Fixed issue between Rector and WP

rector.php

@@ -10,12 +10,6 @@
     // get parameters
     $parameters = $containerConfigurator->parameters();
 
-    // Rector relies on autoload setup of your project; Composer autoload is included by default; to add more:
-    $parameters->set(Option::AUTOLOAD_PATHS, [
-        // full directory
-        __DIR__ . '/vendor/wordpress/wordpress',
-    ]);
-
     // paths to refactor; solid alternative to CLI arguments
     $parameters->set(Option::PATHS, [
         __DIR__ . '/src',
@@ -41,4 +35,25 @@
 
     // is your PHP version different from the one your refactor to? [default: your PHP version]
     $parameters->set(Option::PHP_VERSION_FEATURES, '7.1');
+
+    // Rector relies on autoload setup of your project; Composer autoload is included by default; to add more:
+    $parameters->set(Option::AUTOLOAD_PATHS, [
+        // full directory
+        __DIR__ . '/vendor/wordpress/wordpress',
+    ]);
+
+    /**
+     * This constant is defined in wp-load.php, but never loaded.
+     * It is read when resolving class WP_Upgrader in Plugin.php.
+     * Define it here again, or otherwise Rector fails with message:
+     *
+     * "PHP Warning:  Use of undefined constant ABSPATH -
+     * assumed 'ABSPATH' (this will throw an Error in a future version of PHP)
+     * in .../graphql-api-for-wp/vendor/wordpress/wordpress/wp-admin/includes/class-wp-upgrader.php
+     * on line 13"
+     */
+    /** Define ABSPATH as this file's directory */
+    if (!defined('ABSPATH')) {
+        define('ABSPATH', __DIR__ . '/vendor/wordpress/wordpress/');
+    }
 };

src/Plugin.php

@@ -37,6 +37,7 @@
 use GraphQLAPI\GraphQLAPI\Blocks\AccessControlRuleBlocks\AccessControlDisableAccessBlock;
 use GraphQLAPI\GraphQLAPI\ModuleResolvers\SchemaConfigurationFunctionalityModuleResolver;
 use GraphQLAPI\GraphQLAPI\Blocks\AccessControlRuleBlocks\AccessControlUserCapabilitiesBlock;
+use WP_Upgrader;
 
 class Plugin
 {
@@ -152,20 +153,12 @@ function () use ($isPluginJustActivatedOptionName): void {
 
     /**
      * This function runs when WordPress completes its upgrade process
-     * If this plugin is updated, it sets a transient flag.
-     *
-     * Use `object` as param type for $upgrader_object, instead of the
-     * more specific `WP_Upgrader`, because Rector fails with it:
-     *
-     * "PHP Warning:  Use of undefined constant ABSPATH -
-     * assumed 'ABSPATH' (this will throw an Error in a future version of PHP)
-     * in /home/travis/build/GraphQLAPI/graphql-api-for-wp/vendor/wordpress/wordpress/wp-admin/includes/class-wp-upgrader.php
-     * on line 13"
+     * If this plugin is updated, it sets a transient flag
      *
      * @param array<string, mixed> $options
      * @see https://codex.wordpress.org/Plugin_API/Action_Reference/upgrader_process_complete
      */
-    public function checkIsPluginUpgraded(object $upgrader_object, array $options): void
+    public function checkIsPluginUpgraded(WP_Upgrader $upgrader_object, array $options): void
     {
         // If an update has taken place and the updated type is plugins and the plugins element exists,
         // or an install of a new version of the plugin