Perl
Nixpkgs provides a function buildPerlPackage, a generic
package builder function for any Perl package that has a standard
Makefile.PL. It’s implemented in
pkgs/development/perl-modules/generic.
Perl packages from CPAN are defined in
pkgs/top-level/perl-packages.nix,
rather than pkgs/all-packages.nix. Most Perl packages
are so straight-forward to build that they are defined here directly, rather
than having a separate function for each package called from
perl-packages.nix. However, more complicated packages
should be put in a separate file, typically in
pkgs/development/perl-modules. Here is an example of the
former:
ClassC3 = buildPerlPackage rec {
name = "Class-C3-0.21";
src = fetchurl {
url = "mirror://cpan/authors/id/F/FL/FLORA/${name}.tar.gz";
sha256 = "1bl8z095y4js66pwxnm7s853pi9czala4sqc743fdlnk27kq94gz";
};
};
Note the use of mirror://cpan/, and the
${name} in the URL definition to ensure that the name
attribute is consistent with the source that we’re actually downloading.
Perl packages are made available in all-packages.nix
through the variable perlPackages. For instance, if you
have a package that needs ClassC3, you would typically
write
foo = import ../path/to/foo.nix {
inherit stdenv fetchurl ...;
inherit (perlPackages) ClassC3;
};
in all-packages.nix. You can test building a Perl
package as follows:
$ nix-build -A perlPackages.ClassC3
buildPerlPackage adds perl- to the
start of the name attribute, so the package above is actually called
perl-Class-C3-0.21. So to install it, you can say:
$ nix-env -i perl-Class-C3
(Of course you can also install using the attribute name: nix-env -i
-A perlPackages.ClassC3.)
So what does buildPerlPackage do? It does the following:
In the configure phase, it calls perl Makefile.PL to
generate a Makefile. You can set the variable
makeMakerFlags to pass flags to
Makefile.PL
It adds the contents of the PERL5LIB environment variable
to #! .../bin/perl line of Perl scripts as
-Idir flags. This ensures
that a script can find its dependencies.
In the fixup phase, it writes the propagated build inputs
(propagatedBuildInputs) to the file
$out/nix-support/propagated-user-env-packages.
nix-env recursively installs all packages listed in
this file when you install a package that has it. This ensures that a Perl
package can find its dependencies.
buildPerlPackage is built on top of
stdenv, so everything can be customised in the usual way.
For instance, the BerkeleyDB module has a
preConfigure hook to generate a configuration file used by
Makefile.PL:
{ buildPerlPackage, fetchurl, db }:
buildPerlPackage rec {
name = "BerkeleyDB-0.36";
src = fetchurl {
url = "mirror://cpan/authors/id/P/PM/PMQS/${name}.tar.gz";
sha256 = "07xf50riarb60l1h6m2dqmql8q5dij619712fsgw7ach04d8g3z1";
};
preConfigure = ''
echo "LIB = ${db}/lib" > config.in
echo "INCLUDE = ${db}/include" >> config.in
'';
}
Dependencies on other Perl packages can be specified in the
buildInputs and propagatedBuildInputs
attributes. If something is exclusively a build-time dependency, use
buildInputs; if it’s (also) a runtime dependency, use
propagatedBuildInputs. For instance, this builds a Perl
module that has runtime dependencies on a bunch of other modules:
ClassC3Componentised = buildPerlPackage rec {
name = "Class-C3-Componentised-1.0004";
src = fetchurl {
url = "mirror://cpan/authors/id/A/AS/ASH/${name}.tar.gz";
sha256 = "0xql73jkcdbq4q9m0b0rnca6nrlvf5hyzy8is0crdk65bynvs8q1";
};
propagatedBuildInputs = [
ClassC3 ClassInspector TestException MROCompat
];
};
Generation from CPAN
Nix expressions for Perl packages can be generated (almost) automatically
from CPAN. This is done by the program
nix-generate-from-cpan, which can be installed as
follows:
$ nix-env -i nix-generate-from-cpan
This program takes a Perl module name, looks it up on CPAN, fetches and
unpacks the corresponding package, and prints a Nix expression on standard
output. For example:
$ nix-generate-from-cpan XML::Simple
XMLSimple = buildPerlPackage rec {
name = "XML-Simple-2.22";
src = fetchurl {
url = "mirror://cpan/authors/id/G/GR/GRANTM/${name}.tar.gz";
sha256 = "b9450ef22ea9644ae5d6ada086dc4300fa105be050a2030ebd4efd28c198eb49";
};
propagatedBuildInputs = [ XMLNamespaceSupport XMLSAX XMLSAXExpat ];
meta = {
description = "An API for simple XML files";
license = with stdenv.lib.licenses; [ artistic1 gpl1Plus ];
};
};
The output can be pasted into
pkgs/top-level/perl-packages.nix or wherever else you
need it.
Cross-compiling modules
Nixpkgs has experimental support for cross-compiling Perl modules. In many
cases, it will just work out of the box, even for modules with native
extensions. Sometimes, however, the Makefile.PL for a module may
(indirectly) import a native module. In that case, you will need to make a
stub for that module that will satisfy the Makefile.PL and install it into
lib/perl5/site_perl/cross_perl/${perl.version}. See the
postInstall for DBI for an example.