The standard build environment 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 stdenv. 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.

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 ]; };

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 { 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.

Currently supported interpreters are python26, python27, python32, python33, python34 and pypy. python is an alias of python27 and python3 is an alias of python34. python26 and python27 do not include modules that require external dependencies (to reduce dependency bloat). Following modules need to be added as buildInput explicitly: python.modules.bsddb python.modules.curses python.modules.curses_panel python.modules.crypt python.modules.gdbm python.modules.sqlite3 python.modules.tkinter python.modules.readline For convenience python27Full and python26Full are provided with all modules included. Python packages that use setuptools or distutils, can be built using the buildPythonPackage function as documented below. All packages depending on any Python interpreter get appended $out/${python.libPrefix}/site-packages to $PYTHONPATH if such directory exists. libPrefix Name of the folder in ${python}/lib/ for corresponding interpreter. interpreter Alias for ${python}/bin/${executable}. buildEnv Function to build python interpreter environments with extra packages bundled together. See for usage and documentation. sitePackages Alias for lib/${libPrefix}/site-packages. executable Name of the interpreter executable, ie python3.4.

The function is implemented in pkgs/development/python-modules/generic/default.nix. Example usage: twisted = buildPythonPackage { name = "twisted-8.1.0"; src = pkgs.fetchurl { url = http://tmrc.mit.edu/mirror/twisted/Twisted/8.1/Twisted-8.1.0.tar.bz2; sha256 = "0q25zbr4xzknaghha72mq57kh53qw1bf8csgp63pm9sfi72qhirl"; }; propagatedBuildInputs = [ self.ZopeInterface ]; meta = { homepage = http://twistedmatrix.com/; description = "Twisted, an event-driven networking engine written in Python"; license = stdenv.lib.licenses.mit; }; }; Most of Python packages that use buildPythonPackage are defined in pkgs/top-level/python-packages.nix and generated for each python interpreter separately into attribute sets python26Packages, python27Packages, python32Packages, python33Packages, python34Packages and pypyPackages. buildPythonPackage mainly does four things: In the configurePhase, it patches setup.py to always include setuptools before distutils for monkeypatching machinery to take place. In the buildPhase, it calls ${python.interpreter} setup.py build ... In the installPhase, it calls ${python.interpreter} setup.py install ... In the postFixup phase, wrapPythonPrograms bash function is called to wrap all programs in $out/bin/* directory to include $PYTHONPATH and $PATH environment variables. By default doCheck = true is set and tests are run with ${python.interpreter} setup.py test command in checkPhase. propagatedBuildInputs packages are propagated to user environment. By default meta.platforms is set to the same value as the interpreter unless overriden otherwise. namePrefix Prepended text to ${name} parameter. Defaults to "python3.3-" for Python 3.3, etc. Set it to "" if you're packaging an application or a command line tool. disabled If true, package is not build for particular python interpreter version. Grep around pkgs/top-level/python-packages.nix for examples. setupPyInstallFlags List of flags passed to setup.py install command. setupPyBuildFlags List of flags passed to setup.py build command. pythonPath List of packages to be added into $PYTHONPATH. Packages in pythonPath are not propagated into user environment (contrary to propagatedBuildInputs). preShellHook Hook to execute commands before shellHook. postShellHook Hook to execute commands after shellHook. distutilsExtraCfg Extra lines passed to [easy_install] section of distutils.cfg (acts as global setup.cfg configuration).

Create Python environments using low-level pkgs.buildEnv function. Example default.nix: {}; python.buildEnv.override { extraLibs = [ pkgs.pythonPackages.pyramid ]; ignoreCollisions = true; }]]> Running nix-build will create /nix/store/cf1xhjwzmdki7fasgr4kz6di72ykicl5-python-2.7.8-env with wrapped binaries in bin/. extraLibs List of packages installed inside the environment. postBuild Shell command executed after the build of environment. ignoreCollisions Ignore file collisions inside the environment (default is false).

Packages inside nixpkgs are written by hand. However many tools exist in community to help save time. No tool is preferred at the moment. python2nix by Vladimir Kirillov pypi2nix by Rok Garbas pypi2nix by Jaka Hudoklin

To develop Python packages buildPythonPackage has additional logic inside shellPhase to run ${python.interpreter} setup.py develop for the package. shellPhase is executed only if setup.py exists. Given a default.nix: {}; buildPythonPackage { name = "myproject"; buildInputs = with pkgs.pythonPackages; [ pyramid ]; src = ./.; }]]> Running nix-shell with no arguments should give you the environment in which the package would be build with nix-build. Shortcut to setup environments with C headers/libraries and python packages: $ nix-shell -p pythonPackages.pyramid zlib libjpeg git There is a boolean value lib.inNixShell set to true if nix-shell is invoked.

How to solve circular dependencies? If you have packages A and B that depend on each other, when packaging B override package A not to depend on B as input (and also the other way around). install_data / data_files problems resulting into error: could not create '/nix/store/6l1bvljpy8gazlsw2aw9skwwp4pmvyxw-python-2.7.8/etc': Permission denied Known bug in setuptools install_data does not respect --prefix. Example of such package using the feature is pkgs/tools/X11/xpra/default.nix. As workaround install it as an extra preInstall step: ${python.interpreter} setup.py install_data --install-dir=$out --root=$out sed -i '/ = data_files/d' setup.py Rationale of non-existent global site-packages There is no need to have global site-packages in Nix. Each package has isolated dependency tree and installing any python package will only populate $PATH inside user environment. See to create self-contained interpreter with a set of packages.

Following rules are desired to be respected: Make sure package builds for all python interpreters. Use disabled argument to buildPythonPackage to set unsupported interpreters. If tests need to be disabled for a package, make sure you leave a comment about reasoning. Packages in pkgs/top-level/python-packages.nix are sorted quasi-alphabetically to avoid merge conflicts.

For example, to package yajl-ruby package, use gem-nix: $ nix-env -i gem-nix $ gem-nix --no-user-install --nix-file=pkgs/development/interpreters/ruby/generated.nix yajl-ruby $ nix-build -A rubyPackages.yajl-ruby

The function buildGoPackage builds standard Go packages. net = buildGoPackage rec { name = "go.net-${rev}"; goPackagePath = "code.google.com/p/go.net"; subPackages = [ "ipv4" "ipv6" ]; rev = "28ff664507e4"; src = fetchhg { inherit rev; url = "https://${goPackagePath}"; sha256 = "1lkz4c9pyz3yz2yz18hiycvlfhgy3jxp68bs7mv7bcfpaj729qav"; }; propagatedBuildInputs = [ goPackages.text ]; }; is an example expression using buildGoPackage, the following arguments are of special significance to the function: goPackagePath specifies the package's canonical Go import path. subPackages limits the builder from building child packages that have not been listed. If subPackages is not specified, all child packages will be built. In this example only code.google.com/p/go.net/ipv4 and code.google.com/p/go.net/ipv4 will be built. propagatedBuildInputs is where the dependencies of a Go library are listed. Only libraries should list propagatedBuildInputs. If a standalone program is being build instead, use buildInputs. If a library's tests require additional dependencies that are not propagated, they should be listed in buildInputs. Reusable Go libraries may be found in the goPackages set. You can test build a Go package as follows: $ nix-build -A goPackages.net You may use Go packages installed into the active Nix profiles by adding the following to your ~/.bashrc: for p in $NIX_PROFILES; do GOPATH="$p/share/go:$GOPATH" done To extract dependency information from a Go package in automated way use go2nix.

Ant-based Java packages are typically built from source as follows: stdenv.mkDerivation { name = "..."; src = fetchurl { ... }; buildInputs = [ jdk ant ]; buildPhase = "ant"; } Note that jdk is an alias for the OpenJDK. JAR files that are intended to be used by other packages should be installed in $out/share/java. The OpenJDK has a stdenv setup hook that adds any JARs in the share/java directories of the build inputs to the CLASSPATH environment variable. For instance, if the package libfoo installs a JAR named foo.jar in its share/java directory, and another package declares the attribute buildInputs = [ jdk libfoo ]; then CLASSPATH will be set to /nix/store/...-libfoo/share/java/foo.jar. Private JARs should be installed in a location like $out/share/package-name. If your Java package provides a program, you need to generate a wrapper script to run it using the OpenJRE. You can use makeWrapper for this: buildInputs = [ makeWrapper ]; installPhase = '' mkdir -p $out/bin makeWrapper ${jre}/bin/java $out/bin/foo \ --add-flags "-cp $out/share/java/foo.jar org.foo.Main" ''; Note the use of jre, which is the part of the OpenJDK package that contains the Java Runtime Environment. By using ${jre}/bin/java instead of ${jdk}/bin/java, you prevent your package from depending on the JDK at runtime. It is possible to use a different Java compiler than javac from the OpenJDK. For instance, to use the Eclipse Java Compiler: buildInputs = [ jre ant ecj ]; (Note that here you don’t need the full JDK as an input, but just the JRE.) The ECJ has a stdenv setup hook that sets some environment variables to cause Ant to use ECJ, but this doesn’t work with all Ant files. Similarly, you can use the GNU Java Compiler: buildInputs = [ gcj ant ]; Here, Ant will automatically use gij (the GNU Java Runtime) instead of the OpenJRE.

Lua packages are built by the buildLuaPackage function. This function is implemented in pkgs/development/lua-modules/generic/default.nix and works similarly to buildPerlPackage. (See for details.) Lua packages are defined in pkgs/top-level/lua-packages.nix. Most of them are simple. For example: fileSystem = buildLuaPackage { name = "filesystem-1.6.2"; src = fetchurl { url = "https://github.com/keplerproject/luafilesystem/archive/v1_6_2.tar.gz"; sha256 = "1n8qdwa20ypbrny99vhkmx8q04zd2jjycdb5196xdhgvqzk10abz"; }; meta = { homepage = "https://github.com/keplerproject/luafilesystem"; hydraPlatforms = stdenv.lib.platforms.linux; maintainers = with maintainers; [ flosse ]; }; }; Though, more complicated package should be placed in a seperate file in pkgs/development/lua-modules. Lua packages accept additional parameter disabled, which defines the condition of disabling package from luaPackages. For example, if package has disabled assigned to lua.luaversion != "5.1", it will not be included in any luaPackages except lua51Packages, making it only be built for lua 5.1.

Coq libraries should be installed in $(out)/lib/coq/${coq.coq-version}/user-contrib/. Such directories are automatically added to the $COQPATH environment variable by the hook defined in the Coq derivation. Some libraries require OCaml and sometimes also Camlp5. The exact versions that were used to build Coq are saved in the coq.ocaml and coq.camlp5 attributes. Here is a simple package example. It is a pure Coq library, thus it only depends on Coq. Its makefile has been generated using coq_makefile so we only have to set the $COQLIB variable at install time. {stdenv, fetchurl, coq}: stdenv.mkDerivation { src = fetchurl { url = http://coq.inria.fr/pylons/contribs/files/Karatsuba/v8.4/Karatsuba.tar.gz; sha256 = "0ymfpv4v49k4fm63nq6gcl1hbnnxrvjjp7yzc4973n49b853c5b1"; }; name = "coq-karatsuba"; buildInputs = [ coq ]; installFlags = "COQLIB=$(out)/lib/coq/${coq.coq-version}/"; }