Avoid JSON serializing Float::INFINITY

[jhawthorn]

This works fine under the default JSON library (it ends up being NULL), but it errors under OJ.

Fixes #2486

[hhff]

LGTM but i'd guess that in_stock? and potentially is_backorderable? also doesn't need to be serialized when we're not tracking inventory. Just a thought!

[jhawthorn]

LGTM but i'd guess that in_stock? and potentially is_backorderable? also doesn't need to be serialized when we're not tracking inventory. Just a thought!

I've spent some time thinking about this. You're right that it's confusing to have values that should basically be ignored when track_inventory is off. I think in stock should probably keep in_stock even if we were to hide backorderable, as we do in most places consider track_inventory=false to imply in_stock.

Related to this is #2522, where we are considering adding another attribute/scope to represent (in_stock || backorderable || !track_inventory).

For now, at least, I think we should keep all of these fields in for compatibility.

[joshhepworth]

I just ran into this issue as well, and actually had to address this in the Products API as well due to this line: https://github.com/solidusio/solidus/blob/master/api/app/helpers/spree/api/api_helpers.rb#L54

The because the Spree::Product#any_variants_not_track_inventory? method is private, I ended up with this in _product.json.jbuilder, which is not pretty for a few reasons:

  json.(product, *@product_attributes - [:total_on_hand])

  json.total_on_hand(product.total_on_hand.to_f.infinite? == 1 ? nil : product.total_on_hand)

I'm not sure if this is acceptable, or if you'd rather have a solution that cleaned this up a little more extensively. I'm also not sure if the product_attributes helper ends up touching other endpoints as well.