Custom Build Systems¶
While the build systems listed above should meet your needs for the vast majority of packages, some packages provide custom build scripts. This guide is intended for the following use cases:
- Packaging software with its own custom build system
- Adding support for new build systems
If you want to add support for a new build system, a good place to start is to look at the definitions of other build systems. This guide focuses mostly on how Spack’s build systems work.
In this guide, we will be using the
packages as examples.
perl’s build system is a hand-written
Configure shell script, while
cmake bootstraps itself during
installation. Both of these packages require custom build systems.
If your package does not belong to any of the aforementioned build
systems that Spack already supports, you should inherit from the
Package base class.
Package is a simple base class with a
install. If your package is simple, you may be able
to simply write an
install method that gets the job done. However,
if your package is more complex and installation involves multiple
steps, you should add separate phases as mentioned in the next section.
If you are creating a new build system base class, you should inherit
PackageBase. This is the superclass for all build systems in
The most important concept in Spack’s build system support is the idea of phases. Each build system defines a set of phases that are necessary to install the package. They usually follow some sort of “configure”, “build”, “install” guideline, but any of those phases may be missing or combined with another phase.
If you look at the
perl package, you’ll see:
phases = ['configure', 'build', 'install']
phases = ['bootstrap', 'build', 'install']
If we look at the
cmake example, this tells Spack’s
class to run the
in that order. It is now up to you to define these methods.
Phase and phase_args functions¶
If we look at
perl, we see that it defines a
def configure(self, spec, prefix): configure = Executable('./Configure') configure(*self.configure_args())
There is also a corresponding
configure_args function that handles
all of the arguments to pass to
Configure, just like in
AutotoolsPackage. Comparatively, the
phases are pretty simple:
def build(self, spec, prefix): make() def install(self, spec, prefix): make('install')
cmake package looks very similar, but with a
function instead of
def bootstrap(self, spec, prefix): bootstrap = Executable('./bootstrap') bootstrap(*self.bootstrap_args()) def build(self, spec, prefix): make() def install(self, spec, prefix): make('install')
Again, there is a
boostrap_args function that determines the
correct bootstrap flags to use.
Occasionally, you may want to run extra steps either before or after
a given phase. This applies not just to custom build systems, but to
existing build systems as well. You may need to patch a file that is
generated by configure, or install extra files in addition to what
make install copies to the installation prefix. This is where
@run_after come in.
These Python decorators allow you to write functions that are called
before or after a particular phase. For example, in
perl, we see:
@run_after('install') def install_cpanm(self): spec = self.spec if '+cpanm' in spec: with working_dir(join_path('cpanm', 'cpanm')): perl = spec['perl'].command perl('Makefile.PL') make() make('install')
This extra step automatically installs
cpanm in addition to the
base Perl installation.
run_after logic discussed above becomes
particularly powerful when combined with the
decorator. This decorator allows you to conditionally run certain
functions depending on the attributes of that package. The most
common example is conditional testing. Many unit tests are prone to
failure, even when there is nothing wrong with the installation.
Unfortunately, non-portable unit tests and tests that are
“supposed to fail” are more common than we would like. Instead of
always running unit tests on installation, Spack lets users
conditionally run tests with the
If we wanted to define a function that would conditionally run if and only if this flag is set, we would use the following line:
Let’s put everything together and add unit tests to our package.
perl package, we can see:
@run_after('build') @on_package_attributes(run_tests=True) def test(self): make('test')
As you can guess, this runs
make test after building the package,
if and only if testing is requested. Again, this is not specific to
custom build systems, it can be added to existing build systems as well.
Ideally, every package in Spack will have some sort of test to ensure
that it was built correctly. It is up to the package authors to make
sure this happens. If you are adding a package for some software and
the developers list commands to test the installation, please add these
tests to your
The order of decorators matters. The following ordering:
works as expected. However, if you reverse the ordering:
the tests will always be run regardless of whether or not
--test=root is requested. See https://github.com/spack/spack/issues/3833
for more information