use Twig 2.7 namespaces

[IonBazan]

Q	A
Bug fix?	no
New feature?	yes
Doc updated	no
BC breaks?	yes
Deprecations?	no
Tests pass?	yes
Fixed tickets	-
License	MIT

Twig 2.7 moved to namespaced classes instead of old pre-PHP5.3 ones.

[IonBazan]

I think there is a problem with Travis-CI config - the test is shown as passed, but it contains errors: https://travis-ci.org/schmittjoh/serializer/jobs/506178733. Although, it's not caused by this PR.

[goetas]

Hi, Thanks for the PR.

Currently I think that is not a good idea to drop Twig 1.x and <2.7 support. C

Can this changes be done in a backward compatible way, preferring the new class names if they are available, and falling back on the old if they are not available?

[enumag]

This doesn't necessarily break compatibility with all versions <2.7. Namespaced aliases existed several versions before that, 2.7 only added the deprecation of non-namespaced types.

Btw. not supporting Twig 2.7 is quite a problem now because roave/security-advisories no longer allows Twig 2.0-2.6 because of this vulnerability.

[mbabker]

Can this changes be done in a backward compatible way, preferring the new class names if they are available, and falling back on the old if they are not available?

If the version constraint is set to ~1.34|~2.4 then you're OK, those were the two releases where the namespaced aliases were introduced.

[goetas]

Having ~1.34|~2.4 is ok for me

[goetas]

Thanks!