Clean up duplicate post types in featured content

[BinaryMoon]

Add array_unique for the post_types list.

array_merge appends arrays, and since post is set as the default, it means that for many post will be listed twice.

For example in Canard (an Automattic theme) where post_type is set to post and page the post_type will become array( 'post', 'post', 'page' )
https://github.com/Automattic/themes/blob/b8444897830573b47505a19623e1f3459a45aac4/canard/inc/jetpack.php#L22

By filtering the list we prevent the register_taxonomy_for_object_type from being called multiple times for the same post type, and we ensure the post_types are listed once when we later call get_posts.

To be honest I don't imagine it will make a huge amount of difference to anything but I was debugging a featured content issue in my theme and saw this and it confused me. This eliminates that confusion.

Testing instructions

To test you should add theme support for Jetpack Featured Content as normal, but make sure to include the additional post types.

add_theme_support( 'featured-content', array(
		'filter'      => 'canard_get_featured_posts',
		'description' => __( 'The featured content section displays on the front page above the header.', 'canard' ),
		'max_posts'   => 5,
		'post_types'  => array( 'post', 'page' ),
	) );

Then, somewhere in your theme, add:

var_dump( Featured_Content::$post_types );

And you should see that post is being listed twice.

[jetpackbot]

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[jeherve]

Could you add testing instructions to your PR so we can easily reproduce the issue and see if your branch fixes things?

Thank you!

[BinaryMoon]

done

[jeherve]

Thanks for the extra steps. It works well for me! 👍

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Please review this diff before merging: D18813-code. (newly created revision)