Add valid checks slug array and warning for non-existent checks

includes/Checker/Abstract_Check_Runner.php

@@ -461,6 +461,7 @@
 	 */
 	final public function get_checks_to_run() {
 		$check_slugs = $this->get_check_slugs();
+		$check_slugs = $this->return_valid_check_slugs( $check_slugs );
 		$check_flags = Check_Repository::TYPE_STATIC;
 
 		// Check if conditions are met in order to perform Runtime Checks.
@@ -489,6 +490,30 @@
 		return $collection->to_map();
 	}
 
+	/**
+	 * Returns an array of valid check slugs.
+	 *
+	 * @since 1.0.1
+	 *
+	 * @param array $check_slugs An array of check slugs to be run.
+	 *
+	 * @return array An array of valid check slugs.
+	 */
+	protected function return_valid_check_slugs( array $check_slugs ) {
+
+		$available_checks_slugs = array_keys( $this->check_repository->get_checks( Check_Repository::TYPE_ALL )->to_map() );
+
+		foreach ( $check_slugs as $slug ) {
+			if ( ! in_array( $slug, $available_checks_slugs, true ) ) {
+				echo 'Warning: Check with the slug "' . $slug . '" does not exist.' . PHP_EOL;
+				$key = array_search( $slug, $check_slugs, true );
+				unset( $check_slugs[ $key ] );
+			}
+		}
+
+		return $check_slugs;
+	}
+
 	/**
 	 * Checks whether the current environment allows for runtime checks to be used.
 	 *

readme.txt

@@ -83,6 +83,7 @@ In any case, passing the checks in this tool likely helps to achieve a smooth pl
 
 = 1.0.2 =
 
+* Enhancement - Show a warning if a non-existent check if passed to the WP CLI --checks argument. (issue 348)
 * Feature - New `Enqueued_Scripts_Scope_Check` (`enqueued_scripts_scope`), `Enqueued_Styles_Size_Check` (`enqueued_styles_size`) and `Enqueued_Resources_Check` (`enqueued_resources`) performance checks.
 * Enhancement - Improved readme check and added a new `wp_plugin_check_ignored_readme_warnings` filter.
 * Enhancement - New `wp_plugin_check_default_categories` filter to change the categories which are selected by default.