Infinite recursion with test doubles in combination with a destructor about phpunit

[matthewjumpsoffbuildings]

I am seeing this issue when running unit tests in Laravel, with my test classes extending Illuminate\Foundation\Testing\TestCase

Is it likely that the base Laravel class incorrectly handles self-references and destructors similar to #5809 (comment), and that is the cause of the segfaults I am seeing? Laravel has a ton of methods that return $this, and none of my own tests I am adding on top of the base Laravel test classes create stubs or test self-return, so it seems like the most likely location of the issue is within the base Laravel class no?

[sebastianbergmann]

Thank you, @nielsdos, for investigating this.

I have stripped down the reproducer:

composer.json

{
  "require-dev": {
    "phpunit/phpunit": "^10.5"
  },
  "autoload": {
    "classmap": [
      "src/"
    ]
  }
}

src/Example.php

<?php declare(strict_types=1);
class Example {
    public function methodWithSelfReferenceReturn(): self
    {
        return $this;
    }

    public function __destruct()
    {
        $this->methodWithSelfReferenceReturn();
    }
}

tests/ExampleTest.php

<?php declare(strict_types=1);
use PHPUnit\Framework\TestCase;

final class ExampleTest extends TestCase
{
    public function testOne(): void
    {
        $this->createStub(Example::class);
    }
}

$ php-82 ./vendor/bin/phpunit --no-configuration --do-not-cache-result tests 
PHPUnit 10.5.17 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.2.19-dev

[1]    327489 segmentation fault (core dumped)

[sebastianbergmann]

Here is what happens in #5809 (comment):

• createStub() creates a test stub for Example (the destructor of Example is not stubbed)
• The destructor of Example is invoked
• The destructor of Example calls methodWithSelfReferenceReturn()
• The return value generator is called to generate a return value as no return value was configured for methodWithSelfReferenceReturn() on the test stub
• The return value generator looks at the return type declaration for methodWithSelfReferenceReturn(), sees self, resolves self to Example, and creates a new test stub for Example
• And now the infinite recursion starts ...

There is no bug here, though.

The return type declaration self "only" means that an object of the same type is to be returned. It does not mean "self reference".

If you configure methodWithSelfReferenceReturn() on the test double to return a self reference (see below) then the return value generator does not get involved by the invocation handler and there will be no infinite recursion.

tests/ExampleTest.php

<?php declare(strict_types=1);
use PHPUnit\Framework\TestCase;

final class ExampleTest extends TestCase
{
    public function testOne(): void
    {
        $stub = $this->createStub(Example::class);

        $stub
            ->method('methodWithSelfReferenceReturn')
            ->willReturnSelf();
    }
}

[nielsdos]

Thanks for the great explanation!

[sebastianbergmann]

@matthewjumpsoffbuildings Please raise this question with the vendor of your framework.

[eleftrik]

@matthewjumpsoffbuildings Take a look: laravel/framework#51046 (comment)