From 45c675fe7ff69408e4f407a9c5eb8f92f746faf8 Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Mon, 25 Jan 2016 10:26:35 -0500
Subject: [PATCH] spack: introduce dependency types

deptypes: allow for different queries

For things like Python modules, they are required for the build and
runtime, but rather than adding a new parameter for what to query across
the dependency DAG, just expose the recursive query parameter.
---
 lib/spack/docs/packaging_guide.rst            |  25 ++
 lib/spack/spack/__init__.py                   |   3 +-
 lib/spack/spack/build_environment.py          |  14 +-
 lib/spack/spack/cmd/fetch.py                  |   2 +-
 lib/spack/spack/cmd/info.py                   |  14 +-
 lib/spack/spack/cmd/mirror.py                 |   2 +-
 lib/spack/spack/cmd/module.py                 |   2 +-
 lib/spack/spack/cmd/package-list.py           |  14 +-
 lib/spack/spack/cmd/test-install.py           |   7 +-
 lib/spack/spack/concretize.py                 |  10 +-
 lib/spack/spack/database.py                   |  22 +-
 lib/spack/spack/directives.py                 |  39 +-
 lib/spack/spack/graph.py                      |  10 +-
 lib/spack/spack/modules.py                    |   2 +-
 lib/spack/spack/package.py                    |  20 +-
 lib/spack/spack/spec.py                       | 348 +++++++++++++-----
 lib/spack/spack/test/cmd/test_install.py      |  33 +-
 lib/spack/spack/test/concretize.py            |  24 +-
 lib/spack/spack/test/mock_packages_test.py    |   8 +-
 lib/spack/spack/test/spec_dag.py              |  88 ++++-
 .../packages/cmake-client/package.py          |   2 +-
 .../builtin.mock/packages/dtbuild1/package.py |  18 +
 .../builtin.mock/packages/dtbuild2/package.py |  13 +
 .../builtin.mock/packages/dtbuild3/package.py |  13 +
 .../builtin.mock/packages/dtlink1/package.py  |  15 +
 .../builtin.mock/packages/dtlink2/package.py  |  13 +
 .../builtin.mock/packages/dtlink3/package.py  |  16 +
 .../builtin.mock/packages/dtlink4/package.py  |  13 +
 .../builtin.mock/packages/dtlink5/package.py  |  13 +
 .../builtin.mock/packages/dtrun1/package.py   |  16 +
 .../builtin.mock/packages/dtrun2/package.py   |  13 +
 .../builtin.mock/packages/dtrun3/package.py   |  15 +
 .../builtin.mock/packages/dttop/package.py    |  17 +
 .../builtin.mock/packages/dtuse/package.py    |  15 +
 34 files changed, 697 insertions(+), 182 deletions(-)
 create mode 100644 var/spack/repos/builtin.mock/packages/dtbuild1/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtbuild2/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtbuild3/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtlink1/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtlink2/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtlink3/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtlink4/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtlink5/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtrun1/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtrun2/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtrun3/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dttop/package.py
 create mode 100644 var/spack/repos/builtin.mock/packages/dtuse/package.py

diff --git a/lib/spack/docs/packaging_guide.rst b/lib/spack/docs/packaging_guide.rst
index 0f549e2957..a0d0feabbd 100644
--- a/lib/spack/docs/packaging_guide.rst
+++ b/lib/spack/docs/packaging_guide.rst
@@ -1286,6 +1286,31 @@ command line to find installed packages or to install packages with
 particular constraints, and package authors can use specs to describe
 relationships between packages.
 
+Additionally, dependencies may be specified for specific use cases:
+
+.. code-block:: python
+
+    depends_on("cmake", type="build")
+    depends_on("libelf", type=("build", "link"))
+    depends_on("python", type="run")
+
+The dependency types are:
+
+  * **"build"**: made available during the project's build. The package will
+    be added to ``PATH``, the compiler include paths, and ``PYTHONPATH``.
+    Other projects which depend on this one will not have these modified
+    (building project X doesn't need project Y's build dependencies).
+  * **"link"**: the project is linked to by the project. The package will be
+    added to the current package's ``rpath``.
+  * **"run"**: the project is used by the project at runtime. The package will
+    be added to ``PATH`` and ``PYTHONPATH``.
+
+If not specified, ``type`` is assumed to be ``("build", "link")``. This is the
+common case for compiled language usage. Also available are the aliases
+``alldeps`` for all dependency types and ``nolink`` (``("build", "run")``) for
+use by dependencies which are not expressed via a linker (e.g., Python or Lua
+module loading).
+
 .. _setup-dependent-environment:
 
 ``setup_dependent_environment()``
diff --git a/lib/spack/spack/__init__.py b/lib/spack/spack/__init__.py
index 20c9934704..d67585aac4 100644
--- a/lib/spack/spack/__init__.py
+++ b/lib/spack/spack/__init__.py
@@ -177,10 +177,11 @@
 #       should live.  This file is overloaded for spack core vs. for packages.
 #
 __all__ = ['Package', 'StagedPackage', 'CMakePackage', \
-    'Version', 'when', 'ver']
+    'Version', 'when', 'ver', 'alldeps', 'nolink']
 from spack.package import Package, ExtensionConflictError
 from spack.package import StagedPackage, CMakePackage
 from spack.version import Version, ver
+from spack.spec import DependencySpec, alldeps, nolink
 from spack.multimethod import when
 
 import llnl.util.filesystem
diff --git a/lib/spack/spack/build_environment.py b/lib/spack/spack/build_environment.py
index fe5186a7d7..93fb0690f7 100644
--- a/lib/spack/spack/build_environment.py
+++ b/lib/spack/spack/build_environment.py
@@ -254,7 +254,8 @@ def set_build_environment_variables(pkg, env, dirty=False):
     env.set_path(SPACK_ENV_PATH, env_paths)
 
     # Prefixes of all of the package's dependencies go in SPACK_DEPENDENCIES
-    dep_prefixes = [d.prefix for d in pkg.spec.traverse(root=False)]
+    dep_prefixes = [d.prefix
+                    for d in pkg.spec.traverse(root=False, deptype='build')]
     env.set_path(SPACK_DEPENDENCIES, dep_prefixes)
     # Add dependencies to CMAKE_PREFIX_PATH
     env.set_path('CMAKE_PREFIX_PATH', dep_prefixes)
@@ -337,10 +338,6 @@ def set_module_variables_for_package(pkg, module):
     # Don't use which for this; we want to find it in the current dir.
     m.configure = Executable('./configure')
 
-    # TODO: shouldn't really use "which" here.  Consider adding notion
-    # TODO: of build dependencies, as opposed to link dependencies.
-    # TODO: Currently, everything is a link dependency, but tools like
-    # TODO: this shouldn't be.
     m.cmake = Executable('cmake')
     m.ctest = Executable('ctest')
 
@@ -388,9 +385,10 @@ def set_module_variables_for_package(pkg, module):
 def get_rpaths(pkg):
     """Get a list of all the rpaths for a package."""
     rpaths = [pkg.prefix.lib, pkg.prefix.lib64]
-    rpaths.extend(d.prefix.lib for d in pkg.spec.dependencies.values()
+    deps = pkg.spec.dependencies(deptype='link')
+    rpaths.extend(d.prefix.lib for d in deps
                   if os.path.isdir(d.prefix.lib))
-    rpaths.extend(d.prefix.lib64 for d in pkg.spec.dependencies.values()
+    rpaths.extend(d.prefix.lib64 for d in deps
                   if os.path.isdir(d.prefix.lib64))
     # Second module is our compiler mod name. We use that to get rpaths from
     # module show output.
@@ -449,7 +447,7 @@ def setup_package(pkg, dirty=False):
     load_external_modules(pkg)
     # traverse in postorder so package can use vars from its dependencies
     spec = pkg.spec
-    for dspec in pkg.spec.traverse(order='post', root=False):
+    for dspec in pkg.spec.traverse(order='post', root=False, deptype='build'):
         # If a user makes their own package repo, e.g.
         # spack.repos.mystuff.libelf.Libelf, and they inherit from
         # an existing class like spack.repos.original.libelf.Libelf,
diff --git a/lib/spack/spack/cmd/fetch.py b/lib/spack/spack/cmd/fetch.py
index e40caaa234..1afc51d9fa 100644
--- a/lib/spack/spack/cmd/fetch.py
+++ b/lib/spack/spack/cmd/fetch.py
@@ -51,7 +51,7 @@ def fetch(parser, args):
     for spec in specs:
         if args.missing or args.dependencies:
             to_fetch = set()
-            for s in spec.traverse():
+            for s in spec.traverse(deptype_query=spack.alldeps):
                 package = spack.repo.get(s)
                 if args.missing and package.installed:
                     continue
diff --git a/lib/spack/spack/cmd/info.py b/lib/spack/spack/cmd/info.py
index 64d0d20e24..5774034062 100644
--- a/lib/spack/spack/cmd/info.py
+++ b/lib/spack/spack/cmd/info.py
@@ -81,12 +81,14 @@ def print_text_info(pkg):
 
             print "    " + fmt % (name, default, desc)
 
-    print
-    print "Dependencies:"
-    if pkg.dependencies:
-        colify(pkg.dependencies, indent=4)
-    else:
-        print "    None"
+    for deptype in ('build', 'link', 'run'):
+        print
+        print "%s Dependencies:" % deptype.capitalize()
+        deps = pkg.dependencies(deptype)
+        if deps:
+            colify(deps, indent=4)
+        else:
+            print "    None"
 
     print
     print "Virtual packages: "
diff --git a/lib/spack/spack/cmd/mirror.py b/lib/spack/spack/cmd/mirror.py
index d5f7abe212..0cf682fc4f 100644
--- a/lib/spack/spack/cmd/mirror.py
+++ b/lib/spack/spack/cmd/mirror.py
@@ -179,7 +179,7 @@ def mirror_create(args):
         new_specs = set()
         for spec in specs:
             spec.concretize()
-            for s in spec.traverse():
+            for s in spec.traverse(deptype_query=spack.alldeps):
                 new_specs.add(s)
         specs = list(new_specs)
 
diff --git a/lib/spack/spack/cmd/module.py b/lib/spack/spack/cmd/module.py
index 70da689b67..55826d133c 100644
--- a/lib/spack/spack/cmd/module.py
+++ b/lib/spack/spack/cmd/module.py
@@ -87,7 +87,7 @@ def _find_modules(spec, modules_list):
             return
 
         if flags.recurse_dependencies:
-            for dep in spec.dependencies.values():
+            for dep in spec.dependencies():
                 _find_modules(dep, modules_list)
 
         mod = module_types[mtype](spec)
diff --git a/lib/spack/spack/cmd/package-list.py b/lib/spack/spack/cmd/package-list.py
index 6c5c4ae8c6..bc64c77eab 100644
--- a/lib/spack/spack/cmd/package-list.py
+++ b/lib/spack/spack/cmd/package-list.py
@@ -80,11 +80,15 @@ def print_rst_package_list():
         if pkg.versions:
             print "Versions:"
             print "  " + ", ".join(str(v) for v in reversed(sorted(pkg.versions)))
-        if pkg.dependencies:
-            print "Dependencies"
-            print "  " + ", ".join("`%s`_" % d if d != "mpi" else d
-                                   for d in pkg.dependencies)
-            print
+
+        for deptype in ('build', 'link', 'run'):
+            deps = pkg.dependencies(deptype)
+            if deps:
+                print "%s Dependencies" % deptype.capitalize()
+                print "  " + ", ".join("`%s`_" % d if d != "mpi" else d
+                                       for d in build_deps)
+                print
+
         print "Description:"
         print pkg.format_doc(indent=2)
         print
diff --git a/lib/spack/spack/cmd/test-install.py b/lib/spack/spack/cmd/test-install.py
index 45592a7dda..14c06d136d 100644
--- a/lib/spack/spack/cmd/test-install.py
+++ b/lib/spack/spack/cmd/test-install.py
@@ -133,7 +133,12 @@ def fetch_log(path):
 
 
 def failed_dependencies(spec):
-    return set(item for item in spec.dependencies.itervalues() if not spack.repo.get(item).installed)
+    def get_deps(deptype):
+        return set(item for item in spec.dependencies(deptype)
+                   if not spack.repo.get(item).installed)
+    link_deps = get_deps('link')
+    run_deps = get_deps('run')
+    return link_deps.union(run_deps)
 
 
 def get_top_spec_or_die(args):
diff --git a/lib/spack/spack/concretize.py b/lib/spack/spack/concretize.py
index d9992a5680..386df08b2e 100644
--- a/lib/spack/spack/concretize.py
+++ b/lib/spack/spack/concretize.py
@@ -103,7 +103,7 @@ def cmp_externals(a, b):
         usable.sort(cmp=cmp_externals)
         return usable
 
-
+    # XXX(deptypes): Look here.
     def choose_virtual_or_external(self, spec):
         """Given a list of candidate virtual and external packages, try to
            find one that is most ABI compatible.
@@ -394,8 +394,10 @@ def find_spec(spec, condition):
     """Searches the dag from spec in an intelligent order and looks
        for a spec that matches a condition"""
     # First search parents, then search children
-    dagiter = chain(spec.traverse(direction='parents',  root=False),
-                    spec.traverse(direction='children', root=False))
+    deptype = ('build', 'link')
+    dagiter = chain(
+            spec.traverse(direction='parents',  deptype=deptype, root=False),
+            spec.traverse(direction='children', deptype=deptype, root=False))
     visited = set()
     for relative in dagiter:
         if condition(relative):
@@ -403,7 +405,7 @@ def find_spec(spec, condition):
         visited.add(id(relative))
 
     # Then search all other relatives in the DAG *except* spec
-    for relative in spec.root.traverse():
+    for relative in spec.root.traverse(deptypes=spack.alldeps):
         if relative is spec: continue
         if id(relative) in visited: continue
         if condition(relative):
diff --git a/lib/spack/spack/database.py b/lib/spack/spack/database.py
index a4bbff3d5a..c95abd7423 100644
--- a/lib/spack/spack/database.py
+++ b/lib/spack/spack/database.py
@@ -215,9 +215,14 @@ def _read_spec_from_yaml(self, hash_key, installs, parent_key=None):
         # Add dependencies from other records in the install DB to
         # form a full spec.
         if 'dependencies' in spec_dict[spec.name]:
-            for dep_hash in spec_dict[spec.name]['dependencies'].values():
+            for dep in spec_dict[spec.name]['dependencies'].values():
+                if type(dep) == tuple:
+                    dep_hash, deptypes = dep
+                else:
+                    dep_hash = dep
+                    deptypes = spack.alldeps
                 child = self._read_spec_from_yaml(dep_hash, installs, hash_key)
-                spec._add_dependency(child)
+                spec._add_dependency(child, deptypes)
 
         # Specs from the database need to be marked concrete because
         # they represent actual installations.
@@ -334,7 +339,10 @@ def _check_ref_counts(self):
         counts = {}
         for key, rec in self._data.items():
             counts.setdefault(key, 0)
-            for dep in rec.spec.dependencies.values():
+            # XXX(deptype): This checks all dependencies, but build
+            #               dependencies might be able to be dropped in the
+            #               future.
+            for dep in rec.spec.dependencies():
                 dep_key = dep.dag_hash()
                 counts.setdefault(dep_key, 0)
                 counts[dep_key] += 1
@@ -406,7 +414,7 @@ def _add(self, spec, path, directory_layout=None, explicit=False):
         else:
             self._data[key] = InstallRecord(spec, path, True,
                                             explicit=explicit)
-            for dep in spec.dependencies.values():
+            for dep in spec.dependencies(('link', 'run')):
                 self._increment_ref_count(dep, directory_layout)
 
     def _increment_ref_count(self, spec, directory_layout=None):
@@ -421,7 +429,7 @@ def _increment_ref_count(self, spec, directory_layout=None):
 
             self._data[key] = InstallRecord(spec.copy(), path, installed)
 
-            for dep in spec.dependencies.values():
+            for dep in spec.dependencies('link'):
                 self._increment_ref_count(dep)
 
         self._data[key].ref_count += 1
@@ -466,7 +474,7 @@ def _decrement_ref_count(self, spec):
 
         if rec.ref_count == 0 and not rec.installed:
             del self._data[key]
-            for dep in spec.dependencies.values():
+            for dep in spec.dependencies('link'):
                 self._decrement_ref_count(dep)
 
     def _remove(self, spec):
@@ -480,7 +488,7 @@ def _remove(self, spec):
             return rec.spec
 
         del self._data[key]
-        for dep in rec.spec.dependencies.values():
+        for dep in rec.spec.dependencies('link'):
             self._decrement_ref_count(dep)
 
         # Returns the concrete spec so we know it in the case where a
diff --git a/lib/spack/spack/directives.py b/lib/spack/spack/directives.py
index ca8f21dc08..88d2aaf472 100644
--- a/lib/spack/spack/directives.py
+++ b/lib/spack/spack/directives.py
@@ -171,7 +171,7 @@ def version(pkg, ver, checksum=None, **kwargs):
     pkg.versions[Version(ver)] = kwargs
 
 
-def _depends_on(pkg, spec, when=None):
+def _depends_on(pkg, spec, when=None, type=None):
     # If when is False do nothing
     if when is False:
         return
@@ -180,10 +180,29 @@ def _depends_on(pkg, spec, when=None):
         when = pkg.name
     when_spec = parse_anonymous_spec(when, pkg.name)
 
+    if type is None:
+        # The default deptype is build and link because the common case is to
+        # build against a library which then turns into a runtime dependency
+        # due to the linker.
+        # XXX(deptype): Add 'run' to this? It's an uncommon dependency type,
+        #               but is most backwards-compatible.
+        type = ('build', 'link')
+
+    if isinstance(type, str):
+        type = (type,)
+
+    for deptype in type:
+        if deptype not in spack.spec.alldeps:
+            raise UnknownDependencyTypeError('depends_on', pkg.name, deptype)
+
     dep_spec = Spec(spec)
     if pkg.name == dep_spec.name:
         raise CircularReferenceError('depends_on', pkg.name)
 
+    pkg_deptypes = pkg._deptypes.setdefault(dep_spec.name, set())
+    for deptype in type:
+        pkg_deptypes.add(deptype)
+
     conditions = pkg.dependencies.setdefault(dep_spec.name, {})
     if when_spec in conditions:
         conditions[when_spec].constrain(dep_spec, deps=False)
@@ -191,13 +210,13 @@ def _depends_on(pkg, spec, when=None):
         conditions[when_spec] = dep_spec
 
 
-@directive('dependencies')
-def depends_on(pkg, spec, when=None):
+@directive(('dependencies', '_deptypes'))
+def depends_on(pkg, spec, when=None, type=None):
     """Creates a dict of deps with specs defining when they apply."""
-    _depends_on(pkg, spec, when=when)
+    _depends_on(pkg, spec, when=when, type=type)
 
 
-@directive(('extendees', 'dependencies'))
+@directive(('extendees', 'dependencies', '_deptypes'))
 def extends(pkg, spec, **kwargs):
     """Same as depends_on, but dependency is symlinked into parent prefix.
 
@@ -326,3 +345,13 @@ def __init__(self, directive, package):
             directive,
             "Package '%s' cannot pass itself to %s" % (package, directive))
         self.package = package
+
+
+class UnknownDependencyTypeError(DirectiveError):
+    """This is raised when a dependency is of an unknown type."""
+    def __init__(self, directive, package, deptype):
+        super(UnknownDependencyTypeError, self).__init__(
+            directive,
+            "Package '%s' cannot depend on a package via %s." %
+                (package, deptype))
+        self.package = package
diff --git a/lib/spack/spack/graph.py b/lib/spack/spack/graph.py
index 22058d41d8..063e4647b6 100644
--- a/lib/spack/spack/graph.py
+++ b/lib/spack/spack/graph.py
@@ -80,12 +80,14 @@ def topological_sort(spec, **kwargs):
 
     """
     reverse = kwargs.get('reverse', False)
+    # XXX(deptype): iterate over a certain kind of dependency. Maybe color
+    #               edges based on the type of dependency?
     if not reverse:
-        parents  = lambda s: s.dependents
-        children = lambda s: s.dependencies
+        parents = lambda s: s.dependents()
+        children = lambda s: s.dependencies()
     else:
-        parents  = lambda s: s.dependencies
-        children = lambda s: s.dependents
+        parents = lambda s: s.dependencies()
+        children = lambda s: s.dependents()
 
     # Work on a copy so this is nondestructive.
     spec = spec.copy()
diff --git a/lib/spack/spack/modules.py b/lib/spack/spack/modules.py
index ce46047fa3..a2e528d295 100644
--- a/lib/spack/spack/modules.py
+++ b/lib/spack/spack/modules.py
@@ -120,7 +120,7 @@ def dependencies(spec, request='all'):
         return []
 
     if request == 'direct':
-        return [xx for _, xx in spec.dependencies.items()]
+        return spec.dependencies()
 
     # FIXME : during module file creation nodes seem to be visited multiple
     # FIXME : times even if cover='nodes' is given. This work around permits
diff --git a/lib/spack/spack/package.py b/lib/spack/spack/package.py
index f44b235890..78dfef5829 100644
--- a/lib/spack/spack/package.py
+++ b/lib/spack/spack/package.py
@@ -577,7 +577,7 @@ def extendee_spec(self):
         name = next(iter(self.extendees))
 
         # If the extendee is in the spec's deps already, return that.
-        for dep in self.spec.traverse():
+        for dep in self.spec.traverse(deptypes=('link', 'run')):
             if name == dep.name:
                 return dep
 
@@ -642,7 +642,8 @@ def preorder_traversal(self, visited=None, **kwargs):
             yield self
 
         for name in sorted(self.dependencies.keys()):
-            spec = self.dependencies[name]
+            dep_spec = self.get_dependency(name)
+            spec = dep_spec.spec
 
             # Currently, we do not descend into virtual dependencies, as this
             # makes doing a sensible traversal much harder.  We just assume
@@ -685,7 +686,9 @@ def installed_dependents(self):
         for spec in spack.installed_db.query():
             if self.name == spec.name:
                 continue
-            for dep in spec.traverse():
+            # XXX(deptype): Should build dependencies not count here?
+            #for dep in spec.traverse(deptype=('run')):
+            for dep in spec.traverse(deptype=spack.alldeps):
                 if self.spec == dep:
                     dependents.append(spec)
         return dependents
@@ -1089,7 +1092,7 @@ def check_paths(path_list, filetype, predicate):
 
     def do_install_dependencies(self, **kwargs):
         # Pass along paths of dependencies here
-        for dep in self.spec.dependencies.values():
+        for dep in self.spec.dependencies():
             dep.package.do_install(**kwargs)
 
     @property
@@ -1282,7 +1285,7 @@ def do_activate(self, force=False):
 
         # Activate any package dependencies that are also extensions.
         if not force:
-            for spec in self.spec.traverse(root=False):
+            for spec in self.spec.traverse(root=False, deptype='run'):
                 if spec.package.extends(self.extendee_spec):
                     if not spec.package.activated:
                         spec.package.do_activate(force=force)
@@ -1328,7 +1331,7 @@ def do_deactivate(self, **kwargs):
             for name, aspec in activated.items():
                 if aspec == self.spec:
                     continue
-                for dep in aspec.traverse():
+                for dep in aspec.traverse(deptype='run'):
                     if self.spec == dep:
                         raise ActivationError(
                             "Cannot deactivate %s because %s is activated and depends on it."  # NOQA: ignore=E501
@@ -1414,9 +1417,10 @@ def fetch_remote_versions(self):
     def rpath(self):
         """Get the rpath this package links with, as a list of paths."""
         rpaths = [self.prefix.lib, self.prefix.lib64]
-        rpaths.extend(d.prefix.lib for d in self.spec.traverse(root=False)
+        deps = self.spec.dependencies(deptype='link')
+        rpaths.extend(d.prefix.lib for d in deps
                       if os.path.isdir(d.prefix.lib))
-        rpaths.extend(d.prefix.lib64 for d in self.spec.traverse(root=False)
+        rpaths.extend(d.prefix.lib64 for d in deps
                       if os.path.isdir(d.prefix.lib64))
         return rpaths
 
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index f55dad3c51..58fc139042 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -155,6 +155,9 @@
    every time we call str()"""
 _any_version = VersionList([':'])
 
+alldeps = ('build', 'link', 'run')
+nolink = ('build', 'run')
+
 
 def index_specs(specs):
     """Take a list of specs and return a dict of lists.  Dict is
@@ -291,6 +294,27 @@ def __repr__(self):
         return str(self)
 
 
+@key_ordering
+class DependencySpec(object):
+    """
+    Dependencies have conditions in which they apply.
+
+    This stores both what is depended on and why it is a dependency.
+    """
+    def __init__(self, spec, deptypes):
+        self.spec = spec
+        self.deptypes = deptypes
+
+    def _cmp_key(self):
+        return self.spec
+
+    def copy(self):
+        return DependencySpec(self.spec.copy(), self.deptype)
+
+    def __str__(self):
+        return str(self.spec)
+
+
 @key_ordering
 class VariantSpec(object):
 
@@ -440,11 +464,11 @@ class DependencyMap(HashableMap):
        The DependencyMap is keyed by name. """
     @property
     def concrete(self):
-        return all(d.concrete for d in self.values())
+        return all(d.spec.concrete for d in self.values())
 
     def __str__(self):
         return ''.join(
-            ["^" + str(self[name]) for name in sorted(self.keys())])
+            ["^" + str(self[name].spec) for name in sorted(self.keys())])
 
 
 @key_ordering
@@ -472,13 +496,13 @@ def __init__(self, spec_like, *dep_like, **kwargs):
         # writes directly into this Spec object.
         other = spec_list[0]
         self.name = other.name
-        self.dependents = other.dependents
         self.versions = other.versions
         self.architecture = other.architecture
         self.compiler = other.compiler
         self.compiler_flags = other.compiler_flags
         self.compiler_flags.spec = self
-        self.dependencies = other.dependencies
+        self._dependencies = other._dependencies
+        self._dependents = other._dependents
         self.variants = other.variants
         self.variants.spec = self
         self.namespace = other.namespace
@@ -500,7 +524,49 @@ def __init__(self, spec_like, *dep_like, **kwargs):
         # Spec(a, b) will copy a but just add b as a dep.
         for dep in dep_like:
             spec = dep if isinstance(dep, Spec) else Spec(dep)
-            self._add_dependency(spec)
+            # XXX(deptype): default deptypes
+            self._add_dependency(spec, ('build', 'link'))
+
+    def get_dependency(self, name):
+        dep = self._dependencies.get(name)
+        if dep is not None:
+            return dep
+        raise InvalidDependencyException(
+            self.name + " does not depend on " + comma_or(name))
+
+    def _deptype_norm(self, deptype):
+        if deptype is None:
+            return alldeps
+        # Force deptype to be a set object so that we can do set intersections.
+        if isinstance(deptype, str):
+            return (deptype,)
+        return deptype
+
+    def _find_deps(self, where, deptype):
+        deptype = self._deptype_norm(deptype)
+
+        return [dep.spec
+                for dep in where.values()
+                if deptype and any(d in deptype for d in dep.deptypes)]
+
+    def dependencies(self, deptype=None):
+        return self._find_deps(self._dependencies, deptype)
+
+    def dependents(self, deptype=None):
+        return self._find_deps(self._dependents, deptype)
+
+    def _find_deps_dict(self, where, deptype):
+        deptype = self._deptype_norm(deptype)
+
+        return [(dep.spec.name, dep)
+                for dep in where.values()
+                if deptype and any(d in deptype for d in dep.deptypes)]
+
+    def dependencies_dict(self, deptype=None):
+        return dict(self._find_deps_dict(self._dependencies, deptype))
+
+    def dependents_dict(self, deptype=None):
+        return dict(self._find_deps_dict(self._dependents, deptype))
 
     #
     # Private routines here are called by the parser when building a spec.
@@ -609,13 +675,13 @@ def _set_target(self, value):
         if self.architecture.platform:
             self.architecture.target = self.architecture.platform.target(value)
 
-    def _add_dependency(self, spec):
+    def _add_dependency(self, spec, deptypes):
         """Called by the parser to add another spec as a dependency."""
-        if spec.name in self.dependencies:
+        if spec.name in self._dependencies:
             raise DuplicateDependencyError(
                 "Cannot depend on '%s' twice" % spec)
-        self.dependencies[spec.name] = spec
-        spec.dependents[self.name] = self
+        self._dependencies[spec.name] = DependencySpec(spec, deptypes)
+        spec._dependents[self.name] = DependencySpec(self, deptypes)
 
     #
     # Public interface
@@ -632,15 +698,15 @@ def root(self):
            installed).  This will throw an assertion error if that is not
            the case.
         """
-        if not self.dependents:
+        if not self._dependents:
             return self
 
         # If the spec has multiple dependents, ensure that they all
         # lead to the same place.  Spack shouldn't deal with any DAGs
         # with multiple roots, so something's wrong if we find one.
-        depiter = iter(self.dependents.values())
-        first_root = next(depiter).root
-        assert(all(first_root is d.root for d in depiter))
+        depiter = iter(self._dependents.values())
+        first_root = next(depiter).spec.root
+        assert(all(first_root is d.spec.root for d in depiter))
         return first_root
 
     @property
@@ -687,10 +753,21 @@ def concrete(self):
                               and self.architecture.concrete
                               and self.compiler and self.compiler.concrete
                               and self.compiler_flags.concrete
-                              and self.dependencies.concrete)
+                              and self._dependencies.concrete)
         return self._concrete
 
-    def traverse(self, visited=None, d=0, **kwargs):
+    def traverse(self, visited=None, deptype=None, **kwargs):
+        traversal = self.traverse_with_deptype(visited=visited,
+                                               deptype=deptype,
+                                               **kwargs)
+        if kwargs.get('depth', False):
+            return [(s[0], s[1].spec) for s in traversal]
+        else:
+            return [s.spec for s in traversal]
+
+    def traverse_with_deptype(self, visited=None, d=0, deptype=None,
+                              deptype_query=None, _self_deptype=None,
+                              **kwargs):
         """Generic traversal of the DAG represented by this spec.
            This will yield each node in the spec.  Options:
 
@@ -742,6 +819,12 @@ def traverse(self, visited=None, d=0, **kwargs):
         direction = kwargs.get('direction', 'children')
         order = kwargs.get('order', 'pre')
 
+        if deptype is None:
+            deptype = alldeps
+
+        if deptype_query is None:
+            deptype_query = ('link', 'run')
+
         # Make sure kwargs have legal values; raise ValueError if not.
         def validate(name, val, allowed_values):
             if val not in allowed_values:
@@ -759,30 +842,37 @@ def validate(name, val, allowed_values):
         if key in visited and cover == 'nodes':
             return
 
-        # Determine whether and what to yield for this node.
+        def return_val(res):
+            return (d, res) if depth else res
+
         yield_me = yield_root or d > 0
-        result = (d, self) if depth else self
 
         # Preorder traversal yields before successors
         if yield_me and order == 'pre':
-            yield result
+            yield return_val(DependencySpec(self, _self_deptype))
+
+        deps = self.dependencies_dict(deptype)
 
         # Edge traversal yields but skips children of visited nodes
         if not (key in visited and cover == 'edges'):
             # This code determines direction and yields the children/parents
-            successors = self.dependencies
+            successors = deps
             if direction == 'parents':
-                successors = self.dependents
+                successors = self.dependents_dict()
 
             visited.add(key)
             for name in sorted(successors):
                 child = successors[name]
-                for elt in child.traverse(visited, d + 1, **kwargs):
+                children = child.spec.traverse_with_deptype(
+                        visited, d=d + 1, deptype=deptype_query,
+                        deptype_query=deptype_query,
+                        _self_deptype=child.deptypes, **kwargs)
+                for elt in children:
                     yield elt
 
         # Postorder traversal yields after successors
         if yield_me and order == 'post':
-            yield result
+            yield return_val(DependencySpec(self, _self_deptype))
 
     @property
     def short_spec(self):
@@ -807,6 +897,7 @@ def dag_hash(self, length=None):
         if self._hash:
             return self._hash[:length]
         else:
+            # XXX(deptype): ignore 'build' dependencies here
             yaml_text = yaml.dump(
                 self.to_node_dict(), default_flow_style=True, width=sys.maxint)
             sha = hashlib.sha1(yaml_text)
@@ -819,11 +910,13 @@ def to_node_dict(self):
         params = dict((name, v.value) for name, v in self.variants.items())
         params.update(dict((name, value)
                       for name, value in self.compiler_flags.items()))
+        deps = self.dependencies_dict(deptype=('link', 'run'))
         d = {
-            'parameters' : params,
-            'arch' : self.architecture,
-            'dependencies' : dict((d, self.dependencies[d].dag_hash())
-                                  for d in sorted(self.dependencies))
+            'parameters': params,
+            'arch': self.architecture,
+            'dependencies': dict((d, (deps[d].spec.dag_hash(),
+                                      deps[d].deptypes))
+                                 for d in sorted(deps.keys()))
         }
 
         # Older concrete specs do not have a namespace.  Omit for
@@ -848,7 +941,7 @@ def to_node_dict(self):
 
     def to_yaml(self, stream=None):
         node_list = []
-        for s in self.traverse(order='pre'):
+        for s in self.traverse(order='pre', deptype=('link', 'run')):
             node = s.to_node_dict()
             node[s.name]['hash'] = s.dag_hash()
             node_list.append(node)
@@ -889,6 +982,11 @@ def from_node_dict(node):
             raise SpackRecordError(
                 "Did not find a valid format for variants in YAML file")
 
+        # XXX(deptypes): why are dependencies not meant to be read here?
+        #for name, dep_info in node['dependencies'].items():
+        #    (dag_hash, deptypes) = dep_info
+        #    spec._dependencies[name] = DependencySpec(dag_hash, deptypes)
+
         return spec
 
     @staticmethod
@@ -919,8 +1017,10 @@ def from_yaml(stream):
 
         for node in yfile['spec']:
             name = next(iter(node))
-            for dep_name in node[name]['dependencies']:
-                deps[name].dependencies[dep_name] = deps[dep_name]
+            for dep_name, (dep, deptypes) in \
+                    node[name]['dependencies'].items():
+                deps[name]._dependencies[dep_name] = \
+                        DependencySpec(deps[dep_name], deptypes)
         return spec
 
     def _concretize_helper(self, presets=None, visited=None):
@@ -940,8 +1040,9 @@ def _concretize_helper(self, presets=None, visited=None):
         changed = False
 
         # Concretize deps first -- this is a bottom-up process.
-        for name in sorted(self.dependencies.keys()):
-            changed |= self.dependencies[name]._concretize_helper(presets, visited)
+        for name in sorted(self._dependencies.keys()):
+            changed |= self._dependencies[
+                name].spec._concretize_helper(presets, visited)
 
         if self.name in presets:
             changed |= self.constrain(presets[self.name])
@@ -965,13 +1066,16 @@ def _concretize_helper(self, presets=None, visited=None):
     def _replace_with(self, concrete):
         """Replace this virtual spec with a concrete spec."""
         assert(self.virtual)
-        for name, dependent in self.dependents.items():
+        for name, dep_spec in self._dependents.items():
+            dependent = dep_spec.spec
+            deptypes = dep_spec.deptypes
+
             # remove self from all dependents.
-            del dependent.dependencies[self.name]
+            del dependent._dependencies[self.name]
 
             # add the replacement, unless it is already a dep of dependent.
-            if concrete.name not in dependent.dependencies:
-                dependent._add_dependency(concrete)
+            if concrete.name not in dependent._dependencies:
+                dependent._add_dependency(concrete, deptypes)
 
     def _replace_node(self, replacement):
         """Replace this spec with another.
@@ -982,13 +1086,15 @@ def _replace_node(self, replacement):
         to be normalized.
 
         """
-        for name, dependent in self.dependents.items():
-            del dependent.dependencies[self.name]
-            dependent._add_dependency(replacement)
+        for name, dep_spec in self._dependents.items():
+            dependent = dep_spec.spec
+            deptypes = dep_spec.deptypes
+            del dependent._dependencies[self.name]
+            dependent._add_dependency(replacement, deptypes)
 
-        for name, dep in self.dependencies.items():
-            del dep.dependents[self.name]
-            del self.dependencies[dep.name]
+        for name, dep_spec in self._dependencies.items():
+            del dep_spec.spec.dependents[self.name]
+            del self._dependencies[dep.name]
 
     def _expand_virtual_packages(self):
         """Find virtual packages in this spec, replace them with providers,
@@ -1008,13 +1114,14 @@ def _expand_virtual_packages(self):
               a problem.
         """
         # Make an index of stuff this spec already provides
+        # XXX(deptype): 'link' and 'run'?
         self_index = ProviderIndex(self.traverse(), restrict=True)
         changed = False
         done = False
 
         while not done:
             done = True
-
+            # XXX(deptype): 'link' and 'run'?
             for spec in list(self.traverse()):
                 replacement = None
                 if spec.virtual:
@@ -1054,10 +1161,10 @@ def _expand_virtual_packages(self):
 
                 # If replacement is external then trim the dependencies
                 if replacement.external or replacement.external_module:
-                    if (spec.dependencies):
+                    if (spec._dependencies):
                         changed = True
-                        spec.dependencies = DependencyMap()
-                    replacement.dependencies = DependencyMap()
+                        spec._dependencies = DependencyMap()
+                    replacement._dependencies = DependencyMap()
                     replacement.architecture = self.architecture
 
                 # TODO: could this and the stuff in _dup be cleaned up?
@@ -1068,7 +1175,7 @@ def feq(cfield, sfield):
                     feq(replacement.versions, spec.versions) and
                     feq(replacement.compiler, spec.compiler) and
                     feq(replacement.architecture, spec.architecture) and
-                    feq(replacement.dependencies, spec.dependencies) and
+                    feq(replacement._dependencies, spec._dependencies) and
                     feq(replacement.variants, spec.variants) and
                     feq(replacement.external, spec.external) and
                     feq(replacement.external_module, spec.external_module)):
@@ -1146,7 +1253,7 @@ def _mark_concrete(self):
         Only for internal use -- client code should use "concretize"
         unless there is a need to force a spec to be concrete.
         """
-        for s in self.traverse():
+        for s in self.traverse(deptype_query=alldeps):
             s._normal = True
             s._concrete = True
 
@@ -1159,6 +1266,13 @@ def concretized(self):
         return clone
 
     def flat_dependencies(self, **kwargs):
+        flat_deps = DependencyMap()
+        flat_deps_deptypes = self.flat_dependencies_with_deptype(**kwargs)
+        for name, depspec in flat_deps_deptypes.items():
+            flat_deps[name] = depspec.spec
+        return flat_deps
+
+    def flat_dependencies_with_deptype(self, **kwargs):
         """Return a DependencyMap containing all of this spec's
            dependencies with their constraints merged.
 
@@ -1169,23 +1283,31 @@ def flat_dependencies(self, **kwargs):
            returns them.
         """
         copy = kwargs.get('copy', True)
+        deptype_query = kwargs.get('deptype_query')
 
         flat_deps = DependencyMap()
         try:
-            for spec in self.traverse(root=False):
+            deptree = self.traverse_with_deptype(root=False,
+                                                 deptype_query=deptype_query)
+            for depspec in deptree:
+                spec = depspec.spec
+                deptypes = depspec.deptypes
+
                 if spec.name not in flat_deps:
                     if copy:
-                        flat_deps[spec.name] = spec.copy(deps=False)
+                        dep_spec = DependencySpec(spec.copy(deps=False),
+                                                  deptypes)
                     else:
-                        flat_deps[spec.name] = spec
+                        dep_spec = DependencySpec(spec, deptypes)
+                    flat_deps[spec.name] = dep_spec
                 else:
-                    flat_deps[spec.name].constrain(spec)
+                    flat_deps[spec.name].spec.constrain(spec)
 
             if not copy:
-                for dep in flat_deps.values():
-                    dep.dependencies.clear()
-                    dep.dependents.clear()
-                self.dependencies.clear()
+                for depspec in flat_deps.values():
+                    depspec.spec._dependencies.clear()
+                    depspec.spec._dependents.clear()
+                self._dependencies.clear()
 
             return flat_deps
 
@@ -1200,17 +1322,11 @@ def index(self):
         """Return DependencyMap that points to all the dependencies in this
            spec."""
         dm = DependencyMap()
+        # XXX(deptype): use a deptype kwarg.
         for spec in self.traverse():
             dm[spec.name] = spec
         return dm
 
-    def flatten(self):
-        """Pull all dependencies up to the root (this spec).
-           Merge constraints for dependencies with the same name, and if they
-           conflict, throw an exception. """
-        for dep in self.flat_dependencies(copy=False):
-            self._add_dependency(dep)
-
     def _evaluate_dependency_conditions(self, name):
         """Evaluate all the conditions on a dependency with this name.
 
@@ -1267,7 +1383,8 @@ def _find_provider(self, vdep, provider_index):
             elif required:
                 raise UnsatisfiableProviderSpecError(required[0], vdep)
 
-    def _merge_dependency(self, dep, visited, spec_deps, provider_index):
+    def _merge_dependency(self, dep, deptypes, visited, spec_deps,
+                          provider_index):
         """Merge the dependency into this spec.
 
         This is the core of normalize().  There are some basic steps:
@@ -1294,7 +1411,9 @@ def _merge_dependency(self, dep, visited, spec_deps, provider_index):
                 dep = provider
         else:
             index = ProviderIndex([dep], restrict=True)
-            for vspec in (v for v in spec_deps.values() if v.virtual):
+            for vspec in (v.spec
+                          for v in spec_deps.values()
+                          if v.spec.virtual):
                 if index.providers_for(vspec):
                     vspec._replace_with(dep)
                     del spec_deps[vspec.name]
@@ -1307,25 +1426,25 @@ def _merge_dependency(self, dep, visited, spec_deps, provider_index):
         # If the spec isn't already in the set of dependencies, clone
         # it from the package description.
         if dep.name not in spec_deps:
-            spec_deps[dep.name] = dep.copy()
+            spec_deps[dep.name] = DependencySpec(dep.copy(), deptypes)
             changed = True
         # Constrain package information with spec info
         try:
-            changed |= spec_deps[dep.name].constrain(dep)
+            changed |= spec_deps[dep.name].spec.constrain(dep)
 
         except UnsatisfiableSpecError, e:
             e.message = "Invalid spec: '%s'. "
             e.message += "Package %s requires %s %s, but spec asked for %s"
-            e.message %= (spec_deps[dep.name], dep.name, e.constraint_type,
-                          e.required, e.provided)
+            e.message %= (spec_deps[dep.name].spec, dep.name,
+                          e.constraint_type, e.required, e.provided)
             raise e
 
         # Add merged spec to my deps and recurse
         dependency = spec_deps[dep.name]
-        if dep.name not in self.dependencies:
-            self._add_dependency(dependency)
+        if dep.name not in self._dependencies:
+            self._add_dependency(dependency.spec, dependency.deptypes)
 
-        changed |= dependency._normalize_helper(
+        changed |= dependency.spec._normalize_helper(
             visited, spec_deps, provider_index)
         return changed
 
@@ -1351,10 +1470,11 @@ def _normalize_helper(self, visited, spec_deps, provider_index):
             for dep_name in pkg.dependencies:
                 # Do we depend on dep_name?  If so pkg_dep is not None.
                 pkg_dep = self._evaluate_dependency_conditions(dep_name)
+                deptypes = pkg._deptypes[dep_name]
                 # If pkg_dep is a dependency, merge it.
                 if pkg_dep:
                     changed |= self._merge_dependency(
-                        pkg_dep, visited, spec_deps, provider_index)
+                        pkg_dep, deptypes, visited, spec_deps, provider_index)
             any_change |= changed
 
         return any_change
@@ -1385,11 +1505,13 @@ def normalize(self, force=False):
         # Ensure first that all packages & compilers in the DAG exist.
         self.validate_names()
         # Get all the dependencies into one DependencyMap
-        spec_deps = self.flat_dependencies(copy=False)
+        spec_deps = self.flat_dependencies_with_deptype(copy=False,
+                                                        deptype_query=alldeps)
 
         # Initialize index of virtual dependency providers if
         # concretize didn't pass us one already
-        provider_index = ProviderIndex(spec_deps.values(), restrict=True)
+        provider_index = ProviderIndex([s.spec for s in spec_deps.values()],
+                                       restrict=True)
 
         # traverse the package DAG and fill out dependencies according
         # to package files & their 'when' specs
@@ -1510,7 +1632,7 @@ def _constrain_dependencies(self, other):
         """Apply constraints of other spec's dependencies to this spec."""
         other = self._autospec(other)
 
-        if not self.dependencies or not other.dependencies:
+        if not self._dependencies or not other._dependencies:
             return False
 
         # TODO: might want more detail than this, e.g. specific deps
@@ -1526,13 +1648,17 @@ def _constrain_dependencies(self, other):
 
         # Update with additional constraints from other spec
         for name in other.dep_difference(self):
-            self._add_dependency(other[name].copy())
+            dep_spec_copy = other.get_dependency(name)
+            dep_copy = dep_spec_copy.spec
+            deptypes = dep_spec_copy.deptypes
+            self._add_dependency(dep_copy.copy(), deptypes)
             changed = True
 
         return changed
 
     def common_dependencies(self, other):
         """Return names of dependencies that self an other have in common."""
+        # XXX(deptype): handle deptypes via deptype kwarg.
         common = set(
             s.name for s in self.traverse(root=False))
         common.intersection_update(
@@ -1657,13 +1783,14 @@ def satisfies_dependencies(self, other, strict=False):
         other = self._autospec(other)
 
         if strict:
-            if other.dependencies and not self.dependencies:
+            if other._dependencies and not self._dependencies:
                 return False
 
-            if not all(dep in self.dependencies for dep in other.dependencies):
+            if not all(dep in self._dependencies
+                       for dep in other._dependencies):
                 return False
 
-        elif not self.dependencies or not other.dependencies:
+        elif not self._dependencies or not other._dependencies:
             # if either spec doesn't restrict dependencies then both are
             # compatible.
             return True
@@ -1726,8 +1853,8 @@ def _dup(self, other, **kwargs):
         self.architecture = other.architecture
         self.compiler = other.compiler.copy() if other.compiler else None
         if kwargs.get('cleardeps', True):
-            self.dependents = DependencyMap()
-            self.dependencies = DependencyMap()
+            self._dependents = DependencyMap()
+            self._dependencies = DependencyMap()
         self.compiler_flags = other.compiler_flags.copy()
         self.variants = other.variants.copy()
         self.variants.spec = self
@@ -1739,15 +1866,30 @@ def _dup(self, other, **kwargs):
         # If we copy dependencies, preserve DAG structure in the new spec
         if kwargs.get('deps', True):
             # This copies the deps from other using _dup(deps=False)
-            new_nodes = other.flat_dependencies()
+            # XXX(deptype): We can keep different instances of specs here iff
+            #               it is only a 'build' dependency (from its parent).
+            #               All other instances must be shared (due to symbol
+            #               and PATH contention). These should probably search
+            #               for any existing installation which can satisfy the
+            #               build and latch onto that because if 3 things need
+            #               the same build dependency and it is *not*
+            #               available, we only want to build it once.
+            new_nodes = other.flat_dependencies(deptype_query=alldeps)
             new_nodes[self.name] = self
 
-            # Hook everything up properly here by traversing.
-            for spec in other.traverse(cover='nodes'):
-                parent = new_nodes[spec.name]
-                for child in spec.dependencies:
-                    if child not in parent.dependencies:
-                        parent._add_dependency(new_nodes[child])
+            stack = [other]
+            while stack:
+                cur_spec = stack.pop(0)
+                new_spec = new_nodes[cur_spec.name]
+
+                for depspec in cur_spec._dependencies.values():
+                    stack.append(depspec.spec)
+
+                    # XXX(deptype): add any new deptypes that may have appeared
+                    #               here.
+                    if depspec.spec.name not in new_spec._dependencies:
+                        new_spec._add_dependency(
+                                new_nodes[depspec.spec.name], depspec.deptypes)
 
         # Since we preserved structure, we can copy _normal safely.
         self._normal = other._normal
@@ -1814,13 +1956,13 @@ def _eq_dag(self, other, vs, vo):
         if self.ne_node(other):
             return False
 
-        if len(self.dependencies) != len(other.dependencies):
+        if len(self._dependencies) != len(other._dependencies):
             return False
 
-        ssorted = [self.dependencies[name]
-                   for name in sorted(self.dependencies)]
-        osorted = [other.dependencies[name]
-                   for name in sorted(other.dependencies)]
+        ssorted = [self._dependencies[name].spec
+                   for name in sorted(self._dependencies)]
+        osorted = [other._dependencies[name].spec
+                   for name in sorted(other._dependencies)]
 
         for s, o in zip(ssorted, osorted):
             visited_s = id(s) in vs
@@ -1874,9 +2016,10 @@ def _cmp_key(self):
           1. A tuple describing this node in the DAG.
           2. The hash of each of this node's dependencies' cmp_keys.
         """
+        dep_dict = self.dependencies_dict(deptype=('link', 'run'))
         return self._cmp_node() + (
-            tuple(hash(self.dependencies[name])
-                  for name in sorted(self.dependencies)),)
+            tuple(hash(dep_dict[name])
+                  for name in sorted(dep_dict)),)
 
     def colorized(self):
         return colorize_spec(self)
@@ -2081,8 +2224,8 @@ def __cmp__(self, other):
                          self.architecture, other.architecture)
 
         #Dependency is not configurable
-        if self.dependencies != other.dependencies:
-            return -1 if self.dependencies < other.dependencies else 1
+        if self._dependencies != other._dependencies:
+            return -1 if self._dependencies < other._dependencies else 1
 
         #Equal specs
         return 0
@@ -2196,10 +2339,13 @@ def do_parse(self):
                         specs.append(self.spec(None))
                         self.previous = None
                     if self.accept(HASH):
-                        specs[-1]._add_dependency(self.spec_by_hash())
+                        dep = self.spec_by_hash()
                     else:
                         self.expect(ID)
-                        specs[-1]._add_dependency(self.spec(self.token.value))
+                        dep = self.spec(self.token.value)
+                    # XXX(deptype): default deptypes
+                    def_deptypes = ('build', 'link')
+                    specs[-1]._add_dependency(dep, def_deptypes)
 
                 else:
                     # Attempt to construct an anonymous spec, but check that
@@ -2263,8 +2409,8 @@ def spec(self, name, check_valid_token=False):
         spec.external = None
         spec.external_module = None
         spec.compiler_flags = FlagMap(spec)
-        spec.dependents = DependencyMap()
-        spec.dependencies = DependencyMap()
+        spec._dependents = DependencyMap()
+        spec._dependencies = DependencyMap()
         spec.namespace = spec_namespace
         spec._hash = None
 
diff --git a/lib/spack/spack/test/cmd/test_install.py b/lib/spack/spack/test/cmd/test_install.py
index d17e013ed2..a94d3c8bba 100644
--- a/lib/spack/spack/test/cmd/test_install.py
+++ b/lib/spack/spack/test/cmd/test_install.py
@@ -58,16 +58,39 @@ def mock_open(filename, mode):
 
 class MockSpec(object):
     def __init__(self, name, version, hashStr=None):
-        self.dependencies = {}
+        self._dependencies = {}
         self.name = name
         self.version = version
         self.hash = hashStr if hashStr else hash((name, version))
 
+    def _deptype_norm(self, deptype):
+        if deptype is None:
+            return spack.alldeps
+        # Force deptype to be a tuple so that we can do set intersections.
+        if isinstance(deptype, str):
+            return (deptype,)
+        return deptype
+
+    def _find_deps(self, where, deptype):
+        deptype = self._deptype_norm(deptype)
+
+        return [dep.spec
+                for dep in where.values()
+                if deptype and any(d in deptype for d in dep.deptypes)]
+
+    def dependencies(self, deptype=None):
+        return self._find_deps(self._dependencies, deptype)
+
+    def dependents(self, deptype=None):
+        return self._find_deps(self._dependents, deptype)
+
     def traverse(self, order=None):
-        for _, spec in self.dependencies.items():
-            yield spec
+        for _, spec in self._dependencies.items():
+            yield spec.spec
         yield self
-        #allDeps = itertools.chain.from_iterable(i.traverse() for i in self.dependencies.itervalues())
+        #from_iterable = itertools.chain.from_iterable
+        #allDeps = from_iterable(i.traverse()
+        #                        for i in self.dependencies())
         #return set(itertools.chain([self], allDeps))
 
     def dag_hash(self):
@@ -104,7 +127,7 @@ def mock_fetch_log(path):
 
 specX = MockSpec('X', "1.2.0")
 specY = MockSpec('Y', "2.3.8")
-specX.dependencies['Y'] = specY
+specX._dependencies['Y'] = spack.DependencySpec(specY, spack.alldeps)
 pkgX = MockPackage(specX, 'logX')
 pkgY = MockPackage(specY, 'logY')
 
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index ce02b08bc3..ae3ceecfc8 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -197,32 +197,36 @@ def test_concretize_two_virtuals_with_dual_provider_and_a_conflict(self):
     def test_virtual_is_fully_expanded_for_callpath(self):
         # force dependence on fake "zmpi" by asking for MPI 10.0
         spec = Spec('callpath ^mpi@10.0')
-        self.assertTrue('mpi' in spec.dependencies)
+        self.assertTrue('mpi' in spec._dependencies)
         self.assertFalse('fake' in spec)
 
         spec.concretize()
 
-        self.assertTrue('zmpi' in spec.dependencies)
-        self.assertTrue(all(not 'mpi' in d.dependencies for d in spec.traverse()))
+        self.assertTrue('zmpi' in spec._dependencies)
+        self.assertTrue(all('mpi' not in d._dependencies
+                            for d in spec.traverse()))
         self.assertTrue('zmpi' in spec)
         self.assertTrue('mpi' in spec)
 
-        self.assertTrue('fake' in spec.dependencies['zmpi'])
+        self.assertTrue('fake' in spec._dependencies['zmpi'].spec)
 
 
     def test_virtual_is_fully_expanded_for_mpileaks(self):
         spec = Spec('mpileaks ^mpi@10.0')
-        self.assertTrue('mpi' in spec.dependencies)
+        self.assertTrue('mpi' in spec._dependencies)
         self.assertFalse('fake' in spec)
 
         spec.concretize()
 
-        self.assertTrue('zmpi' in spec.dependencies)
-        self.assertTrue('callpath' in spec.dependencies)
-        self.assertTrue('zmpi' in spec.dependencies['callpath'].dependencies)
-        self.assertTrue('fake' in spec.dependencies['callpath'].dependencies['zmpi'].dependencies)
+        self.assertTrue('zmpi' in spec._dependencies)
+        self.assertTrue('callpath' in spec._dependencies)
+        self.assertTrue('zmpi' in spec._dependencies['callpath'].
+                                  spec._dependencies)
+        self.assertTrue('fake' in spec._dependencies['callpath'].
+                                  spec._dependencies['zmpi'].
+                                  spec._dependencies)
 
-        self.assertTrue(all(not 'mpi' in d.dependencies for d in spec.traverse()))
+        self.assertTrue(all(not 'mpi' in d._dependencies for d in spec.traverse()))
         self.assertTrue('zmpi' in spec)
         self.assertTrue('mpi' in spec)
 
diff --git a/lib/spack/spack/test/mock_packages_test.py b/lib/spack/spack/test/mock_packages_test.py
index c8b06cd7d7..9d96622a6e 100644
--- a/lib/spack/spack/test/mock_packages_test.py
+++ b/lib/spack/spack/test/mock_packages_test.py
@@ -191,8 +191,7 @@ def initmock(self):
         # restore later.
         self.saved_deps = {}
 
-
-    def set_pkg_dep(self, pkg_name, spec):
+    def set_pkg_dep(self, pkg_name, spec, deptypes=spack.alldeps):
         """Alters dependence information for a package.
 
         Adds a dependency on <spec> to pkg.
@@ -206,7 +205,9 @@ def set_pkg_dep(self, pkg_name, spec):
             self.saved_deps[pkg_name] = (pkg, pkg.dependencies.copy())
 
         # Change dep spec
-        pkg.dependencies[spec.name] = { Spec(pkg_name) : spec }
+        # XXX(deptype): handle deptypes.
+        pkg.dependencies[spec.name] = {Spec(pkg_name): spec}
+        pkg._deptypes[spec.name] = set(deptypes)
 
 
     def cleanmock(self):
@@ -216,6 +217,7 @@ def cleanmock(self):
         shutil.rmtree(self.temp_config, ignore_errors=True)
         spack.config.clear_config_caches()
 
+        # XXX(deptype): handle deptypes.
         # Restore dependency changes that happened during the test
         for pkg_name, (pkg, deps) in self.saved_deps.items():
             pkg.dependencies.clear()
diff --git a/lib/spack/spack/test/spec_dag.py b/lib/spack/spack/test/spec_dag.py
index c56c70b1fe..972e79aa20 100644
--- a/lib/spack/spack/test/spec_dag.py
+++ b/lib/spack/spack/test/spec_dag.py
@@ -148,10 +148,12 @@ def test_conflicting_spec_constraints(self):
         # Normalize then add conflicting constraints to the DAG (this is an
         # extremely unlikely scenario, but we test for it anyway)
         mpileaks.normalize()
-        mpileaks.dependencies['mpich'] = Spec('mpich@1.0')
-        mpileaks.dependencies['callpath'].dependencies['mpich'] = Spec('mpich@2.0')
+        mpileaks._dependencies['mpich'].spec = Spec('mpich@1.0')
+        mpileaks._dependencies['callpath']. \
+            spec._dependencies['mpich'].spec = Spec('mpich@2.0')
 
-        self.assertRaises(spack.spec.InconsistentSpecError, mpileaks.flatten)
+        self.assertRaises(spack.spec.InconsistentSpecError,
+                lambda: mpileaks.flat_dependencies(copy=False))
 
 
     def test_normalize_twice(self):
@@ -197,15 +199,17 @@ def test_normalize_with_virtual_spec(self):
 
     def check_links(self, spec_to_check):
         for spec in spec_to_check.traverse():
-            for dependent in spec.dependents.values():
+            for dependent in spec.dependents():
                 self.assertTrue(
-                    spec.name in dependent.dependencies,
-                    "%s not in dependencies of %s" % (spec.name, dependent.name))
+                    spec.name in dependent.dependencies_dict(),
+                    "%s not in dependencies of %s" %
+                        (spec.name, dependent.name))
 
-            for dependency in spec.dependencies.values():
+            for dependency in spec.dependencies():
                 self.assertTrue(
-                    spec.name in dependency.dependents,
-                    "%s not in dependents of %s" % (spec.name, dependency.name))
+                    spec.name in dependency.dependents_dict(),
+                    "%s not in dependents of %s" %
+                        (spec.name, dependency.name))
 
 
     def test_dependents_and_dependencies_are_correct(self):
@@ -442,3 +446,69 @@ def test_copy_concretized(self):
         orig_ids = set(id(s) for s in orig.traverse())
         copy_ids = set(id(s) for s in copy.traverse())
         self.assertFalse(orig_ids.intersection(copy_ids))
+
+    """
+    Here is the graph with deptypes labeled (assume all packages have a 'dt'
+    prefix). Arrows are marked with the deptypes ('b' for 'build', 'l' for
+    'link', 'r' for 'run').
+
+        use -bl-> top
+
+        top -b->  build1
+        top -bl-> link1
+        top -r->  run1
+
+        build1 -b->  build2
+        build1 -bl-> link2
+        build1 -r->  run2
+
+        link1 -bl-> link3
+
+        run1 -bl-> link5
+        run1 -r->  run3
+
+        link3 -b->  build2
+        link3 -bl-> link4
+
+        run3 -b-> build3
+    """
+    def test_deptype_traversal(self):
+        dag = Spec('dtuse')
+        dag.normalize()
+
+        names = ['dtuse', 'dttop', 'dtlink1', 'dtlink3', 'dtlink4',
+                 'dtrun1', 'dtlink5', 'dtrun3']
+
+        traversal = dag.traverse()
+        self.assertEqual([x.name for x in traversal], names)
+
+    def test_deptype_traversal_with_builddeps(self):
+        dag = Spec('dttop')
+        dag.normalize()
+
+        names = ['dttop', 'dtbuild1', 'dtlink2', 'dtrun2', 'dtlink1',
+                 'dtlink3', 'dtlink4', 'dtrun1', 'dtlink5', 'dtrun3']
+
+        traversal = dag.traverse()
+        self.assertEqual([x.name for x in traversal], names)
+
+    def test_deptype_traversal_full(self):
+        dag = Spec('dttop')
+        dag.normalize()
+
+        names = ['dttop', 'dtbuild1', 'dtbuild2', 'dtlink2', 'dtrun2',
+                 'dtlink1', 'dtlink3', 'dtlink4', 'dtrun1', 'dtlink5',
+                 'dtrun3', 'dtbuild3']
+
+        traversal = dag.traverse(deptype_query=spack.alldeps)
+        self.assertEqual([x.name for x in traversal], names)
+
+    def test_deptype_traversal_pythonpath(self):
+        dag = Spec('dttop')
+        dag.normalize()
+
+        names = ['dttop', 'dtbuild1', 'dtrun2', 'dtlink1', 'dtrun1',
+                 'dtrun3']
+
+        traversal = dag.traverse(deptype=spack.nolink, deptype_query='run')
+        self.assertEqual([x.name for x in traversal], names)
diff --git a/var/spack/repos/builtin.mock/packages/cmake-client/package.py b/var/spack/repos/builtin.mock/packages/cmake-client/package.py
index 355689a2d2..c58430317a 100644
--- a/var/spack/repos/builtin.mock/packages/cmake-client/package.py
+++ b/var/spack/repos/builtin.mock/packages/cmake-client/package.py
@@ -38,7 +38,7 @@ class CmakeClient(Package):
 
     version('1.0', '4cb3ff35b2472aae70f542116d616e63')
 
-    depends_on('cmake')
+    depends_on('cmake', type='build')
 
 
     def setup_environment(self, spack_env, run_env):
diff --git a/var/spack/repos/builtin.mock/packages/dtbuild1/package.py b/var/spack/repos/builtin.mock/packages/dtbuild1/package.py
new file mode 100644
index 0000000000..7429b2a8ef
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtbuild1/package.py
@@ -0,0 +1,18 @@
+from spack import *
+
+
+class Dtbuild1(Package):
+    """Package for use as a build tool for deptypes testing which has its own
+    deptree"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtbuild1-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('dtbuild2', type='build')
+    depends_on('dtlink2')
+    depends_on('dtrun2', type='run')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtbuild2/package.py b/var/spack/repos/builtin.mock/packages/dtbuild2/package.py
new file mode 100644
index 0000000000..cf3bb82a10
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtbuild2/package.py
@@ -0,0 +1,13 @@
+from spack import *
+
+
+class Dtbuild2(Package):
+    """Simple package which acts as a build dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtbuild2-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtbuild3/package.py b/var/spack/repos/builtin.mock/packages/dtbuild3/package.py
new file mode 100644
index 0000000000..6ba7e69a41
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtbuild3/package.py
@@ -0,0 +1,13 @@
+from spack import *
+
+
+class Dtbuild3(Package):
+    """Simple package which acts as a build dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtbuild3-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtlink1/package.py b/var/spack/repos/builtin.mock/packages/dtlink1/package.py
new file mode 100644
index 0000000000..2747dcf354
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtlink1/package.py
@@ -0,0 +1,15 @@
+from spack import *
+
+
+class Dtlink1(Package):
+    """Simple package which acts as a link dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtlink1-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('dtlink3')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtlink2/package.py b/var/spack/repos/builtin.mock/packages/dtlink2/package.py
new file mode 100644
index 0000000000..b80bad053f
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtlink2/package.py
@@ -0,0 +1,13 @@
+from spack import *
+
+
+class Dtlink2(Package):
+    """Simple package which acts as a link dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtlink2-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtlink3/package.py b/var/spack/repos/builtin.mock/packages/dtlink3/package.py
new file mode 100644
index 0000000000..bee8b4b8f8
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtlink3/package.py
@@ -0,0 +1,16 @@
+from spack import *
+
+
+class Dtlink3(Package):
+    """Simple package which acts as a link dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtlink3-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('dtbuild2', type='build')
+    depends_on('dtlink4')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtlink4/package.py b/var/spack/repos/builtin.mock/packages/dtlink4/package.py
new file mode 100644
index 0000000000..3f05d5c0d6
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtlink4/package.py
@@ -0,0 +1,13 @@
+from spack import *
+
+
+class Dtlink4(Package):
+    """Simple package which acts as a link dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtlink4-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtlink5/package.py b/var/spack/repos/builtin.mock/packages/dtlink5/package.py
new file mode 100644
index 0000000000..c8b1e97d37
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtlink5/package.py
@@ -0,0 +1,13 @@
+from spack import *
+
+
+class Dtlink5(Package):
+    """Simple package which acts as a link dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtlink5-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtrun1/package.py b/var/spack/repos/builtin.mock/packages/dtrun1/package.py
new file mode 100644
index 0000000000..fb33b9b2f2
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtrun1/package.py
@@ -0,0 +1,16 @@
+from spack import *
+
+
+class Dtrun1(Package):
+    """Simple package which acts as a run dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtrun1-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('dtlink5')
+    depends_on('dtrun3', type='run')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtrun2/package.py b/var/spack/repos/builtin.mock/packages/dtrun2/package.py
new file mode 100644
index 0000000000..e5d4b5e0b4
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtrun2/package.py
@@ -0,0 +1,13 @@
+from spack import *
+
+
+class Dtrun2(Package):
+    """Simple package which acts as a run dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtrun2-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtrun3/package.py b/var/spack/repos/builtin.mock/packages/dtrun3/package.py
new file mode 100644
index 0000000000..70dacf45ff
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtrun3/package.py
@@ -0,0 +1,15 @@
+from spack import *
+
+
+class Dtrun3(Package):
+    """Simple package which acts as a run dependency"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtrun3-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('dtbuild3', type='build')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dttop/package.py b/var/spack/repos/builtin.mock/packages/dttop/package.py
new file mode 100644
index 0000000000..202a3b6883
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dttop/package.py
@@ -0,0 +1,17 @@
+from spack import *
+
+
+class Dttop(Package):
+    """Package with a complicated dependency tree"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dttop-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('dtbuild1', type='build')
+    depends_on('dtlink1')
+    depends_on('dtrun1', type='run')
+
+    def install(self, spec, prefix):
+        pass
diff --git a/var/spack/repos/builtin.mock/packages/dtuse/package.py b/var/spack/repos/builtin.mock/packages/dtuse/package.py
new file mode 100644
index 0000000000..bd7391cee8
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/dtuse/package.py
@@ -0,0 +1,15 @@
+from spack import *
+
+
+class Dtuse(Package):
+    """Simple package which uses dttop"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dtuse-1.0.tar.gz"
+
+    version('1.0', '0123456789abcdef0123456789abcdef')
+
+    depends_on('dttop')
+
+    def install(self, spec, prefix):
+        pass