However, as functionality it could be provided as an extension first for a
proof of concept. The ingredients are all there, it doesn't need to be in
core:
1. Register an internal attribute, see my #[Deprecated] PR as an example
https://github.com/php/php-src/pull/6521
2. Register a zend_observer as a first step, that detects functions/methods
with a new #[Intercept] or whatever attribute you want and registers
observer callbacks. See ext/zend_test
https://github.com/php/php-src/blob/master/ext/zend_test/test.c or
tideways/php-xhprof-extension:
https://github.com/tideways/php-xhprof-extension/blob/master/tideways_xhprof.c#L30-L57
3. Use C API zend_call_function in the observer to call your interceptor.
Cobbling this together as a Frankestein monster from existing code should
be achievable even if you haven't worked with PHP core yet imho. This could
replace the php-aop extension that isn't maintained anymore.
Using a zend_obserer would only allow you to register a before and after
hook, the alternative with a "$wrapped()" would be significantly more
complex with the existing building blocks.
Hooking into zend_exeute_ex would allow you to implement around handling,
but at this point is not recommended anymore, because its incompatible with
JIT and might be removed in the future.