Using Redirect Args to Display Errors
James DiGioia
if ($error) {add_filter('redirect_post_location', function( $location ) use ( $error ) {return add_query_arg( 'my-plugin-error', $error->get_error_code(), $location );});}
add-redirect-args.php
if ( array_key_exists( 'my-plugin-error', $_GET) ) { ?><div class="error"><p><?phpswitch($_GET['my-plugin-error']) {case 'an_error_code':echo 'The post failed to save because problems.';break;case 'another_error_code':echo 'The post failed to save because reasons.';break;default:echo 'An error ocurred when saving the post.';break;}?></p></div><?php}
display-get-errors.php