<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="chap-language-support"> <title>Support for specific programming languages</title> <para>The <link linkend="chap-stdenv">standard build environment</link> makes it easy to build typical Autotools-based packages with very little code. Any other kind of package can be accomodated by overriding the appropriate phases of <literal>stdenv</literal>. However, there are specialised functions in Nixpkgs to easily build packages for other programming languages, such as Perl or Haskell. These are described in this chapter.</para> <section xml:id="ssec-language-perl"><title>Perl</title> <para>Nixpkgs provides a function <varname>buildPerlPackage</varname>, a generic package builder function for any Perl package that has a standard <varname>Makefile.PL</varname>. It’s implemented in <link xlink:href="https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/development/perl-modules/generic"><filename>pkgs/development/perl-modules/generic</filename></link>.</para> <para>Perl packages from CPAN are defined in <link xlink:href="https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/top-level/perl-packages.nix"><filename>pkgs/perl-packages.nix</filename></link>, rather than <filename>pkgs/all-packages.nix</filename>. 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 <filename>perl-packages.nix</filename>. However, more complicated packages should be put in a separate file, typically in <filename>pkgs/development/perl-modules</filename>. Here is an example of the former: <programlisting> ClassC3 = buildPerlPackage rec { name = "Class-C3-0.21"; src = fetchurl { url = "mirror://cpan/authors/id/F/FL/FLORA/${name}.tar.gz"; sha256 = "1bl8z095y4js66pwxnm7s853pi9czala4sqc743fdlnk27kq94gz"; }; }; </programlisting> Note the use of <literal>mirror://cpan/</literal>, and the <literal>${name}</literal> 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 <filename>all-packages.nix</filename> through the variable <varname>perlPackages</varname>. For instance, if you have a package that needs <varname>ClassC3</varname>, you would typically write <programlisting> foo = import ../path/to/foo.nix { inherit stdenv fetchurl ...; inherit (perlPackages) ClassC3; }; </programlisting> in <filename>all-packages.nix</filename>. You can test building a Perl package as follows: <screen> $ nix-build -A perlPackages.ClassC3 </screen> <varname>buildPerlPackage</varname> adds <literal>perl-</literal> to the start of the name attribute, so the package above is actually called <literal>perl-Class-C3-0.21</literal>. So to install it, you can say: <screen> $ nix-env -i perl-Class-C3 </screen> (Of course you can also install using the attribute name: <literal>nix-env -i -A perlPackages.ClassC3</literal>.)</para> <para>So what does <varname>buildPerlPackage</varname> do? It does the following: <orderedlist> <listitem><para>In the configure phase, it calls <literal>perl Makefile.PL</literal> to generate a Makefile. You can set the variable <varname>makeMakerFlags</varname> to pass flags to <filename>Makefile.PL</filename></para></listitem> <listitem><para>It adds the contents of the <envar>PERL5LIB</envar> environment variable to <literal>#! .../bin/perl</literal> line of Perl scripts as <literal>-I<replaceable>dir</replaceable></literal> flags. This ensures that a script can find its dependencies.</para></listitem> <listitem><para>In the fixup phase, it writes the propagated build inputs (<varname>propagatedBuildInputs</varname>) to the file <filename>$out/nix-support/propagated-user-env-packages</filename>. <command>nix-env</command> recursively installs all packages listed in this file when you install a package that has it. This ensures that a Perl package can find its dependencies.</para></listitem> </orderedlist> </para> <para><varname>buildPerlPackage</varname> is built on top of <varname>stdenv</varname>, so everything can be customised in the usual way. For instance, the <literal>BerkeleyDB</literal> module has a <varname>preConfigure</varname> hook to generate a configuration file used by <filename>Makefile.PL</filename>: <programlisting> {buildPerlPackage, fetchurl, db4}: buildPerlPackage rec { name = "BerkeleyDB-0.36"; src = fetchurl { url = "mirror://cpan/authors/id/P/PM/PMQS/${name}.tar.gz"; sha256 = "07xf50riarb60l1h6m2dqmql8q5dij619712fsgw7ach04d8g3z1"; }; preConfigure = '' echo "LIB = ${db4}/lib" > config.in echo "INCLUDE = ${db4}/include" >> config.in ''; } </programlisting> </para> <para>Dependencies on other Perl packages can be specified in the <varname>buildInputs</varname> and <varname>propagatedBuildInputs</varname> attributes. If something is exclusively a build-time dependency, use <varname>buildInputs</varname>; if it’s (also) a runtime dependency, use <varname>propagatedBuildInputs</varname>. For instance, this builds a Perl module that has runtime dependencies on a bunch of other modules: <programlisting> ClassC3Componentised = buildPerlPackage rec { name = "Class-C3-Componentised-1.0004"; src = fetchurl { url = "mirror://cpan/authors/id/A/AS/ASH/${name}.tar.gz"; sha256 = "0xql73jkcdbq4q9m0b0rnca6nrlvf5hyzy8is0crdk65bynvs8q1"; }; propagatedBuildInputs = [ ClassC3 ClassInspector TestException MROCompat ]; }; </programlisting> </para> </section> <section><title>Python</title> <para> Python packages that use <link xlink:href="http://pypi.python.org/pypi/setuptools/"><literal>setuptools</literal></link>, which many Python packages do nowadays, can be built very simply using the <varname>buildPythonPackage</varname> function. This function is implemented in <link xlink:href="https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/development/python-modules/generic/default.nix"><filename>pkgs/development/python-modules/generic/default.nix</filename></link> and works similarly to <varname>buildPerlPackage</varname>. (See <xref linkend="ssec-language-perl"/> for details.) </para> <para> Python packages that use <varname>buildPythonPackage</varname> are defined in <link xlink:href="https://svn.nixos.org/repos/nix/nixpkgs/trunk/pkgs/top-level/python-packages.nix"><filename>pkgs/top-level/python-packages.nix</filename></link>. Most of them are simple. For example: <programlisting> twisted = buildPythonPackage { name = "twisted-8.1.0"; src = fetchurl { url = http://tmrc.mit.edu/mirror/twisted/Twisted/8.1/Twisted-8.1.0.tar.bz2; sha256 = "0q25zbr4xzknaghha72mq57kh53qw1bf8csgp63pm9sfi72qhirl"; }; propagatedBuildInputs = [ pkgs.ZopeInterface ]; meta = { homepage = http://twistedmatrix.com/; description = "Twisted, an event-driven networking engine written in Python"; license = "MIT"; }; }; </programlisting> </para> </section> <!-- <section><title>Haskell</title> <para>TODO</para> </section> <section><title>Java</title> <para>TODO; Java support needs lots of improvement</para> </section> <section><title>TeX / LaTeX</title> <para>* Special support for building TeX documents</para> </section> --> </chapter>