feat: add erythritol as a nutrient

[stephanegigandet]

This PR adds erythritol as a nutrient, and adds tests for the nutrients to energy coherency test.

Fixes #7837

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[alexgarel]

Perfect !

[CharlesNepote]

Great!

You modified the test but not the algorithm to compute energy: don't you have to subtract erythritol from polyols? Do you intend to do it after?

[CharlesNepote]

--added-sugars: as I understand it will be displayed as a sub-category of sugars, isn't it? (Which is good I think.)

Does it have an impact on its name in the CSV export?

[stephanegigandet]

yes, that makes added sugars a sub category of sugars (as displayed in USDA labels)

[stephanegigandet]

You modified the test but not the algorithm to compute energy: don't you have to subtract erythritol from polyols? Do you intend to do it after?

I had done it before in fact, but it didn't work because erythritol was not in the nutrients taxonomy:

https://github.com/openfoodfacts/openfoodfacts-server/blob/main/lib/ProductOpener/DataQualityFood.pm#L527

my %energy_from_nutrients = (
	europe => {
		carbohydrates_minus_polyols => {kj => 17, kcal => 4},
		polyols_minus_erythritol => {kj => 10, kcal => 2.4},
		proteins => {kj => 17, kcal => 4},
		fat => {kj => 37, kcal => 9},
		salatrim => {kj => 25, kcal => 6},    # no corresponding nutrients in nutrient tables?
		alcohol => {kj => 29, kcal => 7},
		organic_acids => {kj => 13, kcal => 3},    # no corresponding nutrients in nutrient tables?
		fiber => {kj => 8, kcal => 2},
		erythritol => {kj => 0, kcal => 0},    # no corresponding nutrients in nutrient tables?
	},
);

I'll remove the comment about no corresponding nutrients

[CharlesNepote]

I had done it before in fact, but it didn't work because erythritol was not in the nutrients taxonomy:

Yes I remember now, thanks a lot!