Compiled DI and Developer DI Are Sometimes Incompatible

[maxbucknell]

Preconditions

I have found that there are some cases where classes will be introspected by Reflection in the Developer mode, but will not be caught by the setup:di:compile command. This increases the testing burden of developers, and produces some very difficult to understand error messages.

As far as I know, this affects every version of Magento 2.0 and 2.1, but I was using 2.0.8 at the time. The environment is modern and following all best practices, and was replicated across a variety of environments.

Steps to reproduce

1. Inject an automatically generated factory of a non-injectable class that is not part of a Magento module. We were using the Facebook\Facebook class from the facebook/graph-sdk Composer package.

2. Run the code with the Developer Mode DI, and it will generate the factory, using the Object Manager. The Object Manager will dynamically use Reflection to inspect which arguments are required, and match them all up. It works like a dream.

3. Run the code with the Compiled DI, and it generates the factory, and calls the Object Manager in the same way. However, the Facebook\Facebook class is not in the compiled DI information, and the Object Manager will pass in the default constructor arguments, which is just the Object Manager.

4. The result is some kind of type error. In my case, it was:

   Uncaught TypeError: Argument 1 passed to Facebook\Facebook::__construct()
   must be of the type array, object given```
   

Expected result

I'm not 100% sure what the correct thing to do here is. If we accept that the behaviour should at least be consistent, our options are to prevent the Developer DI from working with external classes (which I don't like), or to enhance the Compiled DI so that it works with external classes that are referred to through generated classes (I like this one more).

A compromise might be to document it well, or something.

Fix

For anyone stumbling across this issue, it can be fixed by adding an empty class to your module, and having it extend your external class. Tell Anton Kril that I found a use for inheritance.

If you generate a factory for this class in your module, it will find the parent constructor arguments without issue. You can add a preference into di.xml for Facebook\Facebook, to be My\Module\Model\Facebook, and everything else just falls into place.

[antonkril]

Nice try, but composition would work here too ;)

We discussed this issue, and the resolution is to add fallback to reflection in compiled mode.

[kandy]

Internal ticket to track MAGETWO-51176

[maxbucknell]

Can I have a status update on this? If it hasn't been worked on, I'd like to take it up.

CC @maksek

[igortregub]

I've had the same issue. Have you any updates about it?

[attilai]

Same issue

[mcspronko]

@antonkril Can you please tell me how composition will help to solve the issue? I am having class A where one argument into __construct() method is passed. I use this class A to inject into MagentoClass B and having same error. Thanks for advice.

[maghamed]

@mcspronko @maxbucknell

We made a fix in 2.2.0 for this case
8498e12
(lib/internal/Magento/Framework/ObjectManager/Config/Compiled.php)

but we still state that Compiler may not be able to resolve all dependencies on 3rd party classes. That’s why 3rd party classes should not be injected in the constructor of Magento classes, instead, they should be instantiated via new operator, preferably in adapters only.

Third party (3P) libs don't mean third party libraries that are actually registered with ComponentRegistrar as components of type "library," it means generic php libraries that are not special Magento application components. So this is about unregistered 3P libraries.

[magento-engcom-team]

@maxbucknell, thank you for your report.
The issue is already fixed in 2.2.0