Magic-v2, Clone, and a possible `sv_clone` API function

I've been looking around CPAN for possible modules that might break
with some of the new "Magic v2" things I am lining up for next
development cycle. Originally I was looking for things that might get
upset if we start removing any of the internal v1 magic types, and I
encountered the Clone module - because it has a comment mentioning
PERL_MAGIC_arylen. While this itself is just a comment, on a further
reading of the code in that module it looks like it's actually
concerned quite closely with a lot of the details of how Magic (v1)
currently works. This code wouldn't cope well with v2 Magic structures.

My first thought for thinking about Magic-v2 is that a lot of the code
would need quite a bit of editing and adjusting.

Looking around CPAN more I also see that the code has basically been
copy-pasted into at least two other dists; Clone-AsUTF8Bytes and
Class-XSConstructor. This starts to suggest that actually, rather than
living in a CPAN module, this sort of "sv_clone" API function ought to
exist at the core perl level itself. That way, it would be able to do
the right thing with a new version of Magic, or any other newer
behaviours that get added.

(While I'm there I notice it also doesn't handle SVt_PVOBJ, the new
"object" SV type that was added in Perl 5.38 as part of the `class`
feature, so that too would want to be looked at).

Perhaps between us we can manage to find a good solution here.

-- 
Paul "LeoNerd" Evans

[email protected]
http://www.leonerd.org.uk/  |  https://metacpan.org/author/PEVANS