Fix Lazy Objects Reflection API: add ReflectionProperty::isLazy()

[arnaud-lb]

This is a bug fix for a design flaw in the Lazy Objects Reflection API:

The API provides ReflectionProperty::setRawValueWithoutLazyInitialization() and ReflectionProperty::skipLazyInitialization(), but does not provide any way to fetch the value of a property without triggering initialization, or to check if a property is lazy.

A workaround is to cast the object as array (with (array) $obj), but this is slower than needed and is used in performance-critical code in Doctrine, for instance.

This PR fixes this by adding the method ReflectionProperty::isLazy(object $obj). It returns true when the property is lazy and accessing it would trigger initialization of the object.

[beberlei]

@arnaud-lb seeing it so closely to the isInitialized method, maybe your idea with isLazy is better to avoid confusion with the initialized / uninitialized concept for readonly properties.

[bukka]

you cannot target 8.4 as we no longer allow any features in RC.

[nicolas-grekas]

I missed this in the RFC because I used a hack based on (array). Definitely something that's missing and that'd be great even late in 8.4 🙏

[arnaud-lb]

@bukka after thinking more about this change, we would like to propose it as an API bug fix since this addresses a flaw in an API introduced in 8.4.

@php/release-managers-84 do you accept this to be merged in 8.4 as a bug fix?

NB: build failures are unrelated.

[NattyNarwhal]

Since it seems a polyfill could be used and documented, I'm not sure about rushing it into 8.4. However, it's very simple, self-contained, and fixes a problem with an 8.4 specific feature (as opposed to something general that 8.4 makes more obvious), so I think it should be fine. I'm wondering what the other RMs think.

[ericmann]

Since it seems a polyfill could be used and documented, I'm not sure about rushing it into 8.4. However, it's very simple, self-contained, and fixes a problem with an 8.4 specific feature (as opposed to something general that 8.4 makes more obvious), so I think it should be fine. I'm wondering what the other RMs think.

I have no objection.

[bukka]

It's a bit questionable whether this is a bug but if others think it is, I don't have objections.