Mongodb-odm: [2.0] Add PHPStan

[alcaeus]

From the documentation:

PHPStan focuses on finding errors in your code without actually running it. It catches whole classes of bugs even before you write tests for the code.

[malarzm]

I was lately playing with PHPStan and running it against ODM was also on my list :+1:

[carusogabriel]

@alcaeus Can I PR it? :innocent:

[malarzm]

@carusogabriel feel free, I'm in the middle of setting up new computer (and seeing if I can run MongoDB on that funky linux in Windows 10 :P )

[carusogabriel]

As I'm new to PHPStan, just a question: by [2.0] Add PHPStan means require it in dev-dependencies and work on phpstan.neon?

[malarzm]

My roadmap was:

1. Add it to require-dev and configure if needed (can take a look at ORM)
2. Get to a decent (5?) level without errors (at least 1 commit per level to ease review)
3. Take a page from ORM's playbook and add PHPStan to travis

[alcaeus]

Level 1 and parts of level 2 added in #1714.

[carusogabriel]

@alcaeus @malarzm May we add https://github.com/phpstan/phpstan-strict-rules or better to increase PHPStan level first?

[malarzm]

Problem with increasing levels is typehinting Common's metadata (as per interface) and expecting our own implementation. I'm :-1: for adding ifs but maybe assert would be the way to go?

[carusogabriel]

Gonna try tonight to increase one more level :smile:

[malarzm]

Closing, we're on level 7 for now :)