Footnotes: use core’s meta revisioning if available (#52988)

# Conflicts:
#	packages/block-library/src/footnotes/index.php

lib/compat/plugin/footnotes.php

@@ -0,0 +1,250 @@
+<?php
+/**
+ * Compatibility shim for the footnotes bloct to enable test passing while awaiting the tested code to be merged to core.
+ *
+ * See https://github.com/WordPress/gutenberg/pull/52988.
+ *
+ * Once merged, this shim can be removed.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Remove footnote revision hooks when plugin is running on a version of core that already supports meta revisions.
+ */
+if ( function_exists( 'wp_post_revision_meta_keys' ) ) {
+	if ( has_action( 'rest_after_insert_post', 'wp_add_footnotes_revisions_to_post_meta' ) ) {
+		remove_action( 'rest_after_insert_post', 'wp_add_footnotes_revisions_to_post_meta' );
+	}
+	if ( has_action( 'rest_after_insert_page', 'wp_add_footnotes_revisions_to_post_meta' ) ) {
+		remove_action( 'rest_after_insert_page', 'wp_add_footnotes_revisions_to_post_meta' );
+	}
+	if ( has_action( 'wp_after_insert_post', 'wp_save_footnotes_meta' ) ) {
+		remove_action( 'wp_after_insert_post', 'wp_save_footnotes_meta' );
+	}
+	if ( has_action( '_wp_put_post_revision', 'wp_keep_footnotes_revision_id' ) ) {
+		remove_action( '_wp_put_post_revision', 'wp_keep_footnotes_revision_id' );
+	}
+	if ( has_action( 'wp_restore_post_revision', 'wp_restore_footnotes_from_revision' ) ) {
+		remove_action( 'wp_restore_post_revision', 'wp_restore_footnotes_from_revision' );
+	}
+	if ( has_action( 'wp_creating_autosave', '_wp_rest_api_autosave_meta' ) ) {
+		remove_action( 'wp_creating_autosave', '_wp_rest_api_autosave_meta' );
+	}
+	if ( has_action( '_wp_put_post_revision', '_wp_rest_api_autosave_meta' ) ) {
+		remove_action( '_wp_put_post_revision', '_wp_rest_api_autosave_meta' );
+	}
+	if ( has_filter( 'rest_pre_insert_post', '_wp_rest_api_force_autosave_difference' ) ) {
+		remove_filter( 'rest_pre_insert_post', '_wp_rest_api_force_autosave_difference' );
+	}
+} else {
+	/**
+	 * For versions of core that don't support meta revisions, use hooks to add.
+	 */
+	if ( ! function_exists( 'wp_save_footnotes_meta' ) ) {
+		/**
+		 * Saves the footnotes meta value to the revision.
+		 *
+		 * @since 6.3.0
+		 * @since 6.4.0 Core added post meta revisions, so this is no longer needed.
+		 *
+		 * @param int $revision_id The revision ID.
+		 */
+		function wp_save_footnotes_meta( $revision_id ) {
+			$post_id = wp_is_post_revision( $revision_id );
+
+			if ( $post_id ) {
+				$footnotes = get_post_meta( $post_id, 'footnotes', true );
+
+				if ( $footnotes ) {
+					// Can't use update_post_meta() because it doesn't allow revisions.
+					update_metadata( 'post', $revision_id, 'footnotes', wp_slash( $footnotes ) );
+				}
+			}
+		}
+		if ( ! function_exists( 'wp_post_revision_meta_keys' ) ) {
+			add_action( 'wp_after_insert_post', 'wp_save_footnotes_meta' );
+		}
+	}
+
+	if ( ! function_exists( 'wp_keep_footnotes_revision_id' ) ) {
+		/**
+		 * Keeps track of the revision ID for "rest_after_insert_{$post_type}".
+		 *
+		 * @since 6.3.0
+		 * @since 6.4.0 Core added post meta revisions, so this is no longer needed.
+		 *
+		 * @global int $wp_temporary_footnote_revision_id The footnote revision ID.
+		 *
+		 * @param int $revision_id The revision ID.
+		 */
+		function wp_keep_footnotes_revision_id( $revision_id ) {
+			global $wp_temporary_footnote_revision_id;
+			$wp_temporary_footnote_revision_id = $revision_id;
+		}
+		if ( ! function_exists( 'wp_post_revision_meta_keys' ) ) {
+			add_action( '_wp_put_post_revision', 'wp_keep_footnotes_revision_id' );
+		}
+	}
+
+	if ( ! function_exists( 'wp_add_footnotes_revisions_to_post_meta' ) ) {
+
+		/**
+		 * This is a specific fix for the REST API. The REST API doesn't update
+		 * the post and post meta in one go (through `meta_input`). While it
+		 * does fix the `wp_after_insert_post` hook to be called correctly after
+		 * updating meta, it does NOT fix hooks such as post_updated and
+		 * save_post, which are normally also fired after post meta is updated
+		 * in `wp_insert_post()`. Unfortunately, `wp_save_post_revision` is
+		 * added to the `post_updated` action, which means the meta is not
+		 * available at the time, so we have to add it afterwards through the
+		 * `"rest_after_insert_{$post_type}"` action.
+		 *
+		 * @since 6.3.0
+		 * @since 6.4.0 Core added post meta revisions, so this is no longer needed.
+		 *
+		 * @global int $wp_temporary_footnote_revision_id The footnote revision ID.
+		 *
+		 * @param WP_Post $post The post object.
+		 */
+		function wp_add_footnotes_revisions_to_post_meta( $post ) {
+			global $wp_temporary_footnote_revision_id;
+
+			if ( $wp_temporary_footnote_revision_id ) {
+				$revision = get_post( $wp_temporary_footnote_revision_id );
+
+				if ( ! $revision ) {
+					return;
+				}
+
+				$post_id = $revision->post_parent;
+
+				// Just making sure we're updating the right revision.
+				if ( $post->ID === $post_id ) {
+					$footnotes = get_post_meta( $post_id, 'footnotes', true );
+
+					if ( $footnotes ) {
+						// Can't use update_post_meta() because it doesn't allow revisions.
+						update_metadata( 'post', $wp_temporary_footnote_revision_id, 'footnotes', wp_slash( $footnotes ) );
+					}
+				}
+			}
+		}
+
+		if ( ! function_exists( 'wp_post_revision_meta_keys' ) ) {
+			add_action( 'rest_after_insert_post', 'wp_add_footnotes_revisions_to_post_meta' );
+			add_action( 'rest_after_insert_page', 'wp_add_footnotes_revisions_to_post_meta' );
+		}
+	}
+
+	if ( ! function_exists( 'wp_restore_footnotes_from_revision' ) ) {
+
+		/**
+		 * Restores the footnotes meta value from the revision.
+		 *
+		 * @since 6.3.0
+		 * @since 6.4.0 Core added post meta revisions, so this is no longer needed.
+		 *
+		 * @param int $post_id     The post ID.
+		 * @param int $revision_id The revision ID.
+		 */
+		function wp_restore_footnotes_from_revision( $post_id, $revision_id ) {
+			$footnotes = get_post_meta( $revision_id, 'footnotes', true );
+
+			if ( $footnotes ) {
+				update_post_meta( $post_id, 'footnotes', wp_slash( $footnotes ) );
+			} else {
+				delete_post_meta( $post_id, 'footnotes' );
+			}
+		}
+		if ( ! function_exists( 'wp_post_revision_meta_keys' ) ) {
+			add_action( 'wp_restore_post_revision', 'wp_restore_footnotes_from_revision', 10, 2 );
+		}
+	}
+
+	if ( ! function_exists( '_wp_rest_api_autosave_meta' ) ) {
+
+		/**
+		 * The REST API autosave endpoint doesn't save meta, so we can use the
+		 * `wp_creating_autosave` when it updates an exiting autosave, and
+		 * `_wp_put_post_revision` when it creates a new autosave.
+		 *
+		 * @since 6.3.0
+		 * @since 6.4.0 Core added post meta revisions, so this is no longer needed.
+		 *
+		 * @param int|array $autosave The autosave ID or array.
+		 */
+		function _wp_rest_api_autosave_meta( $autosave ) {
+			// Ensure it's a REST API request.
+			if ( ! defined( 'REST_REQUEST' ) || ! REST_REQUEST ) {
+				return;
+			}
+
+			$body = rest_get_server()->get_raw_data();
+			$body = json_decode( $body, true );
+
+			if ( ! isset( $body['meta']['footnotes'] ) ) {
+				return;
+			}
+
+			// `wp_creating_autosave` passes the array,
+			// `_wp_put_post_revision` passes the ID.
+			$id = is_int( $autosave ) ? $autosave : $autosave['ID'];
+
+			if ( ! $id ) {
+				return;
+			}
+
+			// Can't use update_post_meta() because it doesn't allow revisions.
+			update_metadata( 'post', $id, 'footnotes', wp_slash( $body['meta']['footnotes'] ) );
+		}
+
+		if ( ! function_exists( 'wp_post_revision_meta_keys' ) ) {
+			// See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L391C1-L391C1.
+			add_action( 'wp_creating_autosave', '_wp_rest_api_autosave_meta' );
+			// See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L398.
+			// Then https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/revision.php#L367.
+			add_action( '_wp_put_post_revision', '_wp_rest_api_autosave_meta' );
+		}
+	}
+
+	if ( ! function_exists( '_wp_rest_api_force_autosave_difference' ) ) {
+
+		/**
+		 * This is a workaround for the autosave endpoint returning early if the
+		 * revision field are equal. The problem is that "footnotes" is not real
+		 * revision post field, so there's nothing to compare against.
+		 *
+		 * This trick sets the "footnotes" field (value doesn't matter), which will
+		 * cause the autosave endpoint to always update the latest revision. That should
+		 * be fine, it should be ok to update the revision even if nothing changed. Of
+		 * course, this is temporary fix.
+		 *
+		 * @since 6.3.0
+		 * @since 6.4.0 Core added post meta revisions, so this is no longer needed.
+		 *
+		 * @param WP_Post         $prepared_post The prepared post object.
+		 * @param WP_REST_Request $request       The request object.
+		 *
+		 * See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L365-L384.
+		 * See https://github.com/WordPress/wordpress-develop/blob/2103cb9966e57d452c94218bbc3171579b536a40/src/wp-includes/rest-api/endpoints/class-wp-rest-autosaves-controller.php#L219.
+		 */
+		function _wp_rest_api_force_autosave_difference( $prepared_post, $request ) {
+			// We only want to be altering POST requests.
+			if ( $request->get_method() !== 'POST' ) {
+				return $prepared_post;
+			}
+
+			// Only alter requests for the '/autosaves' route.
+			if ( substr( $request->get_route(), -strlen( '/autosaves' ) ) !== '/autosaves' ) {
+				return $prepared_post;
+			}
+
+			$prepared_post->footnotes = '[]';
+			return $prepared_post;
+		}
+		if ( ! function_exists( 'wp_post_revision_meta_keys' ) ) {
+			add_filter( 'rest_pre_insert_post', '_wp_rest_api_force_autosave_difference', 10, 2 );
+		}
+	}
+}

lib/load.php

@@ -72,6 +72,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 
 // Gutenberg plugin compat.
 require __DIR__ . '/compat/plugin/edit-site-routes-backwards-compat.php';
+require __DIR__ . '/compat/plugin/footnotes.php';
 
 if ( ! class_exists( 'WP_HTML_Processor' ) ) {
 	require __DIR__ . '/compat/wordpress-6.4/html-api/class-wp-html-active-formatting-elements.php';