Improved reliability with Alien and Test::Alien

With the gracious collaboration with Cosimo,Text::Hunspell made the switch from ExtUtils::PkgConfig to Alien::Hunspell late late year. Despite the somewhat complicated dependency requirements, this immediately made the spell checker more reliable as reported by cpantesters, as many machines do not have pkg-config or hunspell installed.

The one major platform that didn’t work on the initial switch was of course Strawberry Perl, but after some debugging and patches I got Alien::Hunspell and Text::Hunspell to work there as well. I even submitted patches to upstream to the hunspell project, which were accepted, so that in the future less patching will be required. This is what is great about Open Source when it works.

The results as recorded in the cpantesters matrix are stark:

In the process of working on all of this I finally gave up on Test::CChecker. I wrote this module to test Alien distributions, and leveraged some capabilities from ExtUtils::CChecker, which is designed to probe and check compiler and linker flags from a Makefile.PL or Build.PL file.

Test::CChecker was a huge improvement over existing state of affairs for testing Aliens when I wrote it. For most such modules, this consisted of the hand rolled .t files that used the Config module and attempted to build executables by invoking the compiler via system or qx. Assuming that an Alien module even had any tests. Here is a simplified version of the Test::CChecker test that I wrote for Alien::Hunspell.

use Test::More;
use Alien::Hunspell;
use Test::CChecker 0.07;

plan tests => 2;


compile_with_alien 'Alien::Hunspell';

my $source = do { local $/; <DATA> };

compile_ok $source, 'basic compile test';

compile_run_ok $source, "basic compile/link/run test";

#include <hunspell.h>

main(int argc, char *argv[])
Hunhandle *h;

h = Hunspell_create("","");

return 0;

What this does is compile and link an executable using the flags provided by Alien::Hunspell. It then runs it and ensures that it doesn’t dump core, and returns a successful exit status. Simple(ish) for Alien right? The problem is that there are a number of subtle edge cases that become much more prominent when you are installing an Alien module that decides that it needs to build the upstream package from source. The biggest difference between what this test tests, and how the Alien module is actually used is that Text::Hunspell creates a dynamic library and links it to the running Perl process. This means that the test file catches errors specific to linking executables that aren’t pertinent to usage in Perl. It also means that this test file does NOT catch errors that are specific to dynamic libraries, which ARE pertinent to usage in Perl.

So I wrote Test::Alien to test Alien modules in the way that they are actually used. Create an interface to make it easy to create a mini-XS or FFI and run some basic tests like ensure you can query the version number. This increases the likelihood that the Alien module will actually be useful dramatically, and it catches errors with the Alien module where they should be found, in the Alien module itself, not in the downstream XS or FFI module. Here are simplified tests, also for Alien::Hunspell:

# test for XS
use Test::Stream -V1;
use Test::Alien;
use Alien::Hunspell;

plan 3;

alien_ok 'Alien::Hunspell';

my $xs = do { local $/; <DATA> };

xs_ok { xs => $xs, verbose => 1 }, with_subtest {
my $ptr = My::Hunspell::Hunspell_create("t/supp.aff","t/supp.dic");
ok $ptr, "ptr = $ptr";
ok 1, "did not crash";


#include "EXTERN.h"
#include "perl.h"
#include "XSUB.h"
#include <hunspell/hunspell.h>

MODULE = My::Hunspell PACKAGE = My::Hunspell

void *
Hunspell_create(affpath, dpath);
const char *affpath;
const char *dpath;

void *handle;

This tests that a basic dynamic extension can be built, and can create and destroy a simple hunspell instance without crashing.

# test for FFI
use Test::Stream -V1;
use Test::Alien;
use Alien::Hunspell;

plan 3;

alien_ok 'Alien::Hunspell';

ffi_ok { symbols => [qw( Hunspell_create Hunspell_destroy )] }, with_subtest {
my($ffi) = @_;

plan 2;

$ffi->attach(Hunspell_create => ['string','string'] => 'opaque');
my $ptr = Hunspell_create("t/supp.aff", "t/supp.dic");

ok $ptr, "ptr = $ptr";

$ffi->attach(Hunspell_destroy => ['opaque'] => 'void');

ok 1, "did not crash";

Test::Alien also has tests for tool oriented Alien modules, such as Alien::gmake and Alien::patch. Test::Alien is designed to work seamlessly with Alien::Base based Alien modules, but can also be made to work without much additional work with non Alien::Base based Aliens.

The other nice thing about the Test::Alien interface is that its tests will self skip if a compiler or FFI::Platypus are not found. This is useful, as Text::Hunspell::FFI can use Alien::Hunspell without a compiler if the hunspell system packages are installed, and conversely Text::Hunspell can use Alien::Hunspell if FFI::Platypus is not installed.

I used Test::Alien in development versions of Alien::Hunspell to identify and correct bugs to make it more reliable.


Thank you for all your hard work on Alien and FFI!

Interacting with C-alike libraries is becoming a much more friendlier business in Perl!

FYI, the recent issue of Pragmatic Perl features an article on using FFI::Platypus::Lang::Rust (beware, it is in Russian:)

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About Graham Ollis

user-pic Perl programmer with an interest in Alien and FFI technologies. Primary developer of FFI::Platypus and Alien::Build.