Update is_fse_active to account for a8c_disable_full_site_editing fil…

…ter (#13392)

* Update is_fse_active to account for a8c_disable_full_site_editing filter

* Fix method check and add dockblock comment

* Fix typo

* Update docblock to allow parser to create Codex page for filter


Co-authored-by: Glen Davies <glen.davies@a8c.com>
Co-authored-by: Jeremy Herve <jeremy@jeremy.hu>

sal/class.json-api-site-jetpack.php

@@ -187,13 +187,39 @@ function current_user_can( $role ) {
 		return current_user_can( $role );
 	}
 
+	/**
+	 * Check if full site editing should be considered as currently active. Full site editing
+	 * requires the FSE plugin to be installed and activated, as well the current
+	 * theme to be FSE compatible. The plugin can also be explicitly disabled via the
+	 * a8c_disable_full_site_editing filter.
+	 *
+	 * @since 7.7.0
+	 *
+	 * @return bool true if full site editing is currently active.
+	 */
 	function is_fse_active() {
-		$fse_enabled = Jetpack::is_plugin_active( 'full-site-editing/full-site-editing-plugin.php' );
-		$has_method  = method_exists( '\A8C\FSE\Full_Site_Editing', 'is_supported_theme' );
-		if ( $fse_enabled && $has_method ) {
-			$fse  = \A8C\FSE\Full_Site_Editing::get_instance();
-			$slug = get_option( 'stylesheet' );
-			return $fse->is_supported_theme( $slug );
+		if ( ! Jetpack::is_plugin_active( 'full-site-editing/full-site-editing-plugin.php' ) ) {
+			return false;
+		}
+		if (
+			/**
+			 * Allow disabling Full Site Editing, even when the FSE plugin is active.
+			 *
+			 * @module json-api
+			 *
+			 * @since 7.7.0
+			 *
+			 * @param bool $disable_fse Disable Full Site Editing. Defaults to false.
+			 */
+			apply_filters( 'a8c_disable_full_site_editing', false )
+		) {
+			return false;
+		}
+		$has_is_supported_theme_method = method_exists( '\A8C\FSE\Full_Site_Editing', 'is_supported_theme' );
+		$has_normalize_theme_slug      = method_exists( '\A8C\FSE\Full_Site_Editing', 'normalize_theme_slug' );
+		if ( $has_is_supported_theme_method && $has_normalize_theme_slug ) {
+			$slug = \A8C\FSE\Full_Site_Editing::get_instance()->normalize_theme_slug( get_option( 'stylesheet' ) );
+			return \A8C\FSE\Full_Site_Editing::get_instance()->is_supported_theme( $slug );
 		}
 		return false;
 	}