Crash when using print statement inside closure in Concurrency Facade

[rcalicdan]

Laravel Version

12.28.1

PHP Version

8.4.5

Database Driver & Version

No response

Description

When using Laravel’s Concurrency::run() feature, the process crashes with Trying to access array offset on null in ProcessDriver.php if a closure contains echo or print. This happens because child processes communicate back to the parent via JSON, and printing to STDOUT corrupts the expected JSON payload, causing $result to become null. Instead of crashing, Laravel should either gracefully handle extra output, redirect it, or clearly document that closures should not use direct output and should return values or use logging instead. Please take a look at this critical architectural flaw.

Steps To Reproduce

`<?php

use Illuminate\Support\Facades\Concurrency;
use Library\Defer\Parallel;

require "vendor/autoload.php";
$app = require "bootstrap/app.php";
$kernel = $app->make(Illuminate\Contracts\Console\Kernel::class);
$kernel->bootstrap();

$start1 = microtime(true);
Concurrency::run([
function () {
sleep(1);
echo "Task 1 done";
},
function () {
sleep(2);
echo "Task 2 done";
},
function () {
sleep(3);
echo "Task 3 done";
},
]);
$end1 = microtime(true);
echo 'Concurrency time: ' . ($end1 - $start1) . " seconds\n";
`

`C:\Laravel\test-herd>php test.php

ErrorException

Trying to access array offset on null

at vendor\laravel\framework\src\Illuminate\Concurrency\ProcessDriver.php:51
47▕ }
48▕
49▕ $result = json_decode($result->output(), true);
50▕
➜ 51▕ if (! $result['successful']) {
52▕ throw new $result['exception'](
53▕ ...(! empty(array_filter($result['parameters']))
54▕ ? $result['parameters']
55▕ : [$result['message']])

1 vendor\laravel\framework\src\Illuminate\Concurrency\ProcessDriver.php:51
Illuminate\Foundation\Bootstrap\HandleExceptions::{closure:Illuminate\Foundation\Bootstrap\HandleExceptions::forwardsTo():257}("Trying to access array offset on null", "C:\Laravel\test-herd\vendor\laravel\framework\src\Illuminate\Concurrency\ProcessDriver.php")

2 vendor\laravel\framework\src\Illuminate\Collections\Arr.php:803
Illuminate\Concurrency\ProcessDriver::{closure:Illuminate\Concurrency\ProcessDriver::run():44}()
`