Introduce `is_term_publicly_viewable()` function

[johnbillion]

In #49380 the is_post_publicly_viewable() function was introduced which encapsulates the logic used to determine if a post type is visible to anonymous users.

We should do the same for terms via an is_term_publicly_viewable() function. Although the logic for terms is more straight forward this serves the same purpose as introducing the corresponding function for posts -- to centralise and reduce the logic needed to validate a term and determine if it's publicly viewable.

There are several places in core that would benefit from an additional "viewable" check before outputting a link to a term, but those changes can happen in a follow-up ticket.

Trac ticket: https://core.trac.wordpress.org/ticket/56215

[johnbillion]

Before:

$term = get_term( $term_id );

if ( ( $term instanceof WP_Term ) && is_taxonomy_viewable( $term->taxonomy ) ) {
    $link = get_term_link( $term_id );
}

After:

if ( is_term_publicly_viewable( $term_id ) ) {
    $link = get_term_link( $term_id );
}

[johnbillion]

In 53893:

Taxonomy: Introduce the is_term_publicly_viewable() function.

This is the taxonomy term counterpart to the is_post_publicly_viewable() function. Although the logic for terms is more straight forward this serves the same purpose as introducing the corresponding function for posts -- to centralise and reduce the logic needed to validate a term and determine if it's publicly viewable.

Props peterwilsoncc, costdev, johnbillion

Fixes #56215

https://core.trac.wordpress.org/changeset/53893

https://core.trac.wordpress.org/changeset/53893

[johnbillion]

In 53894:

Taxonomy: Add a test file that was missed in [53893].

See #56215

[peterwilsoncc]

@johnbillion Something that had slipped my mind until recently was the potential for unsplit terms.

This was prompted by #56351 in which a recent change introduced a bug for unsplit terms so we should probably consider them for this new function too. Or deal with unsplit terms in some other way but I don't know what that is -- a topic for the other ticket.

[johnbillion]

There are a few places in core now that don't handle shared terms, ie by only passing a term ID to get_term().

Examples:

• ​https://github.com/WordPress/wordpress-develop/blob/d51b039755431df833162d1a3a72ac5d3812ee24/src/wp-includes/rest-api/search/class-wp-rest-term-search-handler.php#L142-L147
• ​https://github.com/WordPress/wordpress-develop/blob/d51b039755431df833162d1a3a72ac5d3812ee24/src/wp-includes/rest-api.php#L3138-L3146

Do you think this function needs a $taxonomy parameter?

[peterwilsoncc]

Replying to johnbillion:

Do you think this function needs a $taxonomy parameter?

TBA... I am not sure what I think is best at the moment.

I'm continuing to consider this and will let you know once I cement my thoughts. I'll reopen the ticket if I think it ought to be added.