Add Closure and Arrow Function detection

[dlundgren]

This should fix #1535.

[Ocramius]

I think the patch is fine, but I'm not 100% sure if we should return closures at all, as described in #1535.

WDYT, @asgrim, @kukulich?

Should closures be part of the iterated-upon sources? Is this going to cause downstream regressions? 🤔

[asgrim]

IMO think it should be fine; the only thing I'd ask for is a test to show closures/arrow functions within a class method, or even within another function, are returned. Definitely would want to check @kukulich 's thoughts too in case this impacts phpstan however.

[dlundgren]

Thanks for reviewing this.

Since I hadn't thought about adding a test from within a class, when I added the following tests, they passed...

<?php class foo { function foo() { fn() => "foo"; } }
<?php class foo { function foo() { $this->test(fn() => "foo"); } }
<?php class foo { function foo() { $this->test(function() { return "foo"; }); } }

However, when I ran the change against the directory I'm working with, the ReflectionFunction had no idea that the closure was within a class, or even a method parameter. Without knowing this information, at least for my use case, I'm not sure if this change makes sense.

I'm happy to add the tests in this comment if this is still wanted.

[ondrejmirtes]

Hi, what is this going to change for users of BR? How is this going to change what Reflector returns from reflectFunction? What is the name of these anonymous functions? Is it even unique?