Add getFlashBag method to Session interface.

[Aliance]

Q	A
Branch?	2.8
Bug fix?	yes
New feature?	no
BC breaks?	probably yes
Deprecations?	no
Tests pass?	?
Fixed tickets	–
License	MIT
Doc PR	–

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Now, the PHPDoc of Request::getSession method said that it returns the SessionInterface. But the
Session, getting from the Request in WebProfilerBundle uses getFlashBag method, which IDE marks as suspicious (because SessionInterface does knows nothing about it).
So I decided to add that method to symfony Session interface, but mb I should do it at WebProfilerBundle?

Is this change BC or not? I do not sure, someone could implement the session interface, so this will be a BC for them.

[stof]

Adding a method in an interface is a BC break. So it cannot be done in a minor version.

btw, you opened the PR to master while saying you want it in 2.8. But this does not change the fact about the BC break anyway

[Aliance]

btw, you opened the PR to master while saying you want it in 2.8.

My bad, fixed the base branch.

[Aliance]

So it cannot be done in a minor version.

What do you mean? This should be done only for 3.2 and higher?

[chalasr]

@Aliance adding a new method to an interface means that any class currently implementing it will break, that's not a backward compatible change. BC breaks are allowed on major versions only (the next one being 4.0 which cannot be targeted until releasing symfony 3.4 so that master becomes the 4.0 development branch) but should be avoided as possible.

[Aliance]

Ok, I understand. So what can you recommend for fixing PHPDoc issue in WebProfilerBundle?

[chalasr]

@Aliance I think the right way to make IDEs happy would be to check that the Request::getSession() return value is an instance of Session before calling getFlashBag on it since the SessionInterface does not guarantee this method (and I'm not sure it should, session can live without flashbag).
But I don't know if we want to go this way nor to care about that at all, see #12420 which has been rejected for the very same change.

[Aliance]

Thanks everyone!