SC17: advanced packaging tutorial (#6148)

* First draft of the advanced packaging tutorial

* advanced packaging tutorial: improved phrasing

Thanks Denis and Hartzell!

* Fixed typos + reworded a couple of sentences

2 files changed, 564 insertions, 0 deletions

diff --git a/lib/spack/docs/tutorial.rst b/lib/spack/docs/tutorial.rst
index e6f48fa10e..4bfc772dde 100644
--- a/lib/spack/docs/tutorial.rst
+++ b/lib/spack/docs/tutorial.rst
@@ -45,4 +45,5 @@ Full contents:
 .. toctree::
    tutorial_basics
    tutorial_packaging
+   tutorial_advanced_packaging
    tutorial_modules
diff --git a/lib/spack/docs/tutorial_advanced_packaging.rst b/lib/spack/docs/tutorial_advanced_packaging.rst
new file mode 100644
index 0000000000..901e75bfd7
--- /dev/null
+++ b/lib/spack/docs/tutorial_advanced_packaging.rst
@@ -0,0 +1,563 @@
+.. _advanced-packaging-tutorial:
+
+============================
+Advanced Topics in Packaging
+============================
+
+While you can quickly accomplish most common tasks with what
+was covered in :ref:`packaging-tutorial`, there are times when such
+knowledge won't suffice. Usually this happens for libraries that provide
+more than one API and need to let dependents decide which one to use
+or for packages that provide tools that are invoked at build-time,
+or in other similar situations.
+
+In the following we'll dig into some of the details of package
+implementation that help us deal with these rare, but important,
+occurrences. You can rest assured that in every case Spack remains faithful to
+its philosophy: keep simple things simple, but be flexible enough when
+complex requests arise!
+
+----------------------
+Setup for the tutorial
+----------------------
+
+The simplest way to follow along with this tutorial is to use our Docker image,
+which comes with Spack and various packages pre-installed:
+
+.. code-block:: console
+
+  $ docker pull alalazo/spack:advanced_packaging_tutorial
+  $ docker run --rm -h advanced-packaging-tutorial -it alalazo/spack:advanced_packaging_tutorial
+  root@advanced-packaging-tutorial:/#
+  root@advanced-packaging-tutorial:/# spack find
+  ==> 20 installed packages.
+  -- linux-ubuntu16.04-x86_64 / gcc@5.4.0 -------------------------
+  arpack-ng@3.5.0  hdf5@1.10.1   libpciaccess@0.13.5  libtool@2.4.6  m4@1.4.18  ncurses@6.0          openblas@0.2.20  openssl@1.0.2k     superlu@5.2.1       xz@5.2.3
+  cmake@3.9.4      hwloc@1.11.8  libsigsegv@2.11      libxml2@2.9.4  mpich@3.2  netlib-lapack@3.6.1  openmpi@3.0.0    pkg-config@0.29.2  util-macros@1.19.1  zlib@1.2.11
+
+If you already started the image, you can set the ``EDITOR`` environment
+variable to your preferred editor (``vi``, ``emacs``, and ``nano`` are included in the image)
+and move directly to :ref:`specs_build_interface_tutorial`.
+
+If you choose not to use the Docker image, you can clone the Spack repository
+and build the necessary bits yourself:
+
+.. code-block:: console
+
+  $ git clone https://github.com/spack/spack.git
+  Cloning into 'spack'...
+  remote: Counting objects: 92731, done.
+  remote: Compressing objects: 100% (1108/1108), done.
+  remote: Total 92731 (delta 1964), reused 4186 (delta 1637), pack-reused 87932
+  Receiving objects: 100% (92731/92731), 33.31 MiB | 64.00 KiB/s, done.
+  Resolving deltas: 100% (43557/43557), done.
+  Checking connectivity... done.
+
+  $ cd spack
+  $ git checkout tutorials/advanced_packaging
+  Branch tutorials/advanced_packaging set up to track remote branch tutorials/advanced_packaging from origin.
+  Switched to a new branch 'tutorials/advanced_packaging'
+
+At this point you can install the software that will be used
+during the rest of the tutorial (the output of the commands is omitted
+for the sake of brevity):
+
+.. code-block:: console
+
+  $ spack install openblas
+  $ spack install netlib-lapack
+  $ spack install mpich
+  $ spack install openmpi
+  $ spack install --only=dependencies armadillo ^openblas
+  $ spack install --only=dependencies netcdf
+  $ spack install --only=dependencies elpa
+
+Now, you are ready to set your preferred ``EDITOR`` and continue with
+the rest of the tutorial.
+
+
+.. _specs_build_interface_tutorial:
+
+----------------------
+Spec's build interface
+----------------------
+
+Spack is designed with an emphasis on assigning responsibilities
+to the appropriate entities, as this results in a clearer and more intuitive interface
+for the users.
+When it comes to packaging, one of the most fundamental guideline that
+emerged from this tenet is that:
+
+  *It is a package's responsibility to know
+  every software it directly depends on and to expose to others how to
+  use the services it provides*.
+
+Spec's build interface is a protocol-like implementation of this guideline
+that allows packages to easily query their dependencies,
+and prescribes how they should expose their own build information.
+
+^^^^^^^^^^^^^^^^^^^^
+A motivating example
+^^^^^^^^^^^^^^^^^^^^
+
+We've started work on a package for ``armadillo``. You should open it,
+read through the comment that starts with ``# TUTORIAL:`` and complete
+the ``cmake_args`` section:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack edit armadillo
+
+If you followed the instructions in the package, when you are finished your
+``cmake_args`` method should look like:
+
+.. code-block:: python
+
+  def cmake_args(self):
+        spec = self.spec
+
+        return [
+            # ARPACK support
+            '-DARPACK_LIBRARY={0}'.format(spec['arpack-ng'].libs.joined(";")),
+            # BLAS support
+            '-DBLAS_LIBRARY={0}'.format(spec['blas'].libs.joined(";")),
+            # LAPACK support
+            '-DLAPACK_LIBRARY={0}'.format(spec['lapack'].libs.joined(";")),
+            # SuperLU support
+            '-DSuperLU_INCLUDE_DIR={0}'.format(spec['superlu'].prefix.include),
+            '-DSuperLU_LIBRARY={0}'.format(spec['superlu'].libs.joined(";")),
+            # HDF5 support
+            '-DDETECT_HDF5={0}'.format('ON' if '+hdf5' in spec else 'OFF')
+        ]
+
+As you can see, getting the list of libraries that your dependencies provide
+is as easy as accessing the their ``libs`` attribute. Furthermore, the interface
+remains the same whether you are querying regular or virtual dependencies.
+
+At this point you can complete the installation of ``armadillo`` using ``openblas``
+as a LAPACK provider:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack install armadillo ^openblas
+  ==> pkg-config is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/pkg-config-0.29.2-ae2hwm7q57byfbxtymts55xppqwk7ecj
+  ...
+  ==> superlu is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/superlu-5.2.1-q2mbtw2wo4kpzis2e2n227ip2fquxrno
+  ==> Installing armadillo
+  ==> Using cached archive: /usr/local/var/spack/cache/armadillo/armadillo-8.100.1.tar.xz
+  ==> Staging archive: /usr/local/var/spack/stage/armadillo-8.100.1-n2eojtazxbku6g4l5izucwwgnpwz77r4/armadillo-8.100.1.tar.xz
+  ==> Created stage in /usr/local/var/spack/stage/armadillo-8.100.1-n2eojtazxbku6g4l5izucwwgnpwz77r4
+  ==> Applied patch undef_linux.patch
+  ==> Building armadillo [CMakePackage]
+  ==> Executing phase: 'cmake'
+  ==> Executing phase: 'build'
+  ==> Executing phase: 'install'
+  ==> Successfully installed armadillo
+    Fetch: 0.01s.  Build: 3.96s.  Total: 3.98s.
+  [+] /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/armadillo-8.100.1-n2eojtazxbku6g4l5izucwwgnpwz77r4
+
+Hopefully the installation went fine and the code we added expanded to the right list
+of semicolon separated libraries (you are encouraged to open ``armadillo``'s
+build logs to double check).
+
+If we try to build another version tied to ``netlib-lapack`` we'll
+notice that this time the installation won't complete:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack install  armadillo ^netlib-lapack
+  ==> pkg-config is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/pkg-config-0.29.2-ae2hwm7q57byfbxtymts55xppqwk7ecj
+  ...
+  ==> openmpi is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/openmpi-3.0.0-yo5qkfvumpmgmvlbalqcadu46j5bd52f
+  ==> Installing arpack-ng
+  ==> Using cached archive: /usr/local/var/spack/cache/arpack-ng/arpack-ng-3.5.0.tar.gz
+  ==> Already staged arpack-ng-3.5.0-bloz7cqirpdxj33pg7uj32zs5likz2un in /usr/local/var/spack/stage/arpack-ng-3.5.0-bloz7cqirpdxj33pg7uj32zs5likz2un
+  ==> No patches needed for arpack-ng
+  ==> Building arpack-ng [Package]
+  ==> Executing phase: 'install'
+  ==> Error: RuntimeError: Unable to recursively locate netlib-lapack libraries in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/netlib-lapack-3.6.1-jjfe23wgt7nkjnp2adeklhseg3ftpx6z
+  RuntimeError: RuntimeError: Unable to recursively locate netlib-lapack libraries in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/netlib-lapack-3.6.1-jjfe23wgt7nkjnp2adeklhseg3ftpx6z
+
+  /usr/local/var/spack/repos/builtin/packages/arpack-ng/package.py:105, in install:
+       5             options.append('-DCMAKE_INSTALL_NAME_DIR:PATH=%s/lib' % prefix)
+       6
+       7             # Make sure we use Spack's blas/lapack:
+    >> 8             lapack_libs = spec['lapack'].libs.joined(';')
+       9             blas_libs = spec['blas'].libs.joined(';')
+       10
+       11            options.extend([
+
+  See build log for details:
+    /usr/local/var/spack/stage/arpack-ng-3.5.0-bloz7cqirpdxj33pg7uj32zs5likz2un/arpack-ng-3.5.0/spack-build.out
+
+This is because ``netlib-lapack`` requires extra work, compared to ``openblas``,
+to expose its build information to other packages. Let's edit it:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack edit netlib-lapack
+
+and follow the instructions in the ``# TUTORIAL:`` comment as before.
+What we need to implement is:
+
+.. code-block:: python
+
+  @property
+  def lapack_libs(self):
+      shared = True if '+shared' in self.spec else False
+      return find_libraries(
+          'liblapack', root=self.prefix, shared=shared, recurse=True
+      )
+
+i.e. a property that returns the correct list of libraries for the LAPACK interface.
+Now we can finally install ``armadillo ^netlib-lapack``:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack install  armadillo ^netlib-lapack
+  ...
+
+  ==> Building armadillo [CMakePackage]
+  ==> Executing phase: 'cmake'
+  ==> Executing phase: 'build'
+  ==> Executing phase: 'install'
+  ==> Successfully installed armadillo
+    Fetch: 0.01s.  Build: 3.75s.  Total: 3.76s.
+  [+] /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/armadillo-8.100.1-sxmpu5an4dshnhickh6ykchyfda7jpyn
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+What happens at subscript time?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The example above leaves us with a few questions. How could it be that the
+attribute:
+
+.. code-block:: python
+
+  spec['lapack'].libs
+
+stems from a property of the ``netlib-lapack`` package that has a different name?
+How is it even computed for ``openblas``, given that in its package there's no code
+that deals with finding libraries?
+The answer is that ``libs`` is one of the few properties of specs that follow the
+*build-interface protocol*. The others are currently ``command`` and ``headers``.
+These properties exist only on concrete specs that have been retrieved via the
+subscript notation.
+
+What happens is that, whenever you retrieve a spec using subscripts:
+
+.. code-block:: python
+
+  lapack = spec['lapack']
+
+the key that appears in the query (in this case ``'lapack'``) is attached to the
+returned item. When, later on, you access any of the build-interface attributes, this
+key is used to compute the result according to the following algorithm:
+
+.. code-block:: none
+
+  Given any pair of <query-key> and <build-attribute>:
+
+    1. If <query-key> is the name of a virtual spec and the package
+       providing it has an attribute named '<query-key>_<build-attribute>'
+       return it
+
+    2. Otherwise if the package has an attribute named '<build-attribute>'
+       return that
+
+    3. Otherwise use the default handler for <build-attribute>
+
+Going back to our concrete case this means that, if the spec providing LAPACK
+is ``netlib-lapack``, we are returning the value computed in the ``lapack_libs``
+property. If it is ``openblas``, we are instead resorting to the default handler
+for ``libs`` (which searches for the presence of ``libopenblas`` in the
+installation prefix).
+
+.. note::
+
+  Types commonly returned by build-interface attributes
+    Even though there's no enforcement on it, the type of the objects returned most often when
+    asking for the ``libs`` attributes is :py:class:`LibraryList <llnl.util.filesystem.LibraryList>`.
+    Similarly the usual type returned for ``headers`` is :py:class:`HeaderList <llnl.util.filesystem.HeaderList>`,
+    while for ``command`` is :py:class:`Executable <spack.util.executable.Executable>`. You can refer to
+    these objects' API documentation to discover more about them.
+
+^^^^^^^^^^^^^^^^^^^^^^^
+Extra query parameters
+^^^^^^^^^^^^^^^^^^^^^^^
+
+An advanced feature of the Spec's build-interface protocol is the support
+for extra parameters after the subscript key. In fact, any of the keys used in the query
+can be followed by a comma separated list of extra parameters which can be
+inspected by the package receiving the request to fine-tune a response.
+
+Let's look at an example and try to install ``netcdf``:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack install netcdf
+  ==> libsigsegv is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/libsigsegv-2.11-fypapcprssrj3nstp6njprskeyynsgaz
+  ==> m4 is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/m4-1.4.18-r5envx3kqctwwflhd4qax4ahqtt6x43a
+  ...
+  ==> Error: AttributeError: 'list' object has no attribute 'search_flags'
+  AttributeError: AttributeError: 'list' object has no attribute 'search_flags'
+
+  /usr/local/var/spack/repos/builtin/packages/netcdf/package.py:207, in configure_args:
+       50            # used instead.
+       51            hdf5_hl = self.spec['hdf5:hl']
+       52            CPPFLAGS.append(hdf5_hl.headers.cpp_flags)
+    >> 53            LDFLAGS.append(hdf5_hl.libs.search_flags)
+       54
+       55            if '+parallel-netcdf' in self.spec:
+       56                config_args.append('--enable-pnetcdf')
+
+  See build log for details:
+    /usr/local/var/spack/stage/netcdf-4.4.1.1-gk2xxhbqijnrdwicawawcll4t3c7dvoj/netcdf-4.4.1.1/spack-build.out
+
+We can see from the error that ``netcdf`` needs to know how to link the *high-level interface*
+of ``hdf5``, and thus passes the extra parameter ``hl`` after the request to retrieve it.
+Clearly the implementation in the ``hdf5`` package is not complete, and we need to fix it:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack edit hdf5
+
+If you followed the instructions correctly, the code added to the
+``lib`` property should be similar to:
+
+.. code-block:: python
+  :emphasize-lines: 1
+
+  query_parameters = self.spec.last_query.extra_parameters
+  key = tuple(sorted(query_parameters))
+  libraries = query2libraries[key]
+  shared = '+shared' in self.spec
+  return find_libraries(
+      libraries, root=self.prefix, shared=shared, recurse=True
+  )
+
+where we highlighted the line retrieving  the extra parameters. Now we can successfully
+complete the installation of ``netcdf``:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack install netcdf
+  ==> libsigsegv is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/libsigsegv-2.11-fypapcprssrj3nstp6njprskeyynsgaz
+  ==> m4 is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/m4-1.4.18-r5envx3kqctwwflhd4qax4ahqtt6x43a
+  ...
+  ==> Installing netcdf
+  ==> Using cached archive: /usr/local/var/spack/cache/netcdf/netcdf-4.4.1.1.tar.gz
+  ==> Already staged netcdf-4.4.1.1-gk2xxhbqijnrdwicawawcll4t3c7dvoj in /usr/local/var/spack/stage/netcdf-4.4.1.1-gk2xxhbqijnrdwicawawcll4t3c7dvoj
+  ==> Already patched netcdf
+  ==> Building netcdf [AutotoolsPackage]
+  ==> Executing phase: 'autoreconf'
+  ==> Executing phase: 'configure'
+  ==> Executing phase: 'build'
+  ==> Executing phase: 'install'
+  ==> Successfully installed netcdf
+    Fetch: 0.01s.  Build: 24.61s.  Total: 24.62s.
+  [+] /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/netcdf-4.4.1.1-gk2xxhbqijnrdwicawawcll4t3c7dvoj
+
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Single package providing multiple virtual specs
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+At the close of this tutorial's subsection, it may be useful to see where the
+build-interface protocol shines the most i.e. when it comes to manage packages
+that provide more than one virtual spec. An example of a package of this kind is
+``intel-parallel-studio``, and due to its complexity we'll limit our discussion
+here to just a few considerations (without any hands-on). You can open
+the related ``package.py`` in the usual way:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack edit intel-parallel-studio
+
+As you can see this package provides a lot of virtual specs, and thus it has
+more than one function that enters into the build-interface protocol. These
+functions will be invoked for *exactly the same spec* according to the key used
+by its dependents in the subscript query.
+
+So, for instance, the ``blas_libs`` property will be returned when
+``intel-parallel-studio`` is the BLAS provider in the current DAG and
+is retrieved by a dependent with:
+
+.. code-block:: python
+
+  blas = self.spec['blas']
+  blas_libs = blas.libs
+
+Within the property we inspect various aspects of the current spec:
+
+.. code-block:: python
+
+  @property
+  def blas_libs(self):
+     spec = self.spec
+     prefix = self.prefix
+     shared = '+shared' in spec
+
+     if '+ilp64' in spec:
+         mkl_integer = ['libmkl_intel_ilp64']
+     else:
+         mkl_integer = ['libmkl_intel_lp64']
+     ...
+
+and construct the list of library we need to return accordingly.
+
+What we achieved is that the complexity of dealing with ``intel-parallel-studio``
+is now gathered in the package itself, instead of being spread
+all over its possible dependents.
+Thus, a package that uses MPI or LAPACK doesn't care which implementation it uses,
+as each virtual dependency has
+*a uniform interface* to ask for libraries or headers and manipulate them.
+The packages that provide this virtual spec, on the other hand, have a clear
+way to differentiate their answer to the query [#uniforminterface]_.
+
+.. [#uniforminterface] Before this interface was added, each package that
+   depended on MPI or LAPACK had dozens of lines of code copied from other
+   packages telling it where to find the libraries and what they are called.
+   With the addition of this interface, the virtual dependency itself tells
+   other packages that depend on it where it can find its libraries.
+
+---------------------------
+Package's build environment
+---------------------------
+
+Besides Spec's build interface, Spack provides means to set environment
+variables, either for yourself or for your dependent packages, and to
+attach attributes to your dependents. We'll see them next with the help
+of a few real use cases.
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Set variables at build-time for yourself
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Spack provides a way to manipulate a package's build time and
+run time environments using the
+:py:func:`setup_environment <spack.package.PackageBase.setup_environment>` function.
+Let's try to see how it works by completing the ``elpa`` package:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack edit elpa
+
+In the end your method should look like:
+
+.. code-block:: python
+
+  def setup_environment(self, spack_env, run_env):
+      spec = self.spec
+
+      spack_env.set('CC', spec['mpi'].mpicc)
+      spack_env.set('FC', spec['mpi'].mpifc)
+      spack_env.set('CXX', spec['mpi'].mpicxx)
+      spack_env.set('SCALAPACK_LDFLAGS', spec['scalapack'].libs.joined())
+
+      spack_env.append_flags('LDFLAGS', spec['lapack'].libs.search_flags)
+      spack_env.append_flags('LIBS', spec['lapack'].libs.link_flags)
+
+The two arguments, ``spack_env`` and ``run_env``, are both instances of
+:py:class:`EnvironmentModifications <spack.environment.EnvironmentModifications>` and
+permit you to register modifications to either the build-time or the run-time
+environment of the package, respectively.
+At this point it's possible to proceed with the installation of ``elpa``:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack install elpa
+  ==> pkg-config is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/pkg-config-0.29.2-ae2hwm7q57byfbxtymts55xppqwk7ecj
+  ==> ncurses is already installed in /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/ncurses-6.0-ukq4tccptm2rxd56d2bumqthnpcjzlez
+  ...
+  ==> Executing phase: 'build'
+  ==> Executing phase: 'install'
+  ==> Successfully installed elpa
+    Fetch: 3.94s.  Build: 41.93s.  Total: 45.87s.
+  [+] /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/elpa-2016.05.004-sdbfhwcexg7s2zqf52vssb762ocvklbu
+
+If you had modifications to ``run_env``, those would have appeared e.g. in the module files
+generated for the package.
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Set variables in dependencies at build-time
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Another common occurrence, particularly for packages like ``r`` and ``python``
+that support extensions and for packages that provide build tools,
+is to require *their dependents* to have some environment variables set.
+
+The mechanism is similar to what we just saw, except that we override the
+:py:func:`setup_dependent_environment <spack.package.PackageBase.setup_dependent_environment>`
+function, which takes one additional argument, i.e. the dependent spec that needs the modified
+environment. Let's practice completing the ``mpich`` package:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack edit mpich
+
+Once you're finished the method should look like this:
+
+.. code-block:: python
+
+  def setup_dependent_environment(self, spack_env, run_env, dependent_spec):
+      spack_env.set('MPICC',  join_path(self.prefix.bin, 'mpicc'))
+      spack_env.set('MPICXX', join_path(self.prefix.bin, 'mpic++'))
+      spack_env.set('MPIF77', join_path(self.prefix.bin, 'mpif77'))
+      spack_env.set('MPIF90', join_path(self.prefix.bin, 'mpif90'))
+
+      spack_env.set('MPICH_CC', spack_cc)
+      spack_env.set('MPICH_CXX', spack_cxx)
+      spack_env.set('MPICH_F77', spack_f77)
+      spack_env.set('MPICH_F90', spack_fc)
+      spack_env.set('MPICH_FC', spack_fc)
+
+At this point we can, for instance, install ``netlib-scalapack``:
+
+.. code-block:: console
+
+  root@advanced-packaging-tutorial:/# spack install netlib-scalapack ^mpich
+  ...
+  ==> Created stage in /usr/local/var/spack/stage/netlib-scalapack-2.0.2-km7tsbgoyyywonyejkjoojskhc5knz3z
+  ==> No patches needed for netlib-scalapack
+  ==> Building netlib-scalapack [CMakePackage]
+  ==> Executing phase: 'cmake'
+  ==> Executing phase: 'build'
+  ==> Executing phase: 'install'
+  ==> Successfully installed netlib-scalapack
+    Fetch: 0.01s.  Build: 3m 59.86s.  Total: 3m 59.87s.
+  [+] /usr/local/opt/spack/linux-ubuntu16.04-x86_64/gcc-5.4.0/netlib-scalapack-2.0.2-km7tsbgoyyywonyejkjoojskhc5knz3z
+
+
+and double check the environment logs to verify that every variable was
+set to the correct value. More complicated examples of the use of this function
+may be found in the ``r`` and ``python`` package.
+
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Attach attributes to other packages
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Build tools usually also provide a set of executables that can be used
+when another package is being installed. Spack gives the opportunity
+to monkey-patch dependent modules and attach attributes to them. This
+helps make the packager experience as similar as possible to what would
+have been the manual installation of the same package.
+
+An example here is the ``automake`` package, which overrides
+:py:func:`setup_dependent_package <spack.package.PackageBase.setup_dependent_package>`:
+
+.. code-block:: python
+
+  def setup_dependent_package(self, module, dependent_spec):
+      # Automake is very likely to be a build dependency,
+      # so we add the tools it provides to the dependent module
+      executables = ['aclocal', 'automake']
+      for name in executables:
+          setattr(module, name, self._make_executable(name))
+
+so that every other package that depends on it can use directly ``aclocal``
+and ``automake`` with the usual function call syntax of :py:class:`Executable <spack.util.executable.Executable>`:
+
+.. code-block:: python
+
+  aclocal('--force')
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