Mark doctrine/annotations dependency as optional

[greg0ire]

Now that the ORM has a driver based on PHP attributes, it seems less
necessary to require doctrine/annotations. In fact, that could also be
considered true before since there are already other drivers than the
annotation driver.
Fixes #195

[greg0ire]

Cc @javiereguiluz 🙂

[alexislefebvre]

If we upgrade from 2.2.4 to 2.3.0, doctrine/annotations is not installed anymore. So that Doctrine\Common\Annotations\AnnotationReader is not available anymore. Is it a BC break or a weak dependency in the projects that relied on AnnotationReader through doctrine/persistence?

Here is how I fixed that issue in one project: https://github.com/liip/LiipTestFixturesBundle/pull/170/files

[derrabus]

If your project relies on Doctrine Annotations for metadata mapping, adding the explicit dependency is the way to go.

[derrabus]

Related: doctrine/orm#9452

[alexislefebvre]

Thanks, so I wonder how AnnotationReader can be available here in FrameworkBundle when doctrine/annotations is only a dev dependency

Update: my bad, it's a dev dependency since Symfony 4.4 at least, so this is not related to this PR.

[derrabus]

A use statement alone does not require the referenced class to exist.

[alexislefebvre]

I'll have to investigate on Symfony's side, but I ended up with a annotations.reader service that was missing because Doctrine\Common\Annotations\AnnotationReader was not installed.

[derrabus]

Yes. If the library is missing, Symfony won't create that service. But let's not flood this PR with chat messages. Feel free to open a discussion on either board, if you have further questions:

• https://github.com/symfony/symfony/discussions
• https://github.com/doctrine/orm/discussions