Ban non-void return from __construct, __destruct, __clone?

[fredemmott]

I've found one case of this in Facebook:

class Foo {
  public function __clone(): Foo {
    return new Foo( ... );
  }
}

This looks like a misunderstanding about how __clone works, as it's called after a copy, instead of to actually do the copy. See http://php.net/manual/en/language.oop5.cloning.php

t5158846 for fixing the issue in Facebook.

[jwatzman]

Pretty sure we already do this for __construct (since we special case that enormously), but seems useful for the others too.

[lexidor]

Not needed for __destruct(), since it is gone. Adding it to __clone() would be a major improvement.

[lexidor]

Tracked as hhvm/hhast#546