Introduce `is_post_status_viewable()` and `is_post_viewable()` functions.

[peterwilsoncc]

WordPress currently has the function is_post_type_viewable() to determine if a post type is visible to anonymous users via the publicly_queryable setting when registering the post type.

To enable easily determining when a post should be publicly viewable, I propose the following functions be introduced.

is_post_status_viewable( array|string $post_status ) : bool

Determines if post status is publicly viewable based on public/protected/publicly_queryable settings when registered.

is_post_viewable( int|WP_Post $post = null ) : bool

Determines if a post is viewable based on the outcome of is_post_type_viewable() and is_post_status_viewable().

Defaults to current post in loop, ie result of get_post().

https://core.trac.wordpress.org/ticket/49380

Words.

[whyisjake]

I like the direction here!

[SergeyBiryukov]

The PR looks good to me.

[peterwilsoncc]

Need to review this further, as "viewable" actually refers to publicly queryable, as opposed to public, I just need to double check is_post_viewable() makes sense.

I think is_*_public() functions would also make sense but that can be another ticket for another day.

[peterwilsoncc]

Reviewing WP::parse_query, it doesn't look like the post status object's publicly_queryable property is used anywhere.

Removing from milestone and the commit keyword as a result. I'll close it once I've got clarification.

[peterwilsoncc]

@SergeyBiryukov @whyisjake

Closing this off as post_status is not publicly queryable (it's in WP::$private_query_vars rather than $public_query_vars).

This can probably be dealt with if Post Statuses move beyond the simple standard class.

[peterwilsoncc]

I realised this was necessary while working on #5272, reopening.

https://core.trac.wordpress.org/ticket/49380

Separates this out from PR #863.

[peterwilsoncc]

In 50130:

Posts, Post Types: Additional functions to check if a post is publicly viewable.

Introduces is_post_status_viewable() as a sibling to is_post_type_viewable(). Internal and protected statuses are never considered viewable. For built in posts statuses the public attribute is checked, for custom statuses the publicly_queryable attribute is checked.

Introduces is_post_publicly_viewable() for determining if an individual post can be viewed by logged out users. A post is considered viewable if both is_post_status_viewable() and is_post_type_viewable() return true for the post's attributes.

Additionally modifies is_post_type_viewable() to return false if an unregistered post type is passed to the function to avoid attempting to access properties on a non-object.

Props peterwilsoncc, SergeyBiryukov, whyisjake, TimothyBlynJacobs.
Fixes #49380.

[hellofromTonya]

Needs dev note for the new functions.

[audrasjb]

Dev note published: ​https://make.wordpress.org/core/2021/02/18/introducing-additional-functions-to-check-if-a-post-is-publicly-viewable-in-wordpress-5-7/

[Cybr]

Since taxonomies behave much like posts and have a similarly named function, is_taxonomy_viewable(), will those receive changes akin to this ticket, or has this ticket/patch left an accidental discrepancy?

Edit: I reckon it a bit too late that terms don't have statuses. Ignore me :)