Package Creation Tutorial

This tutorial will walk you through the steps behind building a simple package installation script. We’ll focus building an mpileaks package, which is a MPI debugging tool. By creating a package file we’re essentially giving Spack a recipe for how to build a particular piece of software. We’re describing some of the software’s dependencies, where to find the package, what commands and options are used to build the package from source, and more. Once we’ve specified a package’s recipe, we can ask Spack to build that package in many different ways.

This tutorial assumes you have a basic familiarity with some of the Spack commands, and that you have a working version of Spack installed. If not, we suggest looking at Spack’s Getting Started guide. This tutorial also assumes you have at least a beginner’s-level familiarity with Python.

Also note that this document is a tutorial. It can help you get started with packaging, but is not intended to be complete. See Spack’s Packaging Guide for more complete documentation on this topic.

Getting Started

A few things before we get started:

  • We’ll refer to the Spack installation location via the environment variable SPACK_ROOT. You should point SPACK_ROOT at wherever you have Spack installed.
  • Add $SPACK_ROOT/bin to your PATH before you start.
  • Make sure your EDITOR environment variable is set to some text editor you like.
  • We’ll be writing Python code as part of this tutorial. You can find successive versions of the Python code in $SPACK_ROOT/lib/spack/docs/tutorial/examples.

Creating the Package File

Spack comes with a handy command to create a new package: spack create

This command is given the location of a package’s source code, downloads the code, and sets up some basic packaging infrastructure for you. The mpileaks source code can be found on GitHub, and here’s what happens when we run spack create on it:

$ spack create -f https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz
==> This looks like a URL for mpileaks version 1.0
==> Creating template for package mpileaks
==> Downloading...
==> Fetching https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz
###################################################################################### 100.0%

And Spack should spawn a text editor with this file:

##############################################################################
# Copyright (c) 2013-2016, Lawrence Livermore National Security, LLC.
# Produced at the Lawrence Livermore National Laboratory.
#
# This file is part of Spack.
# Created by Todd Gamblin, tgamblin@llnl.gov, All rights reserved.
# LLNL-CODE-647188
#
# For details, see https://github.com/llnl/spack
# Please also see the LICENSE file for our notice and the LGPL.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License (as
# published by the Free Software Foundation) version 2.1, February 1999.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the terms and
# conditions of the GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public
# License along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
##############################################################################
#
# This is a template package file for Spack.  We've put "FIXME"
# next to all the things you'll want to change. Once you've handled
# them, you can save this file and test your package like this:
#
#     spack install mpileaks
#
# You can edit this file again by typing:
#
#     spack edit mpileaks
#
# See the Spack documentation for more information on packaging.
# If you submit this package back to Spack as a pull request,
# please first remove this boilerplate and all FIXME comments.
#
from spack import *


class Mpileaks(AutotoolsPackage):
    """FIXME: Put a proper description of your package here."""

    # FIXME: Add a proper url for your package's homepage here.
    homepage = "http://www.example.com"
    url      = "https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz"

    version('1.0', '8838c574b39202a57d7c2d68692718aa')

    # FIXME: Add dependencies if required.
    # depends_on('m4', type='build')
    # depends_on('autoconf', type='build')
    # depends_on('automake', type='build')
    # depends_on('libtool', type='build')
    # depends_on('foo')

    def configure_args(self):
        # FIXME: Add arguments other than --prefix
        # FIXME: If not needed delete the function
        args = []
        return args

Spack has created this file in $SPACK_ROOT/var/spack/repos/builtin/packages/mpileaks/package.py. Take a moment to look over the file. There’s a few placeholders that Spack has created, which we’ll fill in as part of this tutorial:

  • We’ll document some information about this package in the comments.
  • We’ll fill in the dependency list for this package.
  • We’ll fill in some of the configuration arguments needed to build this package.

For the moment, exit your editor and let’s see what happens when we try to build this package:

$ spack install mpileaks
==> Installing mpileaks
==> Using cached archive: /usr/workspace/wsa/legendre/spack/var/spack/cache/mpileaks/mpileaks-1.0.tar.gz
==> Staging archive: /usr/workspace/wsa/legendre/spack/var/spack/stage/mpileaks-1.0-hufwhwpq5benv3sslie6ryflk5s6nm35/mpileaks-1.0.tar.gz
==> Created stage in /usr/workspace/wsa/legendre/spack/var/spack/stage/mpileaks-1.0-hufwhwpq5benv3sslie6ryflk5s6nm35
==> Ran patch() for mpileaks
==> Building mpileaks [AutotoolsPackage]
==> Executing phase : 'autoreconf'
==> Executing phase : 'configure'
==> Error: ProcessError: Command exited with status 1:
    './configure' '--prefix=/usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/mpileaks-1.0-hufwhwpq5benv3sslie6ryflk5s6nm35'
/usr/workspace/wsa/legendre/spack/lib/spack/spack/build_systems/autotools.py:150, in configure:
     145      def configure(self, spec, prefix):
     146          """Runs configure with the arguments specified in `configure_args`
     147          and an appropriately set prefix
     148          """
     149          options = ['--prefix={0}'.format(prefix)] + self.configure_args()
  >> 150          inspect.getmodule(self).configure(*options)

See build log for details:
  /tmp/legendre/spack-stage/spack-stage-8HVzqu/mpileaks-1.0/spack-build.out

This obviously didn’t work; we need to fill in the package-specific information. Specifically, Spack didn’t try to build any of mpileaks’ dependencies, nor did it use the proper configure arguments. Let’s start fixing things

Package Documentation

We can bring the package.py file back into our EDITOR with the spack edit command:

$ spack edit mpileaks

Let’s remove some of the FIXME comments, and add links to the mpileaks homepage and document what mpileaks does. I’m also going to cut out the Copyright clause at this point to keep this tutorial document shorter, but you shouldn’t do that normally. The results of these changes can be found in $SPACK_ROOT/lib/spack/docs/tutorial/examples/1.package.py and are below. Make these changes to your package.py:

from spack import *


class Mpileaks(AutotoolsPackage):
    """Tool to detect and report MPI objects like MPI_Requests and
    MPI_Datatypes."""

    homepage = "https://github.com/hpc/mpileaks"
    url      = "https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz"

    version('1.0', '8838c574b39202a57d7c2d68692718aa')

    # FIXME: Add dependencies if required.
    # depends_on('m4', type='build')
    # depends_on('autoconf', type='build')
    # depends_on('automake', type='build')
    # depends_on('libtool', type='build')
    # depends_on('foo')

    def configure_args(self):
        # FIXME: Add arguments other than --prefix
        # FIXME: If not needed delete the function
        args = []
        return args

We’ve filled in the comment that describes what this package does and added a link to the web site. That won’t help us build yet, but it will allow Spack to provide some documentation on this package to other users:

$ spack info mpileaks
AutotoolsPackage:    mpileaks
Homepage:            https://github.com/hpc/mpileaks

Safe versions:
    1.0    https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz

Variants:
    None

Installation Phases:
    autoreconf    configure    build    install

Build Dependencies:
    None

Link Dependencies:
    None

Run Dependencies:
    None

Virtual Packages:
    None

Description:
    Tool to detect and report MPI objects like MPI_Requests and
    MPI_Datatypes

As we fill in more information about this package the spack info command will become more informative. Now let’s start making this package build.

Dependencies

The mpileaks packages depends on three other package: MPI, adept-utils, and callpath. Let’s add those via the depends_on command in our package.py (this version is in $SPACK_ROOT/lib/spack/docs/tutorial/examples/2.package.py):

from spack import *


class Mpileaks(AutotoolsPackage):
    """Tool to detect and report MPI objects like MPI_Requests and
    MPI_Datatypes."""

    homepage = "https://github.com/hpc/mpileaks"
    url      = "https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz"

    version('1.0', '8838c574b39202a57d7c2d68692718aa')

    depends_on('mpi')
    depends_on('adept-utils')
    depends_on('callpath')

    def configure_args(self):
        # FIXME: Add arguments other than --prefix
        # FIXME: If not needed delete the function
        args = []
        return args

Now when we go to build mpileaks, Spack will fetch and build these dependencies before building mpileaks. Note that the mpi dependency is a different kind of beast than the adept-utils and callpath dependencies; there is no mpi package available in Spack. Instead mpi is a virtual dependency. Spack may satisfy that dependency by installing packages such as openmpi or mvapich. See the Packaging Guide for more information on virtual dependencies.

Now when we try to install this package a lot more happens:

$ spack install mpileaks
==> Installing mpileaks
==> openmpi is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz
==> callpath is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/callpath-1.0.2-zm4pf3gasgxeibyu2y262suktvaazube
==> adept-utils is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/adept-utils-1.0.1-7p7ezxwtajdglj6cmojy2vybjct4j4jz
==> Using cached archive: /usr/workspace/wsa/legendre/spack/var/spack/cache/mpileaks/mpileaks-1.0.tar.gz
==> Already staged mpileaks-1.0-eum4hmnlt6ovalwjnciaygfb3beja4gk in /usr/workspace/wsa/legendre/spack/var/spack/stage/mpileaks-1.0-eum4hmnlt6ovalwjnciaygfb3beja4gk
==> Already patched mpileaks
==> Building mpileaks [AutotoolsPackage]
==> Executing phase : 'autoreconf'
==> Executing phase : 'configure'
==> Error: ProcessError: Command exited with status 1:
    './configure' '--prefix=/usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/mpileaks-1.0-eum4hmnlt6ovalwjnciaygfb3beja4gk'
/usr/workspace/wsa/legendre/spack/lib/spack/spack/build_systems/autotools.py:150, in configure:
     145      def configure(self, spec, prefix):
     146          """Runs configure with the arguments specified in `configure_args`
     147          and an appropriately set prefix
     148          """
     149          options = ['--prefix={0}'.format(prefix)] + self.configure_args()
  >> 150          inspect.getmodule(self).configure(*options)

See build log for details:
  /tmp/legendre/spack-stage/spack-stage-7V5yyk/mpileaks-1.0/spack-build.out

Note that this command may take a while to run and produce more output if you don’t have an MPI already installed or configured in Spack.

Now Spack has identified and made sure all of our dependencies have been built. It found the openmpi package that will satisfy our mpi dependency, and the callpath and adept-utils package to satisfy our concrete dependencies.

Debugging Package Builds

Our mpileaks package is still not building. It may be obvious to many of you that we’re still missing the configure options. But let’s pretend we’re not all intelligent developers and use this opportunity spend some time debugging. We a few options that can tell us about what’s going wrong:

As per the error message, Spack has given us a spack-build.out debug log:

==> './configure' '--prefix=/usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/mpileaks-1.0-eum4hmnlt6ovalwjnciaygfb3beja4gk'
checking metadata... no
checking installation directory variables... yes
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /usr/bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking for gcc... /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc accepts -g... yes
checking for /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc option to accept ISO C89... none needed
checking for style of include used by make... GNU
checking dependency style of /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc... gcc3
checking whether /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc and cc understand -c and -o together... yes
checking whether we are using the GNU C++ compiler... yes
checking whether /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/g++ accepts -g... yes
checking dependency style of /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/g++... gcc3
checking for /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz/bin/mpicc... /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz/bin/mpicc
Checking whether /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz/bin/mpicc responds to '-showme:compile'... yes
configure: error: unable to locate ``adept-utils`` installation

This gives us the output from the build, and it’s fairly obvious that mpileaks isn’t finding its adept-utils package. Spack has automatically added the include and library directories of adept-utils to the compiler’s search path, but some packages like mpileaks can sometimes be picky and still want things spelled out on their command line. But let’s continue to pretend we’re not brilliant developers, and explore some other debugging paths:

We can also enter the build area and try to manually run the build:

$ spack env mpileaks bash
$ spack cd mpileaks

The spack env command spawned a new shell that contains the same environment that Spack used to build the mpileaks package (you can substitute bash for your favorite shell). The spack cd command changed our working dirctory to the last attempted build for mpileaks. From here we can manually re-run the build:

$ ./configure
checking metadata... no
checking installation directory variables... yes
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /usr/bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking for gcc... /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables...
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc accepts -g... yes
checking for /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc option to accept ISO C89... none needed
checking for style of include used by make... GNU
checking dependency style of /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc... gcc3
checking whether /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/gcc and cc understand -c and -o together... yes
checking whether we are using the GNU C++ compiler... yes
checking whether /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/g++ accepts -g... yes
checking dependency style of /usr/workspace/wsa/legendre/spack/lib/spack/env/gcc/g++... gcc3
checking for /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz/bin/mpicc... /usr/workspace/wsa  /legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz/bin/mpicc
Checking whether /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz/bin/mpicc responds to '-showme:compile'... yes
configure: error: unable to locate adept-utils installation

We’re seeing the same error, but now we’re in a shell where we can run the command ourselves and debug as needed. We could, for example, run ./configure --help to see what options we can use to specify dependencies.

We can use the exit command to leave the shell spawned by spack env.

Specifying Configure Arguments

Let’s add the configure arguments to the mpileaks’ package.py. This version can be found in $SPACK_ROOT/lib/spack/docs/tutorial/examples/3.package.py:

from spack import *


class Mpileaks(AutotoolsPackage):
    """Tool to detect and report MPI objects like MPI_Requests and
    MPI_Datatypes."""
    homepage = "https://github.com/hpc/mpileaks"
    url      = "https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz"

    version('1.0', '8838c574b39202a57d7c2d68692718aa')

    depends_on('mpi')
    depends_on('adept-utils')
    depends_on('callpath')

    def configure_args(self):
        args = ['--with-adept-utils=%s' % self.spec['adept-utils'].prefix,
                '--with-callpath=%s' % self.spec['callpath'].prefix]
        return args

This is all we need for working mpileaks! If we install now we’ll see:

$ spack install mpileaks
spack install mpileaks
==> Installing mpileaks
==> openmpi is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz
==> callpath is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/callpath-1.0.2-zm4pf3gasgxeibyu2y262suktvaazube
==> adept-utils is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/adept-utils-1.0.1-7p7ezxwtajdglj6cmojy2vybjct4j4jz
==> Using cached archive: /usr/workspace/wsa/legendre/spack/var/spack/cache/mpileaks/mpileaks-1.0.tar.gz
==> Already staged mpileaks-1.0-eum4hmnlt6ovalwjnciaygfb3beja4gk in /usr/workspace/wsa/legendre/spack/var/spack/stage/mpileaks-1.0-eum4hmnlt6ovalwjnciaygfb3beja4gk
==> Already patched mpileaks
==> Building mpileaks [AutotoolsPackage]
==> Executing phase : 'autoreconf'
==> Executing phase : 'configure'
==> Executing phase : 'build'
==> Executing phase : 'install'
==> Successfully installed mpileaks
  Fetch: 0.00s.  Build: 14.08s.  Total: 14.08s.
[+] /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/mpileaks-1.0-eum4hmnlt6ovalwjnciaygfb3beja4gk

We took a few shortcuts for this package that are worth highlighting. Spack automatically detected that mpileaks was an Autotools-based package when we ran spack create. If this had been a CMake-based package we would have been filling in a cmake_args function instead of configure_args. If Spack hadn’t been able to detect the build system, we’d be filling in a generic install method that would manually be calling build commands, such as is found in the zlib package:

def install(self, spec, prefix):
    configure('--prefix={0}'.format(prefix))
    make()
    make('install')

Variants

We have a successful mpileaks build, but let’s take some time to improve it. mpileaks has a build-time option to truncate parts of the stack that it walks. Let’s add a variant to allow users to set this when they build in Spack.

To do this, we’ll add a variant to our package, as per the following (see $SPACK_ROOT/lib/spack/docs/tutorial/examples/4.package.py):

from spack import *


class Mpileaks(AutotoolsPackage):
    """Tool to detect and report MPI objects like MPI_Requests and
    MPI_Datatypes."""

    homepage = "https://github.com/hpc/mpileaks"
    url      = "https://github.com/hpc/mpileaks/releases/download/v1.0/mpileaks-1.0.tar.gz"

    version('1.0', '8838c574b39202a57d7c2d68692718aa')

    variant('stackstart', default=0, description='Specify the number of stack frames to truncate.')

    depends_on('mpi')
    depends_on('adept-utils')
    depends_on('callpath')

    def configure_args(self):
        args = ['--with-adept-utils=%s' % self.spec['adept-utils'].prefix,
                '--with-callpath=%s' % self.spec['callpath'].prefix]
        stackstart = int(self.spec.variants['stackstart'].value)
        if stackstart:
            args.extend(['--with-stack-start-c=%s' % stackstart,
                         '--with-stack-start-fortran=%s' % stackstart])
        return args

We’ve added the variant stackstart, and given it a default value of 0. If we install now we can see the stackstart variant added to the configure line (output truncated for length):

$ spack install --verbose mpileaks stackstart=4
==> Installing mpileaks
==> openmpi is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/openmpi-2.0.1-5ee5j34c2y4kb5c3joygrgahidqnwhnz
==> callpath is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/callpath-1.0.2-zm4pf3gasgxeibyu2y262suktvaazube
==> adept-utils is already installed in /usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/adept-utils-1.0.1-7p7ezxwtajdglj6cmojy2vybjct4j4jz
==> Using cached archive: /usr/workspace/wsa/legendre/spack/var/spack/cache/mpileaks/mpileaks-1.0.tar.gz
==> Staging archive: /usr/workspace/wsa/legendre/spack/var/spack/stage/mpileaks-1.0-otqo2opkhan5ksujt6tpmdftydrieig7/mpileaks-1.0.tar.gz
==> Created stage in /usr/workspace/wsa/legendre/spack/var/spack/stage/mpileaks-1.0-otqo2opkhan5ksujt6tpmdftydrieig7
==> Ran patch() for mpileaks
==> Building mpileaks [AutotoolsPackage]
==> Executing phase : 'autoreconf'
==> Executing phase : 'configure'
==> './configure' '--prefix=/usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/mpileaks-1.0-otqo2opkhan5ksujt6tpmdftydrieig7' '--with-adept-utils=/usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/adept-utils-1.0.1-7p7ezxwtajdglj6cmojy2vybjct4j4jz' '--with-callpath=/usr/workspace/wsa/legendre/spack/opt/spack/linux-rhel7-x86_64/gcc-4.9.3/callpath-1.0.2-zm4pf3gasgxeibyu2y262suktvaazube' '--with-stack-start-c=4' '--with-stack-start-fortran=4'

The Spec Object

This tutorial has glossed over a few important features, which weren’t too relevant for mpileaks but may be useful for other packages. There were several places we references the self.spec object. This is a powerful class for querying information about what we’re building. For example, you could use the spec to query information about how a package’s dependencies were built, or what compiler was being used, or what version of a package is being installed. Full documentation can be found in the Packaging Guide, but here’s some quick snippets with common queries:

  • Am I building mpileaks version 1.1 or greater?
if self.spec.satisfies('@1.1:'):
  # Do things needed for 1.1+
  • Is openmpi the MPI I’m building with?
if self.spec['mpi'].name == 'openmpi':
  # Do openmpi things
  • Am I building with gcc version less than 5.0.0:
if self.spec.satisfies('%gcc@:5.0.0'):
  # Add arguments specific to gcc's earlier than 5.0.0
  • Am I built with the debug variant:
if self.spec.satisfies('+debug'):
  # Add -g option to configure flags
  • Is my dyninst dependency greater than version 8.0?
if self.spec['dyninst'].satisfies('@8.0:'):
 # Use newest dyninst options

More examples can be found in the thousands of packages already added to Spack in $SPACK_ROOT/var/spack/repos/builtin/packages.

Good Luck!