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

src/wp-admin/includes/post.php

@@ -1957,19 +1957,84 @@ function wp_create_post_autosave( $post_data ) {
 		 * Fires before an autosave is stored.
 		 *
 		 * @since 4.1.0
+		 * @since 6.4.0 The `$is_update` parameter was added to indicate if the autosave is being updated or was newly created.
 		 *
 		 * @param array $new_autosave Post array - the autosave that is about to be saved.
+		 * @param bool  $is_update    Whether this is an existing autosave.
 		 */
-		do_action( 'wp_creating_autosave', $new_autosave );
-
+		do_action( 'wp_creating_autosave', $new_autosave, true );
 		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 );
+
+	if ( ! is_wp_error( $revision ) ) {
+
+		/** This action is documented in wp-admin/includes/post.php */
+		do_action( 'wp_creating_autosave', get_post( $revision, ARRAY_A ), false );
+	}
+
+	return $revision;
+}
+
+/**
+ * Autosave the revisioned meta fields.
+ *
+ * Iterates through 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 array $new_autosave The new post data 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
+
+	$post_type = get_post_type( $new_autosave['post_parent'] );
+
+	/*
+	 * 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( $post_type ) 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

@@ -409,6 +409,7 @@
 add_action( 'plugins_loaded', 'wp_maybe_load_embeds', 0 );
 add_action( 'shutdown', 'wp_ob_end_flush_all', 1 );
 // Create a revision whenever a post is updated.
+add_action( 'wp_after_insert_post', 'wp_save_post_revision_on_insert', 9, 3 );
 add_action( 'post_updated', 'wp_save_post_revision', 10, 1 );
 add_action( 'publish_post', '_publish_post_hook', 5, 1 );
 add_action( 'transition_post_status', '_transition_post_status', 5, 3 );
@@ -716,6 +717,18 @@
 // CPT wp_block custom postmeta field.
 add_action( 'init', 'wp_create_initial_post_meta' );
 
+// Include 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 );
+
+// Include revisioned meta when creating or updating an autosave revision.
+add_action( 'wp_creating_autosave', 'wp_autosave_post_revisioned_meta_fields' );
+
+// When restoring revisions, also restore revisioned meta.
+add_action( 'wp_restore_post_revision', 'wp_restore_post_revision_meta', 10, 2 );
+
 // Font management.
 add_action( 'wp_head', 'wp_print_font_faces', 50 );
 

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 +1393,8 @@ 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. Can only be used when the
+ *                                         object type is 'post'.
  * }
  * @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.
@@ -1414,6 +1417,7 @@ 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 +1463,13 @@ function register_meta( $object_type, $meta_key, $args, $deprecated = null ) {
 		}
 	}
 
+	// If the object_type is set, require a type that supports revisions when setting revisions_enabled to true.
+	if ( ! empty( $object_type ) && $args['revisions_enabled'] && ! post_type_supports( $object_type, 'revisions' ) ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Meta keys cannot enable revisions support unless the object type supports revisions.' ), '6.4.0' );
+
+		return false;
+	}
+
 	$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-autosaves-controller.php

@@ -234,8 +234,8 @@
 			 */
 			$autosave_id = wp_update_post( wp_slash( (array) $prepared_post ), true );
 		} else {
-			// Non-draft posts: create or update the post autosave.
-			$autosave_id = $this->create_post_autosave( (array) $prepared_post );
+			// Non-draft posts: create or update the post autosave. Pass the meta data.
+			$autosave_id = $this->create_post_autosave( (array) $prepared_post, $request->get_param( 'meta' ) );
 		}
 
 		if ( is_wp_error( $autosave_id ) ) {
@@ -348,11 +348,13 @@
 	 * From wp-admin/post.php.
 	 *
 	 * @since 5.0.0
+	 * @since 6.4.0 The `$meta` parameter was added.
 	 *
 	 * @param array $post_data Associative array containing the post data.
+	 * @param array $meta      Associative array containing the post meta data.
 	 * @return mixed The autosave revision ID or WP_Error.
 	 */
-	public function create_post_autosave( $post_data ) {
+	public function create_post_autosave( $post_data, array $meta = array() ) {
 
 		$post_id = (int) $post_data['ID'];
 		$post    = get_post( $post_id );
@@ -372,6 +374,21 @@
 			}
 		}
 
+		// Check if meta values have changed.
+		if ( ! empty( $meta ) ) {
+			$revisioned_meta_keys = wp_post_revision_meta_keys( $post->post_type );
+			foreach ( $revisioned_meta_keys as $meta_key ) {
+				// get_metadata_raw is used to avoid retrieving the default value.
+				$old_meta = get_metadata_raw( 'post', $post_id, $meta_key, true );
+				$new_meta = isset( $meta[ $meta_key ] ) ? $meta[ $meta_key ] : '';
+
+				if ( $new_meta !== $old_meta ) {
+					$autosave_is_different = true;
+					break;
+				}
+			}
+		}
+
 		$user_id = get_current_user_id();
 
 		// Store one autosave per author. If there is already an autosave, overwrite it.
@@ -390,11 +407,26 @@
 			do_action( 'wp_creating_autosave', $new_autosave );
 
 			// wp_update_post() expects escaped array.
-			return wp_update_post( wp_slash( $new_autosave ) );
+			$revision_id = wp_update_post( wp_slash( $new_autosave ) );
+		} else {
+			// Create the new autosave as a special post revision.
+			$revision_id = _wp_put_post_revision( $post_data, true );
+		}
+
+		if( is_wp_error( $revision_id ) ) {
+			return $revision_id;
+		}
+
+		// Attached any passed meta values that have revisions enabled.
+		if ( ! empty( $meta ) && $revision_id ) {
+			foreach ( $revisioned_meta_keys as $meta_key ) {
+				if ( isset( $meta[ $meta_key ] ) ) {
+					update_metadata( 'post', $revision_id, $meta_key, $meta[ $meta_key ] );
+				}
+			}
 		}
 
-		// Create the new autosave as a special post revision.
-		return _wp_put_post_revision( $post_data, true );
+		return $revision_id;
 	}
 
 	/**

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 6.4.0
+	 * @var WP_REST_Post_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_Post_Meta_Fields( $parent_post_type );
 	}
 
 	/**
@@ -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 );