Query loop / Post template: Enable post format filter

lib/compat/wordpress-6.7/taxonomy.php

@@ -0,0 +1,22 @@
+<?php
+/**
+ * Temporary compatibility code for post formats.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Add support for the post format taxonomy in the REST API.
+ * See wp-includes/taxonomy.php line 170.
+ *
+ * Needed to add post formats to the taxonomy filter in the query loop.
+ *
+ * @since 6.7.0
+ */
+add_filter(
+	'register_post_format_taxonomy_args',
+	function ( $args ) {
+		$args['show_in_rest'] = true;
+		return $args;
+	}
+);

lib/load.php

@@ -105,6 +105,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 // WordPress 6.7 compat.
 require __DIR__ . '/compat/wordpress-6.7/blocks.php';
 require __DIR__ . '/compat/wordpress-6.7/block-bindings.php';
+require __DIR__ . '/compat/wordpress-6.7/taxonomy.php';
 
 // Experimental features.
 require __DIR__ . '/experimental/block-editor-settings-mobile.php';

packages/block-library/src/post-template/edit.js

@@ -138,7 +138,19 @@ export default function PostTemplateEdit( {
 							( { slug } ) => slug === taxonomySlug
 						);
 						if ( taxonomy?.rest_base ) {
-							accumulator[ taxonomy?.rest_base ] = terms;
+							// Convert post format term ID's to a comma separated string,
+							// otherwise the Rest API will return a "rest_invalid_param" error
+							// and there will be a PHP fatal error from _post_format_request.
+							if (
+								taxonomy.rest_base === 'post_format' &&
+								Array.isArray( terms ) &&
+								terms.length > 0
+							) {
+								accumulator[ taxonomy.rest_base ] =
+									terms.join( ',' );
+							} else {
+								accumulator[ taxonomy.rest_base ] = terms;
+							}
 						}
 						return accumulator;
 					},