Update FluentNumber to use ICU4X

[juliancoffee]

Update (from @gregtatum): This bug is now about about using ICU4X's number formatter to back FluentNumber.

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It seems that fluent-rs can parse options for numbers, but not use them.
Looking at FluentNumber::as_string(), the only option that gets used is minimum fraction digits.

    pub fn as_string(&self) -> Cow<'static, str> {
        let mut val = self.value.to_string();
        if let Some(minfd) = self.options.minimum_fraction_digits {
            if let Some(pos) = val.find('.') {
                let frac_num = val.len() - pos - 1;
                let missing = if frac_num > minfd {
                    0
                } else {
                    minfd - frac_num
                };
                val = format!("{}{}", val, "0".repeat(missing));
            } else {
                val = format!("{}.{}", val, "0".repeat(minfd));
            }
        }
        val.into()
    }

So, things to implement:

• Percent formatting
• Currency formatting
• Decimal formatting (implicitly assumed, I guess)
• use_grouping
• minimum_integer_digits
• minimum_fraction_digits
• maximum_fraction_digits
• minimum_significant_digits
• maximum_significant_digits

[juliancoffee]

@zbraniecki
I thought about implementing percentage formatting, but I'm a bit worried about language-dependent formatting, do you have any advice on how to do it?

[zbraniecki]

I'd wait for ICU4X NumberFormatter, we have scaffolding for it in https://unicode-org.github.io/icu4x-docs/doc/fixed_decimal/index.html for some aspects, and unicode-org/icu4x#1441 for others.

Maybe you'd like to help with that? :)

[juliancoffee]

I'd wait for ICU4X NumberFormatter, we have scaffolding for it in https://unicode-org.github.io/icu4x-docs/doc/fixed_decimal/index.html for some aspects, and unicode-org/icu4x#1441 for others.

Maybe you'd like to help with that? :)

Yeah, I was looking at that a bit. What are the approximate steps for working on that?

[zbraniecki]

What are the approximate steps for working on that?

You can go to issue #1441 and say you'd like to take it and ask for mentorship. Someone from our team will mentor you through that.

If you prefer some other feature of Number Formatter you can ask here unicode-org/icu4x#275 and we'll help you carve out correct API to work on.

The concept in ICU4X is to divide what JS knows as NumberFormat into a tree of more specific and smaller formatters.

[gregtatum]

In Firefox we are using ICU4C to do this, but the examples in fluent-rs should be backed by ICU4X's number formatter. I'll update this issue to say as much.

[alerque]

I believe this work is already in progress and should be addressed as part of #335. Also of note #303 along the way. Also relevant is #353 which touches on these implementations.