symfony: [PhpUnitBridge] not compatible with latest phpunit

I tried to use phpunit-bridge with latest phpunit (^6.0@dev, will be stable next month), it does not work due to changes in phpunit itself.

Error: Class 'PHPUnit_Util_ErrorHandler' not found.

Since phpunit (at last) switched to namespaces, the current class is PHPUnit\Util\ErrorHandler, not PHPUnit_Util_ErrorHandler any more.

I see that supporting this is a BC break, so maybe we could provide a compatibility layer to old phpunit?

About this issue

While at lunch 😄 I got an other idea about a different approach to solve this issue:

Create classes inside the Symfony\Bridge\PhpUnit\Compat namespace with same name of PHPUnit 6 classes
- Example: \PHPUnit_Util_ErrorHandler AKA PHPUnit\Util\ErrorHandler becomes Symfony\Bridge\PhpUnit\Compat\Util\ErrorHandler
The compat classes will just have the necessary dark magic to extend the right class (I was thinking about use statements wrapped inside an if (class_exist), feel free to suggest other approaches)
The compat classes will be already deprecated and dropped in 4.0
All usages of PHPUnit classes are replaced by those compat classes
- Example: \PHPUnit_Util_ErrorHandler::handleError(...); is replaced by ErrorHandler::handleError(...); plus use Symfony\Bridge\PhpUnit\Compat\Util\ErrorHandler;

Advantages:

the changes to the code are simple and they are the same as to moving to PHPUnit 6, apart from the use statement
The git diff now will be minimal and understandable
The git diff later (4.0) will be even smaller, with the deletion of all the compat classes and just a lot of changes to the use statements: use Symfony\Bridge\PhpUnit\Compat\* to use PhpUnit\*

Just a quick update to notice that phpunit 6 is now stable.

I guess it shouldn’t be too hard to make the bridge compatible with PHPUnit 6. I try to look into it tonight.