Don't show "Preview" for locked, non-public post types

[batmoo]

If a post_type is not public but has show_ui => true, we shouldn't show the preview link on the "This content is currently locked" notice.

[johnbillion]

The 'Go back' button needs fixing too. There may not be a referer if you've gone directly to the editing screen or opened it in a new tab, and the referer may be the same as the current page in the case where you've previously made a save and someone has just taken over.

[SergeyBiryukov]

Related: #17609 (#18956, #20029).

[aaroncampbell]

It looks like we show a preview link in the update notice in this same situation (public=>false, show_ui=>true), but it 404s.

[aaroncampbell]

Regarding my previous comment, it looks like you can use the post_updated_messages filter to add your own custom updated messages for your post types. I think this is sufficient for someone to remove the preview link if they want. If we wanted to handle this automatically we could, but it didn't seem as necessary there.

It also looks like this should be based on publicly_queryable not public. 24139.diff​ does just that. It hides the preview button by default if the post type is not publicly_queryable. I also leaves in the preview_post_link filter even for those post types, so you could override this if you wanted by using that filter to return a preview URL.

[markjaquith]

24139.diff​ works for me with a non-public CPT I tested.

[nacin]

publicly_queryable is an odd one. pages have it set to false, ostensibly because you can't do ?post_type=page and expect to get back a list of pages. public is much safer.

[markjaquith]

Confirmed that public is how we do it for the Publish meta box.

[nacin]

In 24799:

Don't show "Preview" for locked, non-public post types. props aaroncampbell. fixed #24139.