Validated plural rules and warn about missing ones

Describe the bug When plural for some language is not translated yet or missing particular form for a given value, the empty string is returned

To Reproduce

import { Trans } from "@lingui/react"

export default function App() {
   return <Plural value={booksNum} other="# books" />
}

Have this extracted with en as a sourceLanguage, then switch to eg. cs.

Expected behavior For booksNum < 5 I would expect that other form will be used as a fallback if one/few is missing in translation. When the booksNum >= 5 it works correctly and result is 5 books even with cs locale.

[tricoder42]

As there’s no easy way to determine “fallback” rule, let’s simply raise validation warning/error when message is missing:

1. In macro, validate plural rules based on linguiConfig.sourceLocale value.
2. In lingui compile --check, validate plural rules for each locale. This will be tricky, as we need to parse message and find plural formatters. On the other hand, we need to parse message anyway to check there’re no syntax errors.
3. In loader, validate plural rules for specific locale (similar to lingui compile --check)
4. Finally in core, show warning about missing plural rule. This is a fallback warning for anyone who doesn’t use macros.

[danielkcz]

But if the product (even free) doesn’t satisfy my needs I have absolute right not to use it, correct?

Sure, and you have also an absolute right to stay silent about it and move along. Screaming “this is bad, I am going away” is useful how exactly? I would recommend you trying to contribute to open-source software to get the feeling of how depressing it is when someone says you are doing a bad job in your spare time.