Description:
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Easy reproducible segmentation fault.
It seems that count($this) doesn't check recursion. I think that count($this) should check if it is called inside of $this->count(), and if so, should ignore the Countable interface and just count the properties. Use case: if your object got special properties that you do not want to count, you can use something liek that: "function count() {return count($this) - numberOfSpecialProperties;}" 

Test script:
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class A implements Countable {function count() {return count($this);}} count(new A);

Expected result:
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0

Actual result:
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Segmentation fault.