Add revisioning of post meta, including ‘footnotes’ by default

src/wp-admin/includes/post.php

@@ -1961,15 +1961,73 @@ function wp_create_post_autosave( $post_data ) {
 		 * @param array $new_autosave Post array - the autosave that is about to be saved.
 		 */
 		do_action( 'wp_creating_autosave', $new_autosave );
-
+		wp_autosave_post_revisioned_meta_fields( $new_autosave );
 		return wp_update_post( $new_autosave );
 	}
 
 	// _wp_put_post_revision() expects unescaped.
 	$post_data = wp_unslash( $post_data );
 
 	// Otherwise create the new autosave as a special post revision.
-	return _wp_put_post_revision( $post_data, true );
+	$revision = _wp_put_post_revision( $post_data, true );
+
+	// Update the revisioned meta data as well.
+	wp_autosave_post_revisioned_meta_fields( $revision );
+	return $revision;
+}
+
+/**
+ * Autosave the revisioned meta fields.
+ *
+ * Iterates thru the revisioned meta fields and checks each to see if they are set,
+ * and have a changed value. If so, the meta value is saved and attached to the autosave.
+ *
+ * @since 6.4.0
+ *
+ * @param Post object $new_autosave The new post being autosaved.
+ */
+function wp_autosave_post_revisioned_meta_fields( $new_autosave ) {
+	/*
+	 * The post data arrives as either $_POST['data']['wp_autosave'] or the $_POST
+	 * itself. This sets $posted_data to the correct variable.
+	 *
+	 * Ignoring sanitization to avoid altering meta. Ignoring the nonce check because
+	 * this is hooked on inner core hooks where a valid nonce was already checked.
+	 *
+	 * @phpcs:disable WordPress.Security
+	 */
+	$posted_data = isset( $_POST['data']['wp_autosave'] ) ? $_POST['data']['wp_autosave'] : $_POST;
+	// phpcs:enable
+
+	/*
+	 * Go thru the revisioned meta keys and save them as part of the autosave, if
+	 * the meta key is part of the posted data, the meta value is not blank and
+	 * the the meta value has changes from the last autosaved value.
+	 */
+	foreach ( wp_post_revision_meta_keys() as $meta_key ) {
+
+		if (
+		isset( $posted_data[ $meta_key ] ) &&
+		get_post_meta( $new_autosave['ID'], $meta_key, true ) !== wp_unslash( $posted_data[ $meta_key ] )
+		) {
+			/*
+			 * Use the underlying delete_metadata() and add_metadata() functions
+			 * vs delete_post_meta() and add_post_meta() to make sure we're working
+			 * with the actual revision meta.
+			 */
+			delete_metadata( 'post', $new_autosave['ID'], $meta_key );
+
+			/*
+			 * One last check to ensure meta value not empty().
+			 */
+			if ( ! empty( $posted_data[ $meta_key ] ) ) {
+				/*
+				 * Add the revisions meta data to the autosave.
+				 */
+				add_metadata( 'post', $new_autosave['ID'], $meta_key, $posted_data[ $meta_key ] );
+			}
+		}
+	}
 }
 
 /**

src/wp-includes/default-filters.php

@@ -719,4 +719,10 @@
 // CPT wp_block custom postmeta field.
 add_action( 'init', 'wp_create_initial_post_meta' );
 
+// Including revisioned meta when considering whether a post revision has changed.
+add_filter( 'wp_save_post_revision_post_has_changed', 'wp_check_revisioned_meta_fields_have_changed', 10, 3 );
+
+// Save revisioned post meta immediately after a revision is saved
+add_action( '_wp_put_post_revision', 'wp_save_revisioned_meta_fields', 10, 2 );
+
 unset( $filter, $action );

src/wp-includes/meta.php

@@ -1367,6 +1367,7 @@ function sanitize_meta( $meta_key, $meta_value, $object_type, $object_subtype =
  * @since 4.9.8 The `$object_subtype` argument was added to the arguments array.
  * @since 5.3.0 Valid meta types expanded to include "array" and "object".
  * @since 5.5.0 The `$default` argument was added to the arguments array.
+ * @since 6.4.0 The `$revisions_enabled` argument was added to the arguments array.
  *
  * @param string       $object_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
  *                                  or any other object type with an associated meta table.
@@ -1392,6 +1393,7 @@ function sanitize_meta( $meta_key, $meta_value, $object_type, $object_subtype =
  *                                         support for custom fields for registered meta to be accessible via REST.
  *                                         When registering complex meta values this argument may optionally be an
  *                                         array with 'schema' or 'prepare_callback' keys instead of a boolean.
+ *     @type bool       $revisions_enabled Whether to enable revisions support for this meta_key.
  * }
  * @param string|array $deprecated Deprecated. Use `$args` instead.
  * @return bool True if the meta key was successfully registered in the global array, false if not.
@@ -1400,11 +1402,16 @@ function sanitize_meta( $meta_key, $meta_value, $object_type, $object_subtype =
  */
 function register_meta( $object_type, $meta_key, $args, $deprecated = null ) {
 	global $wp_meta_keys;
+	global $wp_revisioned_meta_keys;
 
 	if ( ! is_array( $wp_meta_keys ) ) {
 		$wp_meta_keys = array();
 	}
 
+	if ( ! is_array( $wp_revisioned_meta_keys ) ) {
+		$wp_revisioned_meta_keys = array();
+	}
+
 	$defaults = array(
 		'object_subtype'    => '',
 		'type'              => 'string',
@@ -1414,6 +1421,7 @@ function register_meta( $object_type, $meta_key, $args, $deprecated = null ) {
 		'sanitize_callback' => null,
 		'auth_callback'     => null,
 		'show_in_rest'      => false,
+		'revisions_enabled' => false,
 	);
 
 	// There used to be individual args for sanitize and auth callbacks.
@@ -1459,6 +1467,11 @@ function register_meta( $object_type, $meta_key, $args, $deprecated = null ) {
 		}
 	}
 
+	// Store the revisioned meta fields.
+	if ( isset( $args['revisions_enabled'] ) && $args['revisions_enabled'] && ! in_array( $meta_key, $wp_revisioned_meta_keys ) ) {
+		array_push( $wp_revisioned_meta_keys, $meta_key );
+	}
+
 	$object_subtype = ! empty( $args['object_subtype'] ) ? $args['object_subtype'] : '';
 
 	// If `auth_callback` is not provided, fall back to `is_protected_meta()`.

src/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

@@ -673,6 +673,9 @@ public function create_item( $request ) {
 			);
 		}
 
+		// Don't save the post meta revision because they aren't stored yet.
+		remove_action( '_wp_put_post_revision', 'wp_save_revisioned_meta_fields', 10, 2 );
+
 		$post_id = wp_insert_post( wp_slash( (array) $prepared_post ), true, false );
 
 		if ( is_wp_error( $post_id ) ) {
@@ -743,6 +746,13 @@ public function create_item( $request ) {
 			}
 		}
 
+		// Update any revisioned meta.
+		$revisions = wp_get_post_revisions( $post_id, array( 'posts_per_page' => 1 ) );
+		if ( ! empty( $revisions ) ) {
+			$revision  = array_shift( $revisions );
+			wp_save_revisioned_meta_fields( $revision->ID, $post_id );
+		}
+
 		$post          = get_post( $post_id );
 		$fields_update = $this->update_additional_fields_for_object( $post, $request );
 
@@ -876,6 +886,9 @@ public function update_item( $request ) {
 			);
 		}
 
+		// Don't save the post meta revision because they aren't stored yet.
+		remove_action( '_wp_put_post_revision', 'wp_save_revisioned_meta_fields', 10, 2 );
+
 		// Convert the post object to an array, otherwise wp_update_post() will expect non-escaped input.
 		$post_id = wp_update_post( wp_slash( (array) $post ), true, false );
 
@@ -928,6 +941,12 @@ public function update_item( $request ) {
 				return $meta_update;
 			}
 		}
+		// Update any revisioned meta.
+		$revisions = wp_get_post_revisions( $post_id, array( 'posts_per_page' => 1 ) );
+		if ( ! empty( $revisions ) ) {
+			$revision  = array_shift( $revisions );
+			wp_save_revisioned_meta_fields( $revision->ID, $post_id );
+		}
 
 		$post          = get_post( $post_id );
 		$fields_update = $this->update_additional_fields_for_object( $post, $request );

src/wp-includes/rest-api/endpoints/class-wp-rest-revisions-controller.php

@@ -24,6 +24,14 @@ class WP_REST_Revisions_Controller extends WP_REST_Controller {
 	 */
 	private $parent_post_type;
 
+	/**
+	 * Instance of a revision meta fields object.
+	 *
+	 * @since 4.7.0
+	 * @var WP_REST_Revision_Meta_Fields
+	 */
+	protected $meta;
+
 	/**
 	 * Parent controller.
 	 *
@@ -60,6 +68,7 @@ public function __construct( $parent_post_type ) {
 		$this->rest_base         = 'revisions';
 		$this->parent_base       = ! empty( $post_type_object->rest_base ) ? $post_type_object->rest_base : $post_type_object->name;
 		$this->namespace         = ! empty( $post_type_object->rest_namespace ) ? $post_type_object->rest_namespace : 'wp/v2';
+		$this->meta              = new WP_REST_Revision_Meta_Fields( 'revision' );
 	}
 
 	/**
@@ -619,6 +628,10 @@ public function prepare_item_for_response( $item, $request ) {
 			);
 		}
 
+		if ( rest_is_field_included( 'meta', $fields ) ) {
+			$data['meta'] = $this->meta->get_value( $post->ID, $request );
+		}
+
 		$context  = ! empty( $request['context'] ) ? $request['context'] : 'view';
 		$data     = $this->add_additional_fields_to_object( $data, $request );
 		$data     = $this->filter_response_by_context( $data, $context );
@@ -752,6 +765,8 @@ public function get_item_schema() {
 			$schema['properties']['guid'] = $parent_schema['properties']['guid'];
 		}
 
+		$schema['properties']['meta'] = $this->meta->get_field_schema();
+
 		$this->schema = $schema;
 
 		return $this->add_additional_fields_schema( $this->schema );

src/wp-includes/rest-api/fields/class-wp-rest-revision-meta-fields.php

@@ -0,0 +1,111 @@
+<?php
+/**
+ * REST API: WP_REST_Revision_Meta_Fields class
+ *
+ * @package WordPress
+ * @subpackage REST_API
+ * @since 6.4.0
+ */
+
+/**
+ * Core class used to manage meta values for revisions via the REST API.
+ *
+ * @since 6.4.0
+ *
+ * @see WP_REST_Meta_Fields
+ */
+class WP_REST_Revision_Meta_Fields extends WP_REST_Meta_Fields {
+
+	/**
+	 * Revision type to register fields for.
+	 *
+	 * @since 6.4.0
+	 * @var string
+	 */
+	protected $post_type;
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 6.4.0
+	 *
+	 * @param string $post_type Revision type to register fields for.
+	 */
+	public function __construct( $post_type ) {
+		$this->post_type = $post_type;
+	}
+
+	/**
+	 * Retrieves the post meta type.
+	 *
+	 * @since 6.4.0
+	 *
+	 * @return string The meta type.
+	 */
+	protected function get_meta_type() {
+		return 'revision';
+	}
+
+	/**
+	 * Retrieves the post meta subtype.
+	 *
+	 * @since 6.4.0
+	 *
+	 * @return string Subtype for the meta type, or empty string if no specific subtype.
+	 */
+	protected function get_meta_subtype() {
+		return $this->post_type;
+	}
+
+	/**
+	 * Retrieves the type for register_rest_field().
+	 *
+	 * @since 6.4.0
+	 *
+	 * @see register_rest_field()
+	 *
+	 * @return string The REST field type.
+	 */
+	public function get_rest_field_type() {
+		return $this->post_type;
+	}
+
+	/**
+	 * Retrieves the meta field value.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @param int             $object_id Object ID to fetch meta for.
+	 * @param WP_REST_Request $request   Full details about the request.
+	 * @return array Array containing the meta values keyed by name.
+	 */
+	public function get_value( $object_id, $request ) {
+		$data = get_post_meta( $object_id );
+		return $data;
+	}
+
+	/**
+	 * Retrieves raw metadata value for the specified object.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @param string $meta_type Type of object metadata is for. Accepts 'post', 'comment', 'term', 'user',
+	 *                          or any other object type with an associated meta table.
+	 * @param int    $object_id ID of the object metadata is for.
+	 * @param string $meta_key  Optional. Metadata key. If not specified, retrieve all metadata for
+	 *                          the specified object. Default empty string.
+	 * @param bool   $single    Optional. If true, return only the first value of the specified `$meta_key`.
+	 *                          This parameter has no effect if `$meta_key` is not specified. Default false.
+	 * @return mixed An array of values if `$single` is false.
+	 *               The value of the meta field if `$single` is true.
+	 *               False for an invalid `$object_id` (non-numeric, zero, or negative value),
+	 *               or if `$meta_type` is not specified.
+	 *               Null if the value does not exist.
+	 */
+	function get_metadata_raw( $meta_type, $object_id, $meta_key = '', $single = false ) {
+		$data = get_post_meta( $object_id, $request );
+		return $data;
+	}
+
+
+}