SessionInterface::getFlashBag() error reported by PHP Stan

[DavidGarciaCat]

Symfony version(s) affected:

Both 4.x and 5.x

Description

Symfony cannot inject by default the Session service because it's not mapped as a service, so we need to inject the SessionInterface. However, PHP Stan reports an error when calling getFlashBag()

Call to an undefined method Symfony\Component\HttpFoundation\Session\SessionInterface::getFlashBag().

How to reproduce

Inject the SessionInterface and then call the getFlashBag() method. Finally, run vendor/bin/phpstan analyse src -l 2 for a level 2 analysis, where we should get that error message.

Possible Solution

Define the getFlashBag() method into the SessionInterface.

Alternatively, maybe you can give another option to pass this error reported by PHP Stan without adding extra annotations to ignore these lines once after another when they are in use in several services.

[jderusse]

If you call getFlashBag on a SessionInterface the issue is in your code. Not all implementation of SessionInterface provides this method.

duplicate of #20258, #11279, #10036 , #5568
and probably many others

[jderusse]

note: You can fix it by adding if ($session instance of Session) in your code.

[DavidGarciaCat]

Isn't a redundancy checking if the injected interface is an instance of the only service that (by default) implements it and is defined in the DI mapping?

[wouterj]

Nobody promises that your class will be instantiated by the Symfony DI mapping. Of course, that is the case in the normal path (and it's very likely to always be the case), but the point of static analysis is exactly to avoid issues if this unexpected situation does occur. If you don't like that, I recommend tweaking your PHPstan configuration to no longer complain about this issue (or add PHPdocs to indicate that you trust that it's always a Session instance).

[grogy]

As write doc we can use Symfony\Component\HttpFoundation\Session\Flash\FlashBagInterface as dependency. It works great 👍

[DavidGarciaCat]

Thanks, @grogy - funny thing no one mentioned it until now 😄 and I was not aware of this interface