[E015] Error: cannot declare method `foo::bar` abstract, as `foo` class is not abstract
   ,-[code.php:4:28]
   |
 3 | class foo {
   *       ^^^  
   *             
 4 |     abstract function bar();
   *     ^^^^|^^^          ^^^  
   *         `------------------ try removing this `abstract` modifier
   *                            
   *                             
---'