This guide is intended for people who want to work on Spack itself. If you just want to develop packages, see the Packaging Guide.
Spack is designed with three separate roles in mind:
- Users, who need to install software without knowing all the details about how it is built.
- Packagers who know how a particular software package is built and encode this information in package files.
- Developers who work on Spack, add new features, and try to make the jobs of packagers and users easier.
Users could be end users installing software in their home directory, or administrators installing software to a shared directory on a shared machine. Packagers could be administrators who want to automate software builds, or application developers who want to make their software more accessible to users.
As you might expect, there are many types of users with different
levels of sophistication, and Spack is designed to accommodate both
simple and complex use cases for packages. A user who only knows that
he needs a certain package should be able to type something simple,
spack install <package name>, and get the package that he
wants. If a user wants to ask for a specific version, use particular
compilers, or build several versions with different configurations,
then that should be possible with a minimal amount of additional
This gets us to the two key concepts in Spack’s software design:
- Specs: expressions for describing builds of software, and
- Packages: Python modules that build software according to a spec.
A package is a template for building particular software, and a spec as a descriptor for one or more instances of that template. Users express the configuration they want using a spec, and a package turns the spec into a complete build.
The obvious difficulty with this design is that users under-specify what they want. To build a software package, the package object needs a complete specification. In Spack, if a spec describes only one instance of a package, then we say it is concrete. If a spec could describes many instances, (i.e. it is under-specified in one way or another), then we say it is abstract.
Spack’s job is to take an abstract spec from the user, find a concrete spec that satisfies the constraints, and hand the task of building the software off to the package object. The rest of this document describes all the pieces that come together to make that happen.
So that you can familiarize yourself with the project, we’ll start with a high level view of Spack’s directory structure:
spack/ <- installation root bin/ spack <- main spack executable etc/ spack/ <- Spack config files. Can be overridden by files in ~/.spack. var/ spack/ <- build & stage directories repos/ <- contains package repositories builtin/ <- pkg repository that comes with Spack repo.yaml <- descriptor for the builtin repository packages/ <- directories under here contain packages cache/ <- saves resources downloaded during installs opt/ spack/ <- packages are installed here lib/ spack/ docs/ <- source for this documentation env/ <- compiler wrappers for build environment external/ <- external libs included in Spack distro llnl/ <- some general-use libraries spack/ <- spack module; contains Python code cmd/ <- each file in here is a spack subcommand compilers/ <- compiler description files test/ <- unit test modules util/ <- common code
Spack is designed so that it could live within a standard UNIX
directory hierarchy, so
opt all contain a
spack subdirectory in case
Spack is installed alongside other software. Most of the interesting
parts of Spack live in
Spack has one directory layout and there is no install process.
Most Python programs don’t look like this (they use distutils,
etc.) but we wanted to make Spack very easy to use. The simple layout
spares users from the need to install Spack into a Python environment.
Many users don’t have write access to a Python installation, and installing
an entire new instance of Python to bootstrap Spack would be very complicated.
Users should not have to install a big, complicated package to
use the thing that’s supposed to spare them from the details of big,
complicated packages. The end result is that Spack works out of the
box: clone it and add
bin to your PATH and you’re ready to go.
This section gives an overview of the various Python modules in Spack, grouped by functionality.
- Handles creating temporary directories for builds.
- This contains utility functions used by the compiler wrapper script,
- Classes that control the way an installation directory is laid out.
Create more implementations of this to change the hierarchy and
naming scheme in
- Implements Spack’s test suite. Add a module and put its name in
the test suite in
__init__.pyto add more unit tests.
- This is a fake package hierarchy used to mock up packages for Spack’s test suite.
- URL parsing, for deducing names and versions of packages from tarball URLs.
SpackError, the base class for Spack’s exception hierarchy.
- Basic output functions for all of the messages Spack writes to the terminal.
- Implements a color formatting syntax used by
- In this package are a number of utility modules for the rest of Spack.
Most spack commands look something like this:
- Parse an abstract spec (or specs) from the command line,
- Normalize the spec based on information in package files,
- Concretize the spec according to some customizable policies,
- Instantiate a package based on the spec, and
- Call methods (e.g.,
install()) on the package object.
The information in Package files is used at all stages in this process.
Conceptually, packages are overloaded. They contain:
Adding a new command to Spack is easy. Simply add a
<name>.py file to
<name> is the name of the subcommand.
At the bare minimum, two functions are required in this file:
Unless your command doesn’t accept any arguments, a
function is required to define what arguments and flags your command takes.
See the Argparse documentation
for more details on how to add arguments.
Some commands have a set of subcommands, like
spack compiler find or
spack module lmod refresh. You can add subparsers to your parser to handle
this. Check out
spack edit --command compiler for an example of this.
A lot of commands take the same arguments and flags. These arguments should
be defined in
lib/spack/spack/cmd/common/arguments.py so that they don’t
need to be redefined in multiple commands.
In order to run your command, Spack searches for a function with the same
name as your command in
<name>.py. This is the main method for your
command, and can call other helper methods to handle common tasks.
Remember, before adding a new command, think to yourself whether or not this new command is actually necessary. Sometimes, the functionality you desire can be added to an existing command. Also remember to add unit tests for your command. If it isn’t used very frequently, changes to the rest of Spack can cause your command to break without sufficient unit tests to prevent this from happening.
Whenever you add/remove/rename a command or flags for an existing command, make sure to update Spack’s Bash tab completion script.
spack python is a command that lets you import and debug things as if
you were in a Spack interactive shell. Without any arguments, it is similar
to a normal interactive Python shell, except you can import spack and any
other Spack modules:
$ spack python Spack version 0.10.0 Python 2.7.13, Linux x86_64 >>> from spack.version import Version >>> a = Version('1.2.3') >>> b = Version('1_2_3') >>> a == b True >>> c = Version('1.2.3b') >>> c > a True >>>
You can also run a single command:
$ spack python -c 'import distro; distro.linux_distribution()' ('Fedora', '25', 'Workstation Edition')
or a file:
$ spack python ~/test_fetching.py
just like you would with the normal
A package containing a single URL can be used to download several different
versions of the package. If you’ve ever wondered how this works, all of the
magic is in
spack.url. This module contains methods for extracting
the name and version of a package from its URL. The name is used by
spack create to guess the name of the package. By determining the version
from the URL, Spack can replace it with other versions to determine where to
download them from.
The regular expressions in
are used to extract the name and version, but they aren’t perfect. In order
to debug Spack’s URL parsing support, the
spack url command can be used.
spack url parse¶
If you need to debug a single URL, you can use the following command:
$ spack url parse http://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.0.tar.gz ==> Parsing URL: http://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.0.tar.gz ==> Matched version regex 0: r'^[a-zA-Z+._-]+[._-]v?(\\d[\\d._-]*)$' ==> Matched name regex 10: r'^([A-Za-z\\d+\\._-]+)$' ==> Detected: http://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.0.tar.gz ---- ~~~~~ name: ruby version: 2.2.0 ==> Substituting version 9.9.9b: http://cache.ruby-lang.org/pub/ruby/2.2/ruby-9.9.9b.tar.gz ---- ~~~~~~
You’ll notice that the name and version of this URL are correctly detected,
and you can even see which regular expressions it was matched to. However,
you’ll notice that when it substitutes the version number in, it doesn’t
9.9 where we would expect
9.9.9b to live.
This particular package may require a
This command also accepts a
--spider flag. If provided, Spack searches
for other versions of the package and prints the matching URLs.
spack url list¶
This command lists every URL in every package in Spack. If given the
--extrapolation flags, it also colors the part of
the string that it detected to be the name and version. The
--incorrect-version flags can be used to
print URLs that were not being parsed correctly.
spack url summary¶
This command attempts to parse every URL for every package in Spack and prints a summary of how many of them are being correctly parsed. It also prints a histogram showing which regular expressions are being matched and how frequently:
$ spack url summary ==> Generating a summary of URL parsing in Spack... Total URLs found: 4376 Names correctly parsed: 3948/4376 (90.22%) Versions correctly parsed: 4063/4376 (92.85%) ==> Statistics on name regular expressions: Index Right Wrong Total Regular Expression 0 1109 151 1260 r'github\\.com/[^/]+/([^/]+)' 1 6 0 6 r'gitlab[^/]+/api/v4/projects/[^/]+%2F([^/]+)' 2 22 2 24 r'gitlab[^/]+/(?!api/v4/projects)[^/]+/([^/]+)' 3 11 5 16 r'bitbucket\\.org/[^/]+/([^/]+)' 4 899 2 901 r'pypi\\.(?:python\\.org|io)/packages/source/[A-Za-z\\d]/([^/]+)' 6 8 0 8 r'\\?f=([A-Za-z\\d+-]+)$' 7 11 0 11 r'\\?package=([A-Za-z\\d+-]+)' 8 2 0 2 r'\\?package=([A-Za-z\\d]+)' 9 0 2 2 r'([^/]+)/download.php$' 10 1880 261 2141 r'^([A-Za-z\\d+\\._-]+)$' ==> Statistics on version regular expressions: Index Right Wrong Total Regular Expression 0 2867 41 2908 r'^[a-zA-Z+._-]+[._-]v?(\\d[\\d._-]*)$' 1 829 10 839 r'^v?(\\d[\\d._-]*)$' 2 12 17 29 r'^[a-zA-Z+]*(\\d[\\da-zA-Z]*)$' 3 8 14 22 r'^[a-zA-Z+-]*(\\d[\\da-zA-Z-]*)$' 4 3 99 102 r'^[a-zA-Z+_]*(\\d[\\da-zA-Z_]*)$' 5 43 22 65 r'^[a-zA-Z+.]*(\\d[\\da-zA-Z.]*)$' 6 167 7 174 r'^[a-zA-Z\\d+-]+-v?(\\d[\\da-zA-Z.]*)$' 7 1 0 1 r'^[a-zA-Z\\d+-]+-v?(\\d[\\da-zA-Z_]*)$' 8 22 1 23 r'^[a-zA-Z\\d+_]+_v?(\\d[\\da-zA-Z.]*)$' 9 0 2 2 r'^[a-zA-Z\\d+_]+\\.v?(\\d[\\da-zA-Z.]*)$' 11 30 40 70 r'^(?:[a-zA-Z\\d+-]+-)?v?(\\d[\\da-zA-Z.-]*)$' 12 3 0 3 r'^[a-zA-Z+]+v?(\\d[\\da-zA-Z.-]*)$' 13 4 2 6 r'^[a-zA-Z\\d+_]+-v?(\\d[\\da-zA-Z.]*)$' 14 20 4 24 r'^[a-zA-Z\\d+.]+_v?(\\d[\\da-zA-Z.-]*)$' 15 1 0 1 r'^[a-zA-Z\\d+-]+-v?(\\d[\\da-zA-Z._]*)$' 16 1 1 2 r'^[a-zA-Z\\d+._]+-v?(\\d[\\da-zA-Z.]*)$' 17 5 0 5 r'^[a-zA-Z+-]+(\\d[\\da-zA-Z._]*)$' 18 1 2 3 r'^[a-zA-Z\\d+_-]+-v?(\\d[\\da-zA-Z.]*)$' 19 0 1 1 r'bzr(\\d[\\da-zA-Z._-]*)$' 20 8 1 9 r'[?&](?:sha|ref|version)=[a-zA-Z\\d+-]*[_-]?v?(\\d[\\da-zA-Z._-]*)$' 21 19 0 19 r'[?&](?:filename|f|get)=[a-zA-Z\\d+-]+[_-]v?(\\d[\\da-zA-Z.]*)' 22 8 0 8 r'github\\.com/[^/]+/[^/]+/releases/download/[a-zA-Z+._-]*v?(\\d[\\da-zA-Z._-]*)/' 23 11 5 16 r'(\\d[\\da-zA-Z._-]*)/[^/]+$'
This command is essential for anyone adding or changing the regular expressions that parse names and versions. By running this command before and after the change, you can make sure that your regular expression fixes more packages than it breaks.
Spack has some limited built-in support for profiling, and can report
statistics using standard Python timing tools. To use this feature,
--profile to Spack on the command line, before any subcommands.
spack --profile output looks like this:
$ spack --profile graph hdf5 o hdf5 |\ | o openmpi |/| | |\ | | |\ | | | o hwloc | | |/| | |/|/| | | | |\ | | | o | libxml2 | |_|/| | |/| |/| | | |/| | | | | | |\ \ o | | | | | zlib / / / / / | | o | | xz | | / / | | | o libpciaccess | |_|/| |/| | | | | | |\ | | | o | util-macros | | | / ...
The bottom of the output shows the top most time consuming functions, slowest on top. The profiling support is from Python’s built-in tool, cProfile.
This section documents Spack’s release process. It is intended for project maintainers, as the tasks described here require maintainer privileges on the Spack repository. For others, we hope this section at least provides some insight into how the Spack project works.
o branch: develop (latest version) | o merge v0.14.1 into develop |\ | o branch: releases/v0.14, tag: v0.14.1 o | merge v0.14.0 into develop |\| | o tag: v0.14.0 |/ o merge v0.13.2 into develop |\ | o branch: releases/v0.13, tag: v0.13.2 o | merge v0.13.1 into develop |\| | o tag: v0.13.1 o | merge v0.13.0 into develop |\| | o tag: v0.13.0 o | | o |/ o
develop branch has the latest contributions, and nearly all pull
Each Spack release series also has a corresponding branch, e.g.
0.14.x versions of Spack, and
0.13.x versions. A major release is the first
tagged version on a release branch. Minor releases are back-ported from
develop onto release branches. This is typically done by cherry-picking
bugfix commits off of
To avoid version churn for users of a release series, minor releases should not make changes that would change the concretization of packages. They should generally only contain fixes to the Spack core.
Both major and minor releases are tagged. After each release, we merge
the release branch back into
develop so that the version bump and any
other release-specific changes are visible in the mainline. As a
convenience, we also tag the latest release as
so that users can easily check it out to get the latest
stable version. See Updating releases/latest and develop for more details.
Scheduling work for releases¶
We schedule work for releases by creating GitHub projects. At any time, there may be several open release projects. For example, here are two releases (from some past version of the page linked above):
Here, there’s one release in progress for
0.15.1 and another for
0.16.0. Each of these releases has a project board containing issues
and pull requests. GitHub shows a status bar with completed work in
green, work in progress in purple, and work not started yet in gray, so
it’s fairly easy to see progress.
Spack’s project boards are not firm commitments, and we move work between releases frequently. If we need to make a release and some tasks are not yet done, we will simply move them to next minor or major release, rather than delaying the release to complete them.
For more on using GitHub project boards, see GitHub’s documentation.
Making Major Releases¶
Assuming you’ve already created a project board and completed the work for a major release, the steps to make the release are as follows:
Create two new project boards:
- One for the next major release
- One for the next point release
Move any tasks that aren’t done yet to one of the new project boards. Small bugfixes should go to the next point release. Major features, refactors, and changes that could affect concretization should go in the next major release.
Create a branch for the release, based on
$ git checkout -b releases/v0.15 develop
For a version
vX.Y.Z, the branch’s name should be
releases/vX.Y. That is, you should create a
releases/vX.Ybranch if you are preparing the
Bump the version in
lib/spack/spack/__init__.py. See this example from 0.13.0
Update the release version lists in these files to include the new version:
CHANGELOG.mdwith major highlights in bullet form. Use proper markdown formatting, like this example from 0.15.0.
Push the release branch to GitHub.
Make sure CI passes on the release branch, including:
- Regular unit tests
- Build tests
- The E4S pipeline at gitlab.spack.io
If CI is not passing, submit pull requests to
developas normal and keep rebasing the release branch on
developuntil CI passes.
Follow the steps in Publishing a release on GitHub.
Follow the steps in Updating releases/latest and develop.
Follow the steps in Announcing a release.
Making Point Releases¶
This assumes you’ve already created a project board for a point release and completed the work to be done for the release. To make a point release:
Create one new project board for the next point release.
Move any cards that aren’t done yet to the next project board.
Check out the release branch (it should already exist). For the
X.Y.Zrelease, the release branch is called
v0.15.1, you would check out
$ git checkout releases/v0.15
Cherry-pick each pull request in the
Donecolumn of the release project onto the release branch.
This is usually fairly simple since we squash the commits from the vast majority of pull requests, which means there is only one commit per pull request to cherry-pick. For example, this pull request has three commits, but the were squashed into a single commit on merge. You can see the commit that was created here:
You can easily cherry pick it like this (assuming you already have the release branch checked out):
$ git cherry-pick 7e46da7
For pull requests that were rebased, you’ll need to cherry-pick each rebased commit individually. There have not been any rebased PRs like this in recent point releases.
It is important to cherry-pick commits in the order they happened, otherwise you can get conflicts while cherry-picking. When cherry-picking onto a point release, look at the merge date, not the number of the pull request or the date it was opened.
Sometimes you may still get merge conflicts even if you have cherry-picked all the commits in order. This generally means there is some other intervening pull request that the one you’re trying to pick depends on. In these cases, you’ll need to make a judgment call:
- If the dependency is small, you might just cherry-pick it, too. If you do this, add it to the release board.
- If it is large, then you may decide that this fix is not worth including in a point release, in which case you should remove it from the release project.
- You can always decide to manually back-port the fix to the release branch if neither of the above options makes sense, but this can require a lot of work. It’s seldom the right choice.
Bump the version in
lib/spack/spack/__init__.py. See this example from 0.14.1.
Updaate the release version lists in these files to include the new version:
TODO: We should get rid of this step in some future release.
CHANGELOG.mdwith a list of bugfixes. This is typically just a summary of the commits you cherry-picked onto the release branch. See the changelog from 0.14.1.
Push the release branch to GitHub.
Make sure CI passes on the release branch, including: * Regular unit tests * Build tests * The E4S pipeline at gitlab.spack.io
If CI does not pass, you’ll need to figure out why, and make changes to the release branch until it does. You can make more commits, modify or remove cherry-picked commits, or cherry-pick more from
developto make this happen.
Follow the steps in Publishing a release on GitHub.
Follow the steps in Updating releases/latest and develop.
Follow the steps in Announcing a release.
Publishing a release on GitHub¶
Go to github.com/spack/spack/releases and click
Draft a new release. Set the following:
Tag versionshould start with
vand contain all three parts of the version, .g.
v0.15.1. This is the name of the tag that will be created.
Targetshould be the
Release titleshould be
vX.Y.Z(To match the tag, e.g.,
- For the text, paste the latest release markdown from your
You can save the draft and keep coming back to this as you prepare the release.
When you are done, click
Immediately after publishing, go back to github.com/spack/spack/releases and download the auto-generated
.tar.gzfile for the release. It’s the
Source code (tar.gz)link.
Editon the release you just did and attach the downloaded release tarball as a binary. This does two things:
- Makes sure that the hash of our releases doesn’t change over time. GitHub sometimes annoyingly changes they way they generate tarballs, and then hashes can change if you rely on the auto-generated tarball links.
- Gets us download counts on releases visible through the GitHub
API. GitHub tracks downloads of artifacts, but not the source
links. See the releases
page and search
download_countto see this.
Go to readthedocs.org and activate the release tag. This builds the documentation and makes the released version selectable in the versions menu.
Updating releases/latest and develop¶
If the new release is the highest Spack release yet, you should
also tag it as
releases/latest. For example, suppose the highest
release is currently
- If you are releasing
0.16.0, then you should tag it with
releases/latest, as these are higher than
- If you are making a new release of an older major version of Spack, e.g.
0.14.4, then you should not tag it as
releases/latest(as there are newer major versions).
releases/latest, do this:$ git checkout releases/vX.Y # vX.Y is the new release's branch $ git tag --force releases/latest $ git push --tags
gitoverwrite the existing
releases/latesttag with the new one.
We also merge each release that we tag as
Make sure to do this with a merge commit:
$ git checkout develop $ git merge --no-ff vX.Y.Z # vX.Y.Z is the new release's tag $ git push
We merge back to
develop because it:
- updates the version and
- ensures that your release tag is reachable from the head of
We must use a real merge commit (via the
--no-ff option) because it
ensures that the release tag is reachable from the tip of
This is necessary for
spack -V to work properly – it uses
describe --tags to find the last reachable tag in the repository and
reports how far we are from it. For example:
$ spack -V 0.14.2-1486-b80d5e74e5
This says that we are at commit
b80d5e74e5, which is 1,486 commits
ahead of the
We put this step last in the process because it’s best to do it only once the release is complete and tagged. If you do it before you’ve tagged the release and later decide you want to tag some later commit, you’ll need to merge again.
Announcing a release¶
We announce releases in all of the major Spack communication channels. Publishing the release takes care of GitHub. The remaining channels are Twitter, Slack, and the mailing list. Here are the steps:
- Make a tweet to announce the release. It should link to the release’s page on GitHub. You can base it on this example tweet.
#generalon Slack (spackpm.slack.com) with a link to the tweet. The tweet will be shown inline so that you do not have to retype your release announcement.
- Email the Spack mailing list to let them know about the release. As with the tweet, you likely want to link to the release’s page on GitHub. It’s also helpful to include some information directly in the email. You can base yours on this example email.
Once you’ve announced the release, congratulations, you’re done! You’ve finished making the release!