PerlNixpkgs 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.PLIt 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 CPANNix 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 {
name = "XML-Simple-2.20";
src = fetchurl {
url = mirror://cpan/authors/id/G/GR/GRANTM/XML-Simple-2.20.tar.gz;
sha256 = "5cff13d0802792da1eb45895ce1be461903d98ec97c9c953bc8406af7294434a";
};
propagatedBuildInputs = [ XMLNamespaceSupport XMLSAX XMLSAXExpat ];
meta = {
description = "Easily read/write XML (esp config files)";
license = "perl";
};
};
The output can be pasted into
pkgs/top-level/perl-packages.nix or wherever else
you need it.