react-test-renderer shallow: SFCs should not get `this`

[ljharb]

Do you want to request a feature or report a bug?
bug.

What is the current behavior?
This addresses a bug in enzyme, enzymejs/enzyme#1683.

On this line element.type() invokes the SFC with element as the this value. I believe that this is needed for create-react-class components, but that there needs to be a separate branch for SFCs.

What is the expected behavior?
this inside a strict-mode SFC will be undefined, not the element.

Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?
In all of React 0.13, 0.14, 15, and 16, this bug exists.

While the bug ideally will be fixed, I understand that it's highly unlikely that it would be backported to the 14/15 lines - but I can wrap around it if there's a reliable way, in those versions, to distinguish SFCs from create-react-class components (is there?).

[gaearon]

If something doesn't have .prototype or .prototype.isReactComponent, we won't try to new it.

(This still doesn't mean it's functional — it could return an object with a render method — but at least it shouldn't have this.)

Happy to take a fix for 16.x.

[ljharb]

So both class and createReactClass components will have .isReactComponent on them? Is there a spec on providing a receiver to other things, or is my assumption correct that unless it’s newed, it should lack a receiver?