Enforce code style more strictly

[phavekes]

This issue is imported from pivotal - Originaly created at Oct 15, 2019 by Michiel Kodde

The last couple of PR reviews, we had some discussion about enforcing thecode style. See some tasks below.

[phavekes]

For typehint annotations we could use:
https://github.com/slevomat/coding-standard (bstrooband - Oct 15, 2019)

[phavekes]

I think we should take into account that the typehints could be needed by external libraries (i.e. doctrine) (bstrooband - Oct 15, 2019)

[phavekes]

@bstrooband I think Doctrine only relies on it\'s annotations if you choose to use Doctrine with annotations. Or do they rely on other type hints? If so I\'m most interested in a link to the documentation. (Michiel Kodde - Oct 15, 2019)

[phavekes]

Experimented with Slevomat CS rules. I added these rules to the phpcs.xml

    <rule ref="SlevomatCodingStandard.TypeHints.TypeHintDeclaration" />
    <rule ref="SlevomatCodingStandard.TypeHints.UselessConstantTypeHint" />
    <rule ref="SlevomatCodingStandard.TypeHints.DeclareStrictTypes" />
    <rule ref="SlevomatCodingStandard.TypeHints.NullableTypeForNullDefaultValue" />

That resulted in a nice set of required changes in the src folder. Many of these can be addressed automatically via phpcbf. But this results in a non-functional set of changes. As some type hints are not correctly set on interfaces/implementations of interfaces.

Bottom line is: in order to use PHP 7 type hints on the existing code. We should update the existing code to use type hints correctly. (Michiel Kodde - Oct 21, 2019)

[phavekes]

Created a branch that addresses some of the tasks of this story
https://github.com/OpenConext/OpenConext-engineblock/tree/feature/improve-cs

The todo on this branch is to implement PHP 7 strict types and type definitions on all classes. This is a change that should not be taken lightly. As increasing the strictness of the application might lead to unexpected errors/issues. (Michiel Kodde - Oct 21, 2019)