Duplicate of #10036 #5568. See @Drak's explanation here: #5568 (comment)

Correct, but they are closed while it's still an issue.

Possible solution? Create a FlashAwareSessionInterface that extends the SessionInterface but also has the getFlashBag for example.

Edit: getBag('flashes') isn't 100% safe either.

@fabpot you might possibly be interested, I've solved my problem like this:

services:
    session.flash_bag:
        class:           Symfony\Component\HttpFoundation\Session\FlashBagInterface
        factory_service: session
        factory_method:  getFlashBag

This has the following benefits:

• You can inject it, even if you have no request/session available
• You don't need to know the flashbag name to do Request::getSession()::getBag('flashes') as the name can change
• If a different bag is used in the session, you won't use the wrong one by accident
• You don't have to inject the Session in order to get the FlashBag

It might not really go well with: #11315 because it's an interface typehint. But that should be fixable.

This change should not have any BC issues,

Closing this issue as it seems like it's not a priority to fix as a work-around is available.

it looks like this is still an issue