Remove zend json from data object

[dmanners]

Description

The DataObject class has a method toJson that uses Zend_Json. Since this at EOF we should replace the usage. Unfortunately in this case that is not so "simple" after some discussion with @okorshenko it was decided to create a new static class for this single case. This should not be used in other places but for this case it is "ok".

Fixed Issues (if relevant)

1. Upgrade ZF components. Zend_Json #9236: Upgrade ZF components. Zend_Json

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[ihor-sviziev]

@dmanners Why do we need new object with static method? We could add to constructor optional parameter (with fallback to object manager)

[dmanners]

@ihor-sviziev I am more than happy to find another option but unfortunately going the route of adding an optional dependency causes big breaks in the test suite. I am not sure exactly how the object manager changes in the test suite so there could be an option to mock the fallback during the test suite.

[orlangur]

Why do we need to add new behavior with @throws \InvalidArgumentException instead of just calling json_encode?

What do you think about deprecating toJson method also to decrease amount of DataObject class responsibilities?

[okorshenko]

Hi @orlangur removing the method from DataObject interface will be BiC that we would like to avoid. The standard approach for adding new dependencies to DataObject does not work well due to modularity. So we suggested the way that @dmanners implemented.

[dmanners]

@orlangur normally I would like to keep away from the direct calls to json_encode but in the case of this class with the combination of the deprecation of the toJson I think I could live with myself. This class itself needs a lot of love or at least the usages of this class need some love and care so highlighting that is not a bad thing in my books. What do you think @okorshenko

[orlangur]

@okorshenko I did not say a word regarding method removal, just deprecation. As to me static class introduction with comment to use it in only one place is much uglier than simply using json_encode in this place (the only difference compared to serializer https://github.com/magento/magento2/blob/develop/lib/internal/Magento/Framework/Serialize/Serializer/Json.php#L24 is not throwing an exception which corresponds to old method behavior).

[korostii]

Hi @okorshenko
As @orlangur says, there's nothing wrong with both keeping the method present and avoiding new dependencies.
However, what's the point of using \Magento\Framework\Serialize\JsonConverter instead?

After all, the new @throws declaration a BiC change by itself.
How is it any better than using json_encode directly?