How to know if a CPAN module uses XS

bcarroll has asked for the wisdom of the Perl Monks concerning the following question:

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Re: How to know if a CPAN module uses XS by syphilis (Archbishop) on Jun 20, 2012 at 00:09 UTC
I just scan the MANIFEST (in the source distro) for a '.xs' file. Presence of one means that compiling is reqired; absence means no compilation is required. However, whilst this is a fairly reliable method, it's not foolproof. For example, PDL::NetCDF has no xs file yet requires compilation. (The 'perl Makefile.PL' step generates the xs file.) And I think there are some modules that, while providing an xs file, also cater for a pure-perl build. Perhaps some of the other monks know of a smarter approach. Cheers, Rob	[reply]
Re^2: How to know if a CPAN module uses XS by tobyink (Canon) on Jun 20, 2012 at 06:54 UTC
Another heuristic is to look for `use DynaLoader` or `use XSLoader` in any of the modules. XS code also often comes with a file called `typemap` which is used by the XS build system to map between Perl data structures and C data structures. And `ppport.h` is often bundled. This is a C header file which, as I understand it, smooths over the differences between versions of the Perl API. `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re^2: How to know if a CPAN module uses XS by etj (Deacon) on May 23, 2022 at 20:18 UTC
(The 'perl Makefile.PL' step generates the xs file.) It does not. The Makefile thereby generated has a rule that turns the supplied `.pd` file into `.pm` and `.xs` files, and for distributions that have "opted in" and with a PDL 2.058+, a `.c` file per operation (allowing parallel builds). Probably the best heuristic to spot a PDL distro that generates XS rather than being a pure-Perl user of other PDL modules is the use of PDL::Core::Dev, and/or calls to `pdlpp_stdargs`.	[reply] [d/l] [select]
Re: How to know if a CPAN module uses XS by toolic (Bishop) on Jun 20, 2012 at 00:35 UTC
A Super Search yielded the somewhat related Modules in CPAN that don't need to be compiled, but it does not give any more helpful advice than syphilis'. http://search.cpan.org uses DLSIP notation. The "L" indicates whether compile is needed. However, it requires CPAN authors to "Register" a newly uploaded module, which is voluntary, and in my experience, unreliable. IIRC, the DSLIP designation is manually entered by the author, which means it is subject to typos.	[reply]
Re^2: How to know if a CPAN module uses XS by mje (Curate) on Jun 20, 2012 at 10:27 UTC
Out of interest how can you see that module metadata? I know where you change it on pause but I can only see metadata for modules I own. There are some modules I maintain but I'm not the owner and I'd like to check them.	[reply]
Re^3: How to know if a CPAN module uses XS by Anonymous Monk on Jun 20, 2012 at 10:55 UTC
I can only see metadata for modules I own. That seems key :) CGI -> http://search.cpan.org/dist/CGI -> http://search.cpan.org/~markstos/ -> BACKUP -> HISTORY -> http://search.cpan.org/~lds/ -> BINGO -> CGI RpdOp https://metacpan.org/ doesn't bother with DLSIP at all, (speculating) probably because it can't gain access to that info , not that its used very often	[reply]
Re^2: How to know if a CPAN module uses XS by Anonymous Monk on Jun 20, 2012 at 02:08 UTC
DSLIP designation is manually entered by the author, which means it is subject to typos. AFAIK (its been 10 years) its a checkbox and/or dropdown menu list with descriptions, so typos not possible :)	[reply]
Re^3: How to know if a CPAN module uses XS by toolic (Bishop) on Jun 20, 2012 at 11:45 UTC
While not as easy to type in incorrect information, it is still possible to check the wrong box (I do it probably once a week here at the Monastery as I'm voting) or select the wrong dropdown item, without noticing. The point is that it is voluntary information which means it is error-prone.	[reply]
Re^4: How to know if a CPAN module uses XS by Anonymous Monk on Jun 20, 2012 at 12:01 UTC
Re: How to know if a CPAN module uses XS by bulk88 (Priest) on Jun 20, 2012 at 01:44 UTC
WriteMakefile returns a MM object which has has_link_code and needs_linking. Somehow calling these are your safest bet. If I had to try and do it, I would copy EUMM's WriteMakefile into my script, switch packages, define a new WriteMakefile based off EUMM's but without the flush() at the end, switch packages back to main, , run the makefile.pl with a do(), intercept the returning MM obj in my WriteMakefile, and call needs_linking(). The most complex use of EUMM I've ever seen was in Perl TK, and I did something similar to what I described to you to intercept Tk::MMutil::TkExtMakefile. Note this is not a "static" way of determining whether it needs to be compile, so security issues might be a problem for you. Another solution would be to generate the makefile, then do backticks on your make tool running in "list commands and do not execute" mode, then parse that looking for your local C compiler.	[reply]
Re^2: How to know if a CPAN module uses XS by syphilis (Archbishop) on Jun 20, 2012 at 09:14 UTC
I think the first difficulty (not necessarily a show-stopper) I see with that approach is that it relies on WriteMakefile() being run. However, some Makefile.PL's may abort prior to that happening - eg because $] is too low, or because $^O is inappropriate, or because some pre-requisite could not be found. Handle that, and you're probably on a winner. It may even be that if $] is too low or $^O is inappropriate, then you don't even need to know whether the module needs to be compiled ... and if the Makefile.PL aborts because a pre-requisite C library can't be found, then it should be safe to assume it's a module that needs compiling. But if the Makefile.PL aborts because a pre-requisite perl module could not be found, then all bets are off. (I've a notion that there are some modules that do that, though I can't provide an example.) then do backticks on your make tool running in "list commands and do not execute" mode And then there's Inline/Inline::C ... run make in "list commands and do not execute" mode when building Inline/Inline::C and you'll see no mention of any compiler. (But perhaps that's the right result anyway ... not sure about that one.) And, of course, not every distro has a Makefile.PL - and there's presumably a need to handle them, too. (That's the beauty of having a choice of 2 build systems - instead of solving a problem once, you get the added joy of having to solve it twice :-) Cheers, Rob	[reply]
Re^3: How to know if a CPAN module uses XS by bulk88 (Priest) on Jun 20, 2012 at 10:59 UTC
Hooking WriteMakefile wouldn't work on Module::Build, and it wouldn't work for a makefile.pl that gets $Config{cc} and runs the compiler itself. As said elsewhere in this thread, searching the source code for Dynaloader is another choice, even for this post Pure Perl module(246 lines, Linux/Win32) that calls external libraries - no XS file.. Then again "Dynaloader" as a string can be obfuscated.	[reply]


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