An implementation of MF2 with column-first selection

[eemeli]

Following yesterday's discussion, I've updated my JS Intl.MessageFormat polyfill to provide two up-to-date implementations with the following selection method alternatives:

# first-match
npm install messageformat@4.0.0-3

# column-first
npm install messageformat@4.0.0-3.cf

The change in getting from the former to the latter is effectively commit f5d1bba, which changes the message value selection method from matchSelectKey(key: string): boolean to selectKey(keys: Set<string>): string | null. The actual selection algorithm is found in the getPattern() function in message-value/resolved-message.ts.

To play around with this locally, run one of the above shell commands and then create a new file test.mjs with these contents:

import { MessageFormat } from "messageformat";

function test(msg, args) {
  const mf = new MessageFormat(msg, "en-US");
  const res = mf.resolveMessage(args);
  console.log(res.toString());
}

test(`
  let $x = {|1| :number}
  let $y = {|1| :number minimumFractionDigits=2}
  match {$x} {$y}
  when one one {{$x} is one, {$y} is one}
  when one 1 {{$x} is one, {$y} is exact}
  when 1 one {{$x} is exact, {$y} is one}
  when 1 1 {{$x} is exact, {$y} is exact}
  when * * {fallthrough}
`);

then run node test.mjs to observe the results. With 4.0.0-3, the when one 1 variant will be selected, while 4.0.0-3.cf will select when 1 1. You may run the corresponding npm install command to switch from one to another.

To experiment with more complex rules while staying in English, the :number function supports the type=ordinal option to perform ordinal rather than cardinal selection.

CC @aphillips, @stasm, @mihnita

[macchiati]

Good idea to use ordinals in English (quite similar to Slavic cardinals)

[mihnita]

I've merged the Java implementation for best match selection.
It is in the experimental branch, in /experiments/mihnita/mf2_bestmatch

---

It is a copy of the existing ICU4J implementation, with the classes moved to a different package to avoid conflicts.
Is still uses ICU to format dates, times, numbers, get plural rules, etc.

It is maven, so all you need to do is mvn package

---

I've added a dedicated test file (Mf2BestMatchTest),
where the cases are sorted "the worst way possible" (* first, then one then =1).

And has an ordinal example:

match {$count :selectordinal}
 when * {The {$count}th place}
 when one {The {$count}st place}
 when two {The {$count}nd place}
 when few {The {$count}rd place}
 when 1 {Gold medal}
 when 2 {Silver medal}
 when 3 {Bronze medal}

---

The commits are cleanly separated to show the progress, from an empty maven project to the final version.
The only relevant commit is b06bba2, that is the commit changing from first match to best match.

The changes needed are really minimal.

[eemeli]

Could you adjust the test suite to not depend on the system defaults? I'm getting quite a few errors that appear to be due to using en-FI as my system locale, and in a different timezone than expected.

[mihnita]

Thank you, good point.
Done.
M.

[eemeli]

Following #372, I've merged this into the JS polyfill in messageformat/messageformat#395.