This question is asked partially in frustration, but also partially in genuine curiosity.

What changes in recent #PHP versions have "required complete rewrites"? Really, which?

The most invasive changes I can think of in recent memory are "undefined vars are now E_WARNING" in 8.0, and "internal interfaces now have types" in 8.1. While addressing those can be annoying... they don't require a full redesign.

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