Remove Symfony6 support

[theofidry]

I'm having too much of a hard time in #1765. The root of the issue is:

• Symfony6 was introduced in Allow Symfony 6 #1606 but without tests
• Symfony6 was actually never executed ever in the Infection CI, so any issue raised was missed
• There is signature incompatibilities between Symfony5 and Symfony6, which is a problem for code such as DummyFileSystem (fatal error kind of problem – so any autoloading of the file is breaking things hard)

I think we'll have to either review a few usages, assuming we can make it work, or drop Symfony5 support in the next version.

Meanwhile however I think it's best to (temporarily) disallow Symfony6 to allow to bump the minimum required PHP version to 8.1.

[sanmai]

What's the cost of dropping Symfony 5?

[theofidry]

5.4 is an LTS so it will be around for a while, hence I'm not too happy about dropping it. But I also don't really see a way at the moment.

That said, there is this PR and the 8.1 upgrade to do first, maybe someone can find a way to make it work once we are done with that.

[sidz]

I don't see a reason to drop symfony 6 support. Instead we need to run testsuites against symfony 6 and fix all possible cases.
I suppose we won't release new Infection version without symfony 6 and than reintroduce it.

[theofidry]

I don't see a reason to drop symfony 6 support. Instead we need to run testsuites against symfony 6 and fix all possible cases.

Because I can't make it work 😅

You can check #1765 which attempted to do that. There's been several back & forth. So either someone else give it a stab and succeeds, or we accept this PR and move incrementally in another direction, or this gets stuck for a while. What is clear is that bumping to 8.1 as the min-requirement cannot be done in one go due to a lot of broken jobs in the CI.

[theofidry]

Just to clarify in case it is misunderstood: when I talk of removing and adding back for Symfony6 I mean for the next release, not in a distant future.

[sidz]

Could you please check my comment in #1765 (comment) ?

[theofidry]

@sidz I did fix it; might need to double check though

[theofidry]

Closing this as we have both #1765 and #1775 attempting to fix it directly, and #1786 drafting another way that would make it easier to bump PHP without bumping Symfony, i.e. allowing #1765 to carry one without the Symfony6 issue being a blocker.