Sorry I cannot check on my own: where does Symfony expose this class as an "api" type?
To me, this is legit as internal since all cases where TestContainer is used should be typed as ContainerInterface, preserving the actual class as an implementation detail, thus internal.

probably here

Thanks.
No issue on Symfony 's side then.

The same happens with Polyfills, for example using \IntlDateFormatter from the intl extension results in something like:

Access to constant LONG of internal class Symfony\Polyfill\Intl\Icu\IntlDateFormatter from outside its root namespace Symfony. 

Even when the intl extension is installed and the polyfill is unused.

Let me close since there's nothing to fix on this side: the code declares things the way it should.

PHPStan has to typehint KernelTestCase::getContainer() as TestContainer because it has to understand that it's okay to access private services in tests.

Some references:

• False positive in Tests: Service XY is private phpstan/phpstan-symfony#27
• Fix false positive "Service ... is private." when using KernelTestCase::$container phpstan/phpstan-symfony#210
• Followup of Symfony TestContainer issue phpstan/phpstan-symfony#212

I'm not using this part of Symfony so I can't judge who's right or wrong here. Anyone care to elaborate?

PHPStan has to typehint KernelTestCase::getContainer() as TestContainer because it has to understand that it's okay to access private services in tests.

I get that. I don't know how to solve this issue. To me this looks like something phpstan/SA tools needs to deal with somehow. If Symfony can help, sure, but making TestContainer non-internal doesn't seem appropriate to me here. It's just a class with some implementation in it. Making it a fully supported type would increase the surface of the BC promise for no good reasons. The fact this concretion is used to give access to private services is just an implementation detail from the PoV of Symfony.

@nicolas-grekas I agree with you. We need to mark the container fetched via this method somehow. Or we can allow fetching private services on all ContainerInterface when we're in KernelTestCase subclass.

@ondrejmirtes I annotated TestContainer.stub with @api, which seems to 'fix' the error. Is this an acceptable fix, or will this cause other issues?

@mickverm PHPStan doesn't interpret @api in any way for the @internal rules. You simply overridden the PHPDoc. You could have used @i-am-awesome and it would work the same way 😂

The problem with removing @internal from TestContainer in PHPStan stubs is that other usages of TestContainer that should be reported as invalid would not be reported.

The right solution is to remove these stubs altogether:

• https://github.com/phpstan/phpstan-symfony/blob/2.0.x/stubs/Symfony/Bundle/FrameworkBundle/Test/KernelTestCase.stub
• https://github.com/phpstan/phpstan-symfony/blob/2.0.x/stubs/Symfony/Bundle/FrameworkBundle/Test/TestContainer.stub

And fix this line https://github.com/phpstan/phpstan-symfony/blob/cf8c9c6994cf2a07c7aefddef2b26941d19efba1/src/Rules/Symfony/ContainerInterfacePrivateServiceRule.php#L46 with some other condition.

Solved in phpstan-symfony 2.0.6 thanks to phpstan/phpstan-symfony#441.