Vegan/Gluten free does not take into account labels

[aleene]

What

The analysis for gluten free and vegan does not take into account any labels. Sometimes the a label can overturn the ingredient analysis

Steps to reproduce the behavior

see: https://de.openfoodfacts.org/product/4014472277088 for a gluten free example
see: https://world.openfoodfacts.org/product/5030756007775/vegan-no-steak-pie-pukka for a vegan example

Expected behaviour

The ingredient analysis should include any label, especially if this is a label by a certification authority. Such a label should overturn the conclusion of the ingredient analysis.

For data quality purposes the (vegan) error could be turned into a warning, just to alert for a possible inconsistency that can be checked and needs to be corrected.

Why

A more correct analysis.

[stephanegigandet]

The current behavior is by design: if we have a no-gluten label, we use it, unless we have ingredients that contradict it...

From Attributes.pm:

	# There may be conflicting information on allergens (e.g. a product that claims to be "gluten-free",
	# but that also says it may contain traces of cereals containing gluten, or that contains an ingredient
	# that usually contains gluten)

	# The algorithm below is designed to be conservative: information that indicates the presence
	# or the possibility of presence of an allergen prevails on information that indicates its absence

[github-throwaway]

From Slack:

It would be great to review some of the 2638 products that have a "no gluten" label + gluten identified as an allergen: https://world.openfoodfacts.org/label/no-gluten/allergen/gluten
to see if there are systematic issues that we could fix (e.g. wrong parsing of some ingredients)