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Developer Workflows Tutorial

This tutorial will guide you through the process of using the spack dev-build command to manage dependencies while developing software. This will allow you to install a package from local source, develop that source code, and iterate on the different phases of your build system as necessary.

Installing from local source

The spack install command, as you know, fetches source code from a mirror or the internet before building and installing your package. As developers, we want to build from local source, which we will constantly change, build, and test.

Let's imagine for a second we're working on hwloc. hwloc is a tool used by MPI libraries to understand the hierarchy (NUMA, sockets, etc.) of modern node architectures. It's a pretty low-level library, but we've chosen it as an example here because it's quick to build, and we already have binary packages for its dependencies:

.. graphviz::

    digraph G {
    labelloc = "b"
    rankdir = "TB"
    ranksep = "1"
    edge[
       penwidth=4  ]
    node[
       fontname=Monaco,
       penwidth=4,
       fontsize=24,
       margin=.2,
       shape=box,
       fillcolor=lightblue,
       style="rounded,filled"  ]

    "hwloc" -> "libxml2"
    "libxml2" -> "xz"
    "automake" -> "perl"
    "libxml2" -> "pkgconf"
    "autoconf" -> "perl"
    "libpciaccess" -> "libtool"
    "hwloc" -> "pkgconf"
    "libpciaccess" -> "util-macros"
    "autoconf" -> "m4"
    "hwloc" -> "m4"
    "hwloc" -> "automake"
    "automake" -> "autoconf"
    "hwloc" -> "libtool"
    "libpciaccess" -> "pkgconf"
    "ncurses" -> "pkgconf"
    "libxml2" -> "libiconv"
    "perl" -> "gdbm"
    "hwloc" -> "libpciaccess"
    "gdbm" -> "readline"
    "libtool" -> "m4"
    "hwloc" -> "autoconf"
    "m4" -> "libsigsegv"
    "readline" -> "ncurses"
    "libxml2" -> "zlib"
  }


.. literalinclude:: outputs/dev/setup-hwloc.out
   :language: console

Here we have the local hwloc source that we've been working on. If we want to build and install it, we can do so using the spack dev-build command. Note that we need to provide a version in the spec we pass to spack dev-build. By default, the spack dev-build command will print verbose output from the build system to the console.

.. literalinclude:: outputs/dev/dev-build-1.out
   :language: console

Done! hwloc is installed.

So what's going on here? When we use the spack dev-build command, Spack still manages the package's dependencies as it would for the spack install command. The dependencies for hwloc are all installed, either from binary or source, if they were not already. Instead of downloading the source code for hwloc, Spack constructed a stage in the current directory to use the local source. Spack then constructed the build environment and arguments for the hwloc build system as it would for the spack install command. The resulting installation is added to Spack's database as usual, and post-install hooks including modulefile generation are ran as well.

Development iteration cycles

Generally, as developers, we only want to configure our package once, and then we want to iterate developing and building our code, before installing it once if at all. We can do this in Spack using the -u/--until option with the spack dev-build command. To do this we need to know the phases of the build that Spack will use. Fortunately, as experienced hwloc developers we all happen to know that those phases are autoreconf, configure, build, and install. If we don't remember the phases, we could find out using the spack info command.

.. literalinclude:: outputs/dev/info.out
   :language: console

We will tell Spack to stop installing hwloc after the configure stage. This will execute exactly the same as before, except it will stop the installation after the listed, in our case configure, phase completes. We will also tell Spack to launch a subshell in the build environment, so that we can use the hwloc build system manually as Spack would use it.

.. literalinclude:: outputs/dev/dev-build-2.out
   :language: console

Now, we can develop our code. For the sake of this demo, we're just going to intentionally introduce an error. Let's edit a file and remove the first semi-colon we find.

.. literalinclude:: outputs/dev/edit-1.out
   :language: console

To build our code, we have a couple options. We could use spack dev-build and the -u option to configure and build our code, but we've already configured our code, and the changes we made don't affect the build system. Instead, let's run our build system directly -- we are developers of this code now, after all. If you forgot the --drop-in option above, you can use spack build-env hwloc@master -- bash to launch it now.

.. literalinclude:: outputs/dev/hand-build-1.out
   :language: console

This is exactly what we'd expect, since we broke the code on purpose. Now let's fix it and rebuild directly.

.. literalinclude:: outputs/dev/hand-build-2.out
   :language: console

We've now used Spack to install all of our dependencies and configure our code, but we can have a faster development cycle using our build system directly.

Workflow Summary

Use the spack dev-build command with the -u/--until and --drop-in options to setup all of your dependencies and the build environment with Spack, and iterate using your native build system as Spack would use it.