Improve error clarity when BindingResolutionException leads to “headers already sent” #56286
Description
Laravel Version
11
PHP Version
8.3
Database Driver & Version
No response
Description
When a class fails to resolve due to a typo or missing import (e.g., BindingResolutionException), Laravel attempts to render a 500 response. However, if output has already started (e.g., a PHP fatal error from Composer autoload), this results in a generic PHP error:
"Cannot modify header information - headers already sent by ... "
This masks the real root cause and makes debugging significantly harder.
Expected behavior:
Laravel should show the original exception that caused the failure — not just the secondary “headers already sent” error.
Steps To Reproduce
Example scenario:
define some valid route with some controller:
in controller:
use App\DTOs\Auth\GetUsersDTO; // incorrect namespace
This causes class autoload to fail -> fatal error is output -> Laravel tries to send a response -> PHP throws "headers already sent".