Description:
------------
Adding a class / interface constant that references to another constant via an array key that's non-existent kills the PHP process silently. (without invoking die() or exit())

There are no error messages thrown, nor a warning, or anything. PHP just dies.

There are two different results on two different scenarios.

If this bug was done on an interface, PHP silently kills itself, as mentioned for several times.

If this bug was done on a class, PHP Freezes silently and refuses to do anything. I've only tested this for a few minutes, I don't know if it un-freezes and exits after a while.

Due to no error messages are being displayed, this made debugging it a bit tricky at first. It took me quite a few minutes before finding out that it was an invalid array key access. Even while I'm using PHPStorm (the class constant 'ARRAY_1' is an empty array), the erroneous code does not get pointed out or highlighted.

Test script:
---------------
// Only use one of these to get different results.

// Insta-kill
interface BrokenInterface {
    // this can be anything... even null. just with a non-existent key
    public const ARRAY_1 = [];

    public const ARRAY_2 = [
        self::ARRAY_1["nonExistentKey"]
    ];
}
class UseThisClass implements BrokenInterface {}
(new UseThisClass());

// Freeze
class BrokenClass {
    // this can be anything... even null. just with a non-existent key
    public const ARRAY_1 = [];

    public const ARRAY_2 = [
        self::ARRAY_1["nonExistentKey"]
    ];
}
(new BrokenClass());

Expected result:
----------------
A Compile Error should be thrown.

Actual result:
--------------
PHP Silently shuts down without any warning or error message.