register_taxonomy_for_object_type() sets duplicate values

[kevinB]

If register_taxonomy_for_object_type() is called for an object type which is already present in the taxonomy's object_type array, a duplicate value is added to the array.

This is a common occurrence with user-modifiable taxonomy/type definition in plugins such as GD Custom Posts and Taxonomies, when:

• register_taxonomy() is called with object_type argument, based on a taxonomy configuration.

• register_taxonomy_for_object_type() is subsequently called, based on a post type configuration.

[scribu]

Do duplicates there actually have any adverse effects?

[kevinB]

It can cause redundant processing or duplicate/erroneous UI generation in taxonomy-related plugins.

You're right to flag it as minor, but it's also a minor fix. My thinking is if $tx->object_type is supported API, are duplicate object_type values ever appropriate and if not, why leave validation to the client?

[scribu]

Makes sense. Patch is dead simple.

[dd32]

(In [17688]) Prevent $taxonony->object_type containing duplicate values. Initial patch props kevinB. Fixes #16951