PHP error in WordPress backend wrapped as native notice. Refer/screenshot on https://core.trac.wordpress.org/ticket/35155

php-error-in-wp.php

<?php

/*
  Plugin Name: Error For WP backend
  Plugin URI: https://github.com/Mte90/
  Description: Wrap the PHP errors in the WP admin backend with the native notice
  Author: Mte90
  Version: 1.0.0
 */

if(! function_exists( 'wp_error_handler' )) {
  set_error_handler( "wp_error_handler" );
  
  function wp_error_handler( $errno, $errstr, $errfile, $errline ) {
    if ( !(error_reporting() & $errno) ) {
      // This error code is not included in error_reporting
      return;
    }
    $err = '';
    // If admin wrap the PHP error
    if ( is_admin() ) {
      $err = "<div class='message error' style='clear:both'><p>PHP ";
    }
    // Else wrap the code like the classic errors
    if ( $errno === 1024 || $errno === 8 ) {
      $err .= '<b>Notice</b>';
    } elseif ( $errno === 512 || $errno === 2 ) {
      $err .= '<b>Warning</b>';
    } elseif ( $errno === 256 || $errno === 9191 ) {
      $err .= '<b>Error</b>';
    }
    $err .= ': ' . $errstr . ' In <b>' . $errfile . '</b> on line <b>' . $errline . '</b>';
    if ( is_admin() ) {
      $err .= '</p></div>';
    }
    echo $err;
  }
}

// Simulate PHP errors
// Remove that to use
add_action( 'plugins_loaded', 'generate_error_example' );

function generate_error_example() {
  get_currentuserinfo();
  array_merge( 1, array() );
}

I discovered that if you wrap this in if(!function_exists('wp_error_handler')) {} it results in the following error:

set_error_handler() expects the argument (wp_error_handler) to be a valid callback

Moving set_error_handler() after the function declaration prevents this problem.

improved the code, sorry but gist don't have notifications -.-'

what is errno 9191 ???