Arrow function vs require_once

[zboszor]

Description

The following code:

retfunc.php

<?php
return array('a', 'b');

test-loadfile.php

<?php
$path = 'retfunc.php';
$i = 1;
$data = (fn () => require_once $path)();
while (is_array($data)) {
    $i++;
    $data = (fn () => require_once $path)();
    if ($i > 100)
        break;
}

if (!is_array($data)) {
    echo 'not an array in round ' . $i . PHP_EOL;
    var_dump($data);
} else
    echo 'success' . PHP_EOL;

Resulted in this output:

$ php test-loadfile.php
not an array in round 2
bool(true)

But I expected this output instead:

$ php test-loadfile.php
success

This is a minimal example that mimics Laravel's laravel/framework/src/Illuminate/Foundation/Bootstrap/LoadConfiguration.php that loads configuration files.

Maybe it's an undocumented corner case, but require_once should return the file source the second and subsequent times without actually loading the file again, so the arrow function would produce the array value.

The example code works if both arrow functions use require.

PHP Version

PHP 8.4.8 (cli) (built: Jun  3 2025 16:29:26) (NTS gcc x86_64)
Copyright (c) The PHP Group
Built by Fedora Project
Zend Engine v4.4.8, Copyright (c) Zend Technologies

Operating System

Fedora 42

[nielsdos]

Smaller repro:

x.php:

<?php return [];

y.php

<?php
var_dump(require_once 'x.php');
var_dump(require_once 'x.php');

Executing y.php yields:

array(0) {
}
bool(true)

It seems like a deliberate design choice to make it return true on subsequent requires. Changing this behaviour is a language change. Furthermore, this would be a BC break.
Therefore, changing this behaviour requires an RFC.