Add: Footnotes support in core.

[jorgefilipecosta]

Core version of WordPress/gutenberg#58573.

Adds footnote support for custom post types in the core. Creates a new footnotes support key.
By default, every post that meets footnotes requirements has support for footnotes.
Developers can now remove footnotes support with:

remove_post_type_support( 'my_type', 'footnotes' );

Testing

Added the following post type:

function cptui_register_my_cpts_testfootnotes() {

	/**
	 * Post Type: Test foot notes.
	 */

	$labels = [
		"name" => esc_html__( "Test foot notes", "twentytwentyfour" ),
		"singular_name" => esc_html__( "Test foot note", "twentytwentyfour" ),
	];

	$args = [
		"label" => esc_html__( "Test foot notes", "twentytwentyfour" ),
		"labels" => $labels,
		"description" => "",
		"public" => true,
		"publicly_queryable" => true,
		"show_ui" => true,
		"show_in_rest" => true,
		"rest_base" => "",
		"rest_controller_class" => "WP_REST_Posts_Controller",
		"rest_namespace" => "wp/v2",
		"has_archive" => false,
		"show_in_menu" => true,
		"show_in_nav_menus" => true,
		"delete_with_user" => false,
		"exclude_from_search" => false,
		"capability_type" => "post",
		"map_meta_cap" => true,
		"hierarchical" => false,
		"can_export" => false,
		"rewrite" => [ "slug" => "testfootnotes", "with_front" => true ],
		"query_var" => true,
		"supports" => [ "title", "editor", "thumbnail", "custom-fields", "revisions" ],
		"show_in_graphql" => false,
	];

	register_post_type( "testfootnotes", $args );
}

add_action( 'init', 'cptui_register_my_cpts_testfootnotes' );

I have confirmed that the footnotes are functioning correctly on the specified post type.

Furthermore, I have removed the "custom-fields" support from the post type and confirmed that the footnotes are no longer available on the post type.

In addition, I have verified that remove_post_type_support( 'page', 'footnotes' ); successfully removes footnotes support from pages.

[github-actions]

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[mukeshpanchal27]

In src/wp-includes/class-wp-post-type.php, we have already added support for a specific post type. Why are we checking a similar condition here again?

[jorgefilipecosta]

The reason for the check was that meanwhile, a plugin may have removed a support after the code in src/wp-includes/class-wp-post-type.php executed.

[mukeshpanchal27]

For multiple conditions i personally follow.

Suggested change

	if ( post_type_supports( $this->name, 'editor' ) && post_type_supports( $this->name, 'custom-fields' ) && post_type_supports( $this->name, 'revisions' ) && ! post_type_supports( $this->name, 'footnotes' ) ) {
	if (
	post_type_supports( $this->name, 'editor' ) &&
	post_type_supports( $this->name, 'custom-fields' ) &&
	post_type_supports( $this->name, 'revisions' ) &&
	! post_type_supports( $this->name, 'footnotes' )
	) {

[jorgefilipecosta]

Thank you for the suggestion 👍 I'm applying it at WordPress/gutenberg#58882.

[peterwilsoncc]

Cross posting my change request from the Gutenberg PR WordPress/gutenberg#58573 (review) that I think it's best to make the footnotes opt in for CPTs.

Let's finalise the approach in the upstream repo rather than discussing in two PRs.

[github-actions]

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Core SVN

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Props: jorgefilipecosta, mukesh27, peterwilsoncc.

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Co-authored-by: jorgefilipecosta <jorgefilipecosta@git.wordpress.org>
Co-authored-by: mukeshpanchal27 <mukesh27@git.wordpress.org>
Co-authored-by: peterwilsoncc <peterwilsoncc@git.wordpress.org>

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[jorgefilipecosta]

Closing this PR following @ellatrix suggestion at WordPress/gutenberg#58573 (comment).