Add translatePlural filter

[pswai]

Issue #104

This adds translatePlural filter with syntax

{{'One rock' | translatePlural:rocks.length:'{} rocks'}}

This is a bit different with what @rubenv suggested

{{"1 car" | translatePlural:n:"$count cars"}}
{{"1 car" | translatePlural:n:"$count cars":"domain"}} // With a domain

1. Use {} instead of $count. That's because the probability of collision of $count is higher than {} I think. Matching {} is also much easier.
2. Domain is not supported as I'm not too familiar with it. It can be added later on if somebody needs it.

[rubenv]

Why not use {{$count}}? Does that get substituted in the string?

Having two different syntaxes is really troublesome: it would given an error if you have this situation:

{{"1 car" | translatePlural:n:"$count cars"}}

<div translate translate-n="n" translate-plural="{{$count}} cars">1 car</div>

Not the mismatching values for the plural string. There's no way we can handle that.

This cannot go in unless we find a way to make this work:

{{"1 car" | translatePlural:n:"{{$count}} cars"}}

[rubenv]

I just noticed that I made the mistake of putting it wrong in #104. Sorry for that.

[rubenv]

No need to have this assertion.

[rubenv]

Apart from the points above: excellent work! If we can fix the things above, I see no reason not to merge this.

[pswai]

{{$count}} is not used because $parse seems to prohibit nested delimiters. Expressions like

{{'1 apple' | translatePlural:n:'{{$count}} apples'}}

result in parse error. I think that's why ngPluralize is using {} as their count token. Do you know any way to get around this?

[rubenv]

{{$count}} is not used because $parse seems to prohibit nested delimiters.
Expressions like {{'1 apple' | translatePlural:n:'{{$count}} apples'}} result in parse error.

Ok, that is a problem. Guess we'll have to take that constraint as a given.

But it's not just an option to use a new interpolation syntax as-such. Consider the case where we opt to use $count in translatePlural filters:

{{'1 apple' | translatePlural:n:'$count apples'}}

In combination with a different occurrence:

<span translate translate-n="n" translate-plural="{{$count}} apples">1 apple</span>

This would fail during message extraction since we have two different plural strings for 1 apple:

• $count apples
• {{$count}} apples

One option (and this might be crazy-talk) is to support $count in filters (as in the example above). This would be a special case, with two added hacks to make it work:

1. The first step in the filter code would be to replace $count by {{$count}}, such that normal interpolation works.
2. The extractor is modified to recognize $count in translatePlural filters and does a similar replace. That way we end up with only one plural string in the .pot: {{$count}} apples.

I'm inclined towards $count rather than {}, as it's more similar to {{$count}} and more recognisable as a variable.

Something to think about.

Adding @gabegorelick to CC, he might have input too.

[gabegorelick]

Yeah, $count makes more sense.

[gabegorelick]

We may want to do something like rubenv/angular-gettext-tools#63 (comment) instead.

[gabegorelick]

FYI, you want to use $interpolate instead of $parse. That solves the {{}} issue.

Nevermind. $compile parses {{}} inside string literals.