Add back-compat function for older Gutenberg and WP versions

apps/editing-toolkit/editing-toolkit-plugin/block-patterns/test/class-block-patterns-from-api-test.php

@@ -180,7 +180,7 @@ public function multiple_route_pattern_registration( $patterns_from_api_mock, $t
 			$request_mock = $this->createMock( \WP_REST_Request::class );
 			$request_mock->method( 'get_route' )->willReturn( $route );
 
-			load_block_patterns_from_api(
+			register_patterns_on_api_request(
 				function () use ( $patterns_from_api_mock ) {
 					$patterns_from_api_mock->register_patterns();
 				}

apps/editing-toolkit/editing-toolkit-plugin/full-site-editing-plugin.php

@@ -240,7 +240,7 @@ function load_wpcom_block_editor_nux() {
  * @param Function $register_patterns_func A function that when called will
  * register the relevant block patterns in the registry.
  */
-function load_block_patterns_from_api( $register_patterns_func ) {
+function register_patterns_on_api_request( $register_patterns_func ) {
 	/**
 	 * Load editing toolkit block patterns from the API.
 	 *
@@ -267,7 +267,7 @@ function load_block_patterns_from_api( $register_patterns_func ) {
 }
 add_filter(
 	'rest_dispatch_request',
-	load_block_patterns_from_api(
+	register_patterns_on_api_request(
 		function () {
 			( new Block_Patterns_From_API() )->register_patterns();
 		}
@@ -276,6 +276,34 @@ function () {
 	2
 );
 
+/**
+ * This function exists for back-compatibility. Patterns in Gutenberg v13.0.0 and
+ * newer are loaded over the API instead of injected into the document. While we
+ * register patterns in the API above, we still need to maintain compatibility
+ * with older Gutenberg versions and WP 5.9 without Gutenberg.
+ *
+ * This can be removed once the rest API approach is in core WordPress and available
+ * on Atomic and Simple sites. (Note that Atomic sites may disable the Gutenberg
+ * plugin, so we cannot guarantee its availability.)
+ *
+ * @param object $current_screen An object describing the wp-admin screen properties.
+ */
+function register_patterns_on_screen_load( $current_screen ) {
+	// No need to use this when the REST API approach is available.
+	if ( class_exists( 'WP_REST_Block_Pattern_Categories_Controller' ) ) {
+		return;
+	}
+
+	// is_block_editor should include site editor support.
+	if ( ! apply_filters( 'a8c_enable_block_patterns_api', false ) || ! $current_screen->is_block_editor ) {
+		return;
+	}
+
+	require_once __DIR__ . '/block-patterns/class-block-patterns-from-api.php';
+	( new Block_Patterns_From_API() )->register_patterns();
+}
+add_action( 'current_screen', __NAMESPACE__ . '\register_patterns_on_screen_load' );
+
 /**
  * Load Block Inserter Modifications module.
  */