libclass-xsaccessor-perl: defining PERL_CORE for external XS modules and ABI stability

[Steffen Mueller]

Hi all,

Damyan Ivanov wrote:
> -=| Ansgar Burchardt, Mon, Aug 16, 2010 at 01:50:23PM +0900 |=-
>> Hi,
>>
>> the last upstream release of libclass-xsaccessor-perl (1.07) contains
>> this change:

Wow, you were quick to pick this up! The change in question is a 
(significant) optimization.

>> --- XSAccessor.xs       (revision 61639)
>> +++ XSAccessor.xs       (working copy)

[...]

>> + * defining PERL_CORE gets us the fast version, at the expense of a future maintenance release
>> + * possibly breaking things: http://www.xray.mpe.mpg.de/mailing-lists/perl5-porters/2008-04/msg00171.html

[...]

This is the important bit wrt. maintenance. It means that if I'm using 
any of the Perl internals, and they're changed in a future release, I 
get to keep all parts as a maintainer and get the wraith of the other 
perl5-porters as an extra benefit.

Effectively, we're not really making use of a lot of internals things. 
Additionally, since C::XSAccessor is fairly widely used and I track the 
core perl development, it's unlikely to be broken by a future *released* 
version of perl. Therefore, the worst case for you is that you'll have 
to repackage a future (fixed) version of Class::XSAccessor when you 
upgrade perl *and* that particular version of perl broke 
Class::XSAccessor 1.07.

>> I wonder whether it is safe to keep this in Debian as the XS modules depend
>> on perlapi-*, or if this does not guarantee that (internal) offsets do
>> not change and we should not define PERL_CORE for the Debian 
>> package.
> 
> I think keeping this is safe. Perhaps even defining PERL_CORE globally 
> would be safe. I guess the whle dance around perl internals is to 
> allow the XS module to work with a perl binary with a different ABI -- 
> something we solve differently in Debian.

I agree that it should be safe. Besides. I'm sure there's plenty of 
other CPAN modules packaged in debian that (similarly illegally) define 
PERL_CORE. I'd bet that quite a few modules even cargo-culted a "#define 
PERL_CORE" without needing it at all.

Cheers,
Steffen (one of the Class::XSAccessor guys)