Add error handling for missing or unreadable WordPress files in core commands

src/Core_Command.php

@@ -659,7 +659,7 @@
 			add_filter( 'send_site_admin_email_change_email', '__return_false' );
 		}
 
-		require_once ABSPATH . 'wp-admin/includes/upgrade.php';
+		$this->require_upgrade_file( 'WordPress installation' );
 
 		$defaults = [
 			'title'          => '',
@@ -715,7 +715,7 @@
 	private function multisite_convert_( $assoc_args ) {
 		global $wpdb;
 
-		require_once ABSPATH . 'wp-admin/includes/upgrade.php';
+		$this->require_upgrade_file( 'multisite conversion' );
 
 		$domain = self::get_clean_basedomain();
 		if ( 'localhost' === $domain && ! empty( $assoc_args['subdomains'] ) ) {
@@ -1211,7 +1211,7 @@
 			&& ( $update->version !== $wp_version
 				|| Utils\get_flag_value( $assoc_args, 'force' ) ) ) {
 
-			require_once ABSPATH . 'wp-admin/includes/upgrade.php';
+			$this->require_upgrade_file( 'WordPress core update' );
 
 			if ( $update->version ) {
 				WP_CLI::log( "Updating to version {$update->version} ({$update->locale})..." );
@@ -1371,7 +1371,7 @@
 			}
 			WP_CLI::success( "WordPress database upgraded on {$success}/{$total} sites." );
 		} else {
-			require_once ABSPATH . 'wp-admin/includes/upgrade.php';
+			$this->require_upgrade_file( 'WordPress database update' );
 
 			/**
 			 * @var string $wp_current_db_version
@@ -1663,4 +1663,49 @@
 			WP_CLI::error( 'ZipArchive failed to open ZIP file.' );
 		}
 	}
+
+	/**
+	 * Safely requires the WordPress upgrade.php file with error handling.
+	 *
+	 * This method checks for file existence and readability before requiring,
+	 * and registers a shutdown function to catch fatal errors during file loading
+	 * (e.g., missing PHP extensions or other runtime issues).
+	 *
+	 * @param string $context Context for error messages (e.g., 'installation', 'upgrade', 'database update').
+	 */
+	private function require_upgrade_file( $context = 'WordPress operation' ) {
+		$upgrade_file = ABSPATH . 'wp-admin/includes/upgrade.php';
+
+		if ( ! file_exists( $upgrade_file ) ) {
+			WP_CLI::error( "WordPress installation is incomplete. The file '{$upgrade_file}' is missing." );
+		}
+
+		if ( ! is_readable( $upgrade_file ) ) {
+			WP_CLI::error( "Cannot read WordPress installation file '{$upgrade_file}'. Check file permissions." );
+		}
+
+		// Register a shutdown function to catch fatal errors during require_once.
+		$shutdown_handler = function () use ( $upgrade_file, $context ) {
+			$error = error_get_last();
+			if ( null !== $error && in_array( $error['type'], [ E_ERROR, E_PARSE, E_CORE_ERROR, E_COMPILE_ERROR ], true ) ) {
+				// Check if error occurred in the upgrade file or files it includes.
+				if ( false !== strpos( $error['file'], 'wp-admin/includes/' ) || false !== strpos( $error['file'], 'wp-includes/' ) ) {
+					WP_CLI::error(
+						sprintf(
+							"Failed to load WordPress files for %s. This often indicates a missing PHP extension or a corrupted WordPress installation.\n\nError: %s in %s on line %d\n\nPlease check that all required PHP extensions are installed and that your WordPress installation is complete.",
+							$context,
+							$error['message'],
+							$error['file'],
+							$error['line']
+						)
+					);
+				}
+			}
+		};
+
+		register_shutdown_function( $shutdown_handler );
+
+		// phpcs:ignore WordPressVIPMinimum.Files.IncludingFile.UsingVariable -- Path comes from WordPress itself.
+		require_once $upgrade_file;
+	}
 }