Extend time skeleton symbol support (add "j")

[batjaa]

TLDR: I'm trying to add support for time skeleton pattern "j" but the locale is required to parse it. Would passing down the locale as part of ParserOptions a feasible idea? If not, what would be a good way to pass the locale to @formatjs/icu-messageformat-parser/parser()?

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Locale aware time skeleton patterns are very convenient and are encouraged to be used when formatting time. e.g. instead of trying to figure out if it's "h" or "H" you can simply pass in "j" and the formatter can figure out what the locale prefers. But as we know support for all date/time skeleton symbols are not complete.

I'm trying to figure out how to add support for "j". According to the spec "j", "J" and "C" are supposed to be converted to date/time patterns before processing (according to the spec).

j → one of {H, k, h, K}; C → one of {a, b, B}

I've a prototype method that pre-processes the skeleton pattern and returns the best matching date pattern when a locale is provided. It makes sense to keep this method in @formatjs/icu-skeleton-parser or @formatjs/icu-messageformat-parser. But there isn't an easy way to pass the locale to these parsers.

The current solution I've come up so far is to pass it down as part of the options prop — I don't like this approach myself that much:

packages/intl-messageformat/src/core.ts

// ln: 133
        this.ast = IntlMessageFormat.__parse(message, {
         ignoreTag: opts?.ignoreTag,
        locale: new Intl.Locale(locales[0]), // something like this
})

packages/icu-messageformat-parser/parser.ts

// store locale from option as a private property
...
// ln: 766
            let datePattern = skeleton;

            if (this.locale) {
              datePattern = getBestPattern(skeleton, this.locale);
            }

            const style: DateTimeSkeleton = {
              type: SKELETON_TYPE.dateTime,
              pattern: datePattern,
              location: styleAndLocation.styleLocation,
              parsedOptions: this.shouldParseSkeletons
                ? parseDateTimeSkeleton(datePattern)
                : {},
            }

[longlho]

granted we convert from ICU skeleton to ECMA402 options which, under the hood does best match skeleton matching anw. If I'm understanding this correctly the only difference between j and h,H,k,K is hourCycle, which if you leave as undefined would best match on that?

[longlho]

maybe I misunderstood. Do you have an example?

[batjaa]

Yeah, created this draft. I just need a better way to pass the locale down to the Parser.

[longlho]

ah kk I see. I think that's reasonable. If you can warn if j is being used and locale is not passed in that'd be great. We use the parser to pre-parse AST as well

[batjaa]

Yeah, cool, I'll revise the PR and submit it.

[batjaa]

Just heads up, I found out that locale.hourCycle and locale.hourCycles are not very reliable at the moment and perhaps need to unpack CLDR data to achieve this. Investigating that as time allows me.

[batjaa]

I'm not able mark this discussion as answered :\