Fatal error during autoloading of complex inheritance chain with LSP checks since PHP 8.1.0

Description

The following code:

<?php

$depth = 0;

spl_autoload_register(function ($class) use (&$depth) {
    $depth++;
    $indent = str_repeat('| ', $depth);
    echo $indent."$depth: $class\n";

    if ($class == 'IFace') {
        interface IFace {}
    } elseif ($class == 'IFaceImplementor') {
        class IFaceImplementor implements IFace {}
    } elseif ($class == 'InterfaceOfMainParent') {
        interface InterfaceOfMainParent
        {
            public function methodForSecondaryLspCheck(): IFace;
        }
    } elseif ($class == 'MainParent') {
        abstract class MainParent implements InterfaceOfMainParent
        {
            public function methodForSecondaryLspCheck(): IFaceImplementor {}
        }
    } elseif ($class == 'Intermediate') {
        abstract class Intermediate extends MainParent {}
    } elseif ($class == 'Child1') {
        class Child1 extends Intermediate {}
    } elseif ($class == 'Child2') {
        class Child2 extends Intermediate {}
    } elseif ($class == 'EntrypointParent') {
        abstract class EntrypointParent
        {
            abstract public function methodForLspCheck1(): MainParent;
            abstract public function methodForLspCheck2(): MainParent;
        }
    } elseif ($class == 'Entrypoint') {
        class Entrypoint extends EntrypointParent
        {
            public function methodForLspCheck1(): Child1 {}
            public function methodForLspCheck2(): Child2 {}
        }
    }

    $depth--;
});

class_exists(Entrypoint::class);

Resulted in this output:

| 1: Entrypoint
| | 2: EntrypointParent
| | 2: Child1
| | | 3: Intermediate
| | | | 4: MainParent
| | | | | 5: InterfaceOfMainParent
| | | | | 5: Child2

Fatal error: During inheritance of MainParent, while autoloading Child2: Uncaught Error: Class "Intermediate" not found in php-wasm run script:29
Stack trace:
#0 php-wasm run script(20): {closure}('Child2')
#1 php-wasm run script(25): {closure}('MainParent')
#2 php-wasm run script(27): {closure}('Intermediate')
#3 php-wasm run script(37): {closure}('Child1')
#4 [internal function]: {closure}('Entrypoint')
#5 php-wasm run script(47): class_exists('Entrypoint')
#6 {main} in php-wasm run script on line 20

But I expected this output instead:

| 1: Entrypoint
| | 2: EntrypointParent
| | 2: Child1
| | | 3: Intermediate
| | | | 4: MainParent
| | | | | 5: InterfaceOfMainParent
| | | | | 5: IFaceImplementor
| | | | | | 6: IFace
| | 2: Child2

• Full reproduction repository: https://github.com/janedbal/php-bug-complex-inheritance-chain-autoloading
• 3v4l version: https://3v4l.org/G5fFe
• Broken since: PHP 8.1.0

PHP Version

PHP 8.5.0RC1 (cli) (built: Oct  8 2025 22:41:41) (NTS)
Copyright (c) The PHP Group
Built by https://github.com/docker-library/php
Zend Engine v4.5.0RC1, Copyright (c) Zend Technologies
    with Zend OPcache v8.5.0RC1, Copyright (c), by Zend Technologies

Operating System

No response

Bắt đầu với repository tái hiện và entry point class_exists(Entrypoint::class), sau đó so sánh autoload trace trên PHP 8.1.0 và các phiên bản mới hơn. Điều tra chuỗi kế thừa và kiểm tra LSP được thể hiện trong issue. Được coi là hoàn tất khi bản tái hiện hoàn thành mà không có fatal error và tạo ra thứ tự autoload như mong đợi.