Fix Interactivity API setup

src/Interactivity/woo-directives.php

@@ -1,6 +1,4 @@
 <?php
-require_once __DIR__ . '/directives/wp-html.php';
-
 require_once __DIR__ . '/directives/class-woo-directive-context.php';
 require_once __DIR__ . '/directives/class-woo-directive-store.php';
 require_once __DIR__ . '/directives/woo-process-directives.php';

woocommerce-gutenberg-products-block.php

@@ -287,6 +287,33 @@ function woocommerce_blocks_plugin_outdated_notice() {
 
 add_action( 'admin_notices', 'woocommerce_blocks_plugin_outdated_notice' );
 
-// Include the Interactivity API.
-require_once __DIR__ . '/src/Interactivity/woo-directives.php';
+/**
+ * Disable the Interactivity API if the required `WP_HTML_Tag_Processor` class
+ * doesn't exist, regardless of whether it was enabled manually.
+ *
+ * @param bool $enabled Current filter value.
+ * @return bool True if _also_ the `WP_HTML_Tag_Processor` class was found.
+ */
+function woocommerce_blocks_has_wp_html_tag_processor( $enabled ) {
+	return $enabled && class_exists( 'WP_HTML_Tag_Processor' );
+}
+add_filter(
+	'woocommerce_blocks_enable_interactivity_api',
+	'woocommerce_blocks_has_wp_html_tag_processor',
+	999
+);
 
+/**
+ * Load and setup the Interactivity API if enabled.
+ */
+function woocommerce_blocks_interactivity_setup() {
+	$is_enabled = apply_filters(
+		'woocommerce_blocks_enable_interactivity_api',
+		false
+	);
+
+	if ( $is_enabled ) {
+		require_once __DIR__ . '/src/Interactivity/woo-directives.php';
+	}
+}
+add_action( 'plugins_loaded', 'woocommerce_blocks_interactivity_setup' );