunday in option reading

Option C and Option E consider the fact that Date.prototype.getDay ( ) return 0, but not 7, for Sunday.
See https://tc39.es/ecma262/#sec-date.prototype.getday

[FrankYFTang]

Most people after TG2 2023-09-07 meeting unofficially support Option C

[sffc]

TG2 notes: https://github.com/tc39/ecma402/blob/master/meetings/notes-2023-09-07.md#add-support-for--u-fw-and-other-unicode-extensions-that-could-impact-the-result-68

[FrankYFTang]

This issue is addressed by PR70 after TC39 on 2023-09 which is option C. However, it cause issue in #78 and we now plan to revert from option C

I plan to change the spect to the following:
I. Intl.Locale.prototype.firstDayOfWeek returns: <<undefined, "mon", "tue", "wed", "thu", "fri", "sat", "sun">>
2. {firstDayOfWeek} for new Intl.Locale() accepts: <<undefined, "mon", "tue", "wed", "thu", "fri", "sat", "sun", "0", "1", "2", "3", "4", "5", "6", "7">> Default: undefined
where "0", "7", "sun" all repesent Sunday in option reading

[FrankYFTang]

Propose fix in #79

[FrankYFTang]

I. Intl.Locale.prototype.firstDayOfWeek returns: <<undefined, "mon", "tue", "wed", "thu", "fri", "sat", "sun">>

sorry, this is not right. I need to rework on this. Intl.Locale.prototype.firstDayOfWeek need to return string, but not just that 7 string values.

[FrankYFTang]

#79 and #82 together should address this issue.