Fixes to Handling Multiple Architectures (#2261)

* Added some notes about how multiarch detection could be fixed.

* Implemented a preliminary version of the "spack.spec.ArchSpec" class.

* Updated the "spack.spec.Spec" class to use "ArchSpec" instead of "Arch".

* Fixed a number of small bugs in the "spack.spec.ArchSpec" class.

* Fixed the 'Concretizer.concretize_architecture' method so that it uses the new architecture specs.

* Updated the package class to properly use arch specs.
Removed a number of unused architecture functions.

* Fixed up a number of bugs that were causing the regression tests to fail.
Added a couple of additional regression tests related to architecture parsing/specification.
Fixed a few bugs with setting reserved os/target values on "ArchSpec" objects.
Removed a number of unnecessary functions in the "spack.architecture" and "spack.concretize" modules.

* Fixed a few bugs with reading architecture information from specs.
Updated the tests to use a uniform architecture to improve reliability.
Fixed a few minor style issues.

* Adapted the compiler component of Spack to use arch specs.

* Implemented more test cases for the extended architecture spec features.
Improved error detection for multiple arch components in a spec.

* Fix for backwards compatibility with v0.8 and prior

* Changed os to unknown for compatibility specs

* Use `spack09` instead of `spackcompat` for the platform of old specs.

13 files changed, 473 insertions, 272 deletions

diff --git a/lib/spack/spack/architecture.py b/lib/spack/spack/architecture.py
index b14de35109..6ea7bafb6a 100644
--- a/lib/spack/spack/architecture.py
+++ b/lib/spack/spack/architecture.py
@@ -126,8 +126,7 @@ class Target(object):
 @key_ordering
 class Platform(object):
     """ Abstract class that each type of Platform will subclass.
-        Will return a instance of it once it
-        is returned
+        Will return a instance of it once it is returned.
     """
 
     priority        = None  # Subclass sets number. Controls detection order
@@ -139,6 +138,9 @@ class Platform(object):
     back_os         = None
     default_os      = None
 
+    reserved_targets = ['default_target', 'frontend', 'fe', 'backend', 'be']
+    reserved_oss = ['default_os', 'frontend', 'fe', 'backend', 'be']
+
     def __init__(self, name):
         self.targets = {}
         self.operating_sys = {}
@@ -149,7 +151,7 @@ class Platform(object):
         Raises an error if the platform specifies a name
         that is reserved by spack as an alias.
         """
-        if name in ['frontend', 'fe', 'backend', 'be', 'default_target']:
+        if name in Platform.reserved_targets:
             raise ValueError(
                 "%s is a spack reserved alias "
                 "and cannot be the name of a target" % name)
@@ -174,7 +176,7 @@ class Platform(object):
         """ Add the operating_system class object into the
             platform.operating_sys dictionary
         """
-        if name in ['frontend', 'fe', 'backend', 'be', 'default_os']:
+        if name in Platform.reserved_oss:
             raise ValueError(
                 "%s is a spack reserved alias "
                 "and cannot be the name of an OS" % name)
@@ -241,7 +243,7 @@ class OperatingSystem(object):
         self.version = version
 
     def __str__(self):
-        return self.name + self.version
+        return "%s%s" % (self.name, self.version)
 
     def __repr__(self):
         return self.__str__()
@@ -409,86 +411,52 @@ class Arch(object):
         return (platform, platform_os, target)
 
     def to_dict(self):
-        return syaml_dict((
-            ('platform',
-             str(self.platform) if self.platform else None),
-            ('platform_os',
-             str(self.platform_os) if self.platform_os else None),
-            ('target',
-             str(self.target) if self.target else None)))
-
-
-def _target_from_dict(target_name, plat=None):
-    """ Creates new instance of target and assigns all the attributes of
-        that target from the dictionary
-    """
-    if not plat:
-        plat = platform()
-    return plat.target(target_name)
+        str_or_none = lambda v: str(v) if v else None
+        d = syaml_dict([
+            ('platform', str_or_none(self.platform)),
+            ('platform_os', str_or_none(self.platform_os)),
+            ('target', str_or_none(self.target))])
+        return syaml_dict([('arch', d)])
 
+    @staticmethod
+    def from_dict(d):
+        spec = spack.spec.ArchSpec.from_dict(d)
+        return arch_for_spec(spec)
 
-def _operating_system_from_dict(os_name, plat=None):
-    """ uses platform's operating system method to grab the constructed
-        operating systems that are valid on the platform.
-    """
-    if not plat:
-        plat = platform()
-    if isinstance(os_name, dict):
-        name = os_name['name']
-        version = os_name['version']
-        return plat.operating_system(name + version)
-    else:
-        return plat.operating_system(os_name)
-
-
-def _platform_from_dict(platform_name):
-    """ Constructs a platform from a dictionary. """
+
+def get_platform(platform_name):
+    """Returns a platform object that corresponds to the given name."""
     platform_list = all_platforms()
     for p in platform_list:
         if platform_name.replace("_", "").lower() == p.__name__.lower():
             return p()
 
 
-def arch_from_dict(d):
-    """ Uses _platform_from_dict, _operating_system_from_dict, _target_from_dict
-        helper methods to recreate the arch tuple from the dictionary read from
-        a yaml file
+def verify_platform(platform_name):
+    """ Determines whether or not the platform with the given name is supported
+        in Spack.  For more information, see the 'spack.platforms' submodule.
     """
-    arch = Arch()
-
-    if isinstance(d, basestring):
-        # We have an old spec using a string for the architecture
-        arch.platform = Platform('spack_compatibility')
-        arch.platform_os = OperatingSystem('unknown', '')
-        arch.target = Target(d)
-
-        arch.os_string = None
-        arch.target_string = None
-    else:
-        if d is None:
-            return None
-        platform_name = d['platform']
-        os_name = d['platform_os']
-        target_name = d['target']
-
-        if platform_name:
-            arch.platform = _platform_from_dict(platform_name)
-        else:
-            arch.platform = None
-        if target_name:
-            arch.target = _target_from_dict(target_name, arch.platform)
-        else:
-            arch.target = None
-        if os_name:
-            arch.platform_os = _operating_system_from_dict(os_name,
-                                                           arch.platform)
-        else:
-            arch.platform_os = None
+    platform_name = platform_name.replace("_", "").lower()
+    platform_names = [p.__name__.lower() for p in all_platforms()]
+
+    if platform_name not in platform_names:
+        tty.die("%s is not a supported platform; supported platforms are %s" %
+                (platform_name, platform_names))
+
+
+def arch_for_spec(arch_spec):
+    """Transforms the given architecture spec into an architecture objct."""
+    arch_spec = spack.spec.ArchSpec(arch_spec)
+    assert(arch_spec.concrete)
 
-        arch.os_string = None
-        arch.target_string = None
+    arch_plat = get_platform(arch_spec.platform)
+    if not (arch_plat.operating_system(arch_spec.platform_os) and
+            arch_plat.target(arch_spec.target)):
+        raise ValueError(
+            "Can't recreate arch for spec %s on current arch %s; "
+            "spec architecture is too different" % (arch_spec, sys_type()))
 
-    return arch
+    return Arch(arch_plat, arch_spec.platform_os, arch_spec.target)
 
 
 @memoized
diff --git a/lib/spack/spack/build_environment.py b/lib/spack/spack/build_environment.py
index 49df7a90b4..5e99d4552b 100644
--- a/lib/spack/spack/build_environment.py
+++ b/lib/spack/spack/build_environment.py
@@ -339,7 +339,7 @@ def set_build_environment_variables(pkg, env, dirty=False):
             if os.path.isdir(pcdir):
                 env.prepend_path('PKG_CONFIG_PATH', pcdir)
 
-    if pkg.spec.architecture.target.module_name:
+    if pkg.architecture.target.module_name:
         load_module(pkg.spec.architecture.target.module_name)
 
     return env
@@ -492,7 +492,7 @@ def setup_package(pkg, dirty=False):
 
     set_compiler_environment_variables(pkg, spack_env)
     set_build_environment_variables(pkg, spack_env, dirty)
-    pkg.spec.architecture.platform.setup_platform_environment(pkg, spack_env)
+    pkg.architecture.platform.setup_platform_environment(pkg, spack_env)
     load_external_modules(pkg)
     # traverse in postorder so package can use vars from its dependencies
     spec = pkg.spec
diff --git a/lib/spack/spack/compiler.py b/lib/spack/spack/compiler.py
index 5170872cf7..4a7ee614d3 100644
--- a/lib/spack/spack/compiler.py
+++ b/lib/spack/spack/compiler.py
@@ -115,8 +115,8 @@ class Compiler(object):
     def __init__(self, cspec, operating_system,
                  paths, modules=[], alias=None, environment=None,
                  extra_rpaths=None, **kwargs):
-        self.operating_system = operating_system
         self.spec = cspec
+        self.operating_system = str(operating_system)
         self.modules = modules
         self.alias = alias
 
diff --git a/lib/spack/spack/compilers/__init__.py b/lib/spack/spack/compilers/__init__.py
index 5b049367cc..9a9036da83 100644
--- a/lib/spack/spack/compilers/__init__.py
+++ b/lib/spack/spack/compilers/__init__.py
@@ -202,20 +202,23 @@ def find(compiler_spec, scope=None):
 
 
 @_auto_compiler_spec
-def compilers_for_spec(compiler_spec, scope=None, **kwargs):
+def compilers_for_spec(compiler_spec, arch_spec=None, scope=None):
     """This gets all compilers that satisfy the supplied CompilerSpec.
        Returns an empty list if none are found.
     """
-    platform = kwargs.get('platform', None)
     config = all_compilers_config(scope)
 
     def get_compilers(cspec):
         compilers = []
 
         for items in config:
-            if items['compiler']['spec'] != str(cspec):
-                continue
             items = items['compiler']
+            if items['spec'] != str(cspec):
+                continue
+
+            os = items.get('operating_system', None)
+            if arch_spec and os != arch_spec.platform_os:
+                continue
 
             if not ('paths' in items and
                     all(n in items['paths'] for n in _path_instance_vars)):
@@ -235,11 +238,6 @@ def compilers_for_spec(compiler_spec, scope=None, **kwargs):
             if mods == 'None':
                 mods = []
 
-            os = None
-            if 'operating_system' in items:
-                os = spack.architecture._operating_system_from_dict(
-                    items['operating_system'], platform)
-
             alias = items.get('alias', None)
             compiler_flags = items.get('flags', {})
             environment = items.get('environment', {})
@@ -259,17 +257,15 @@ def compilers_for_spec(compiler_spec, scope=None, **kwargs):
 
 
 @_auto_compiler_spec
-def compiler_for_spec(compiler_spec, arch):
+def compiler_for_spec(compiler_spec, arch_spec):
     """Get the compiler that satisfies compiler_spec.  compiler_spec must
        be concrete."""
-    operating_system = arch.platform_os
     assert(compiler_spec.concrete)
+    assert(arch_spec.concrete)
 
-    compilers = [
-        c for c in compilers_for_spec(compiler_spec, platform=arch.platform)
-        if c.operating_system == operating_system]
+    compilers = compilers_for_spec(compiler_spec, arch_spec=arch_spec)
     if len(compilers) < 1:
-        raise NoCompilerForSpecError(compiler_spec, operating_system)
+        raise NoCompilerForSpecError(compiler_spec, arch_spec.platform_os)
     if len(compilers) > 1:
         raise CompilerSpecInsufficientlySpecificError(compiler_spec)
     return compilers[0]
diff --git a/lib/spack/spack/concretize.py b/lib/spack/spack/concretize.py
index dcea147814..1bc933e543 100644
--- a/lib/spack/spack/concretize.py
+++ b/lib/spack/spack/concretize.py
@@ -240,47 +240,6 @@ class DefaultConcretizer(object):
 
         return True   # Things changed
 
-    def _concretize_operating_system(self, spec):
-        if spec.architecture.platform_os is not None and isinstance(
-                spec.architecture.platform_os,
-                spack.architecture.OperatingSystem):
-            return False
-
-        if spec.root.architecture and spec.root.architecture.platform_os:
-            if isinstance(spec.root.architecture.platform_os,
-                          spack.architecture.OperatingSystem):
-                spec.architecture.platform_os = \
-                    spec.root.architecture.platform_os
-        else:
-            spec.architecture.platform_os = \
-                spec.architecture.platform.operating_system('default_os')
-        return True  # changed
-
-    def _concretize_target(self, spec):
-        if spec.architecture.target is not None and isinstance(
-                spec.architecture.target, spack.architecture.Target):
-            return False
-        if spec.root.architecture and spec.root.architecture.target:
-            if isinstance(spec.root.architecture.target,
-                          spack.architecture.Target):
-                spec.architecture.target = spec.root.architecture.target
-        else:
-            spec.architecture.target = spec.architecture.platform.target(
-                'default_target')
-        return True  # changed
-
-    def _concretize_platform(self, spec):
-        if spec.architecture.platform is not None and isinstance(
-                spec.architecture.platform, spack.architecture.Platform):
-            return False
-        if spec.root.architecture and spec.root.architecture.platform:
-            if isinstance(spec.root.architecture.platform,
-                          spack.architecture.Platform):
-                spec.architecture.platform = spec.root.architecture.platform
-        else:
-            spec.architecture.platform = spack.architecture.platform()
-        return True  # changed?
-
     def concretize_architecture(self, spec):
         """If the spec is empty provide the defaults of the platform. If the
         architecture is not a basestring, then check if either the platform,
@@ -292,16 +251,25 @@ class DefaultConcretizer(object):
         DAG has an architecture, then use the root otherwise use the defaults
         on the platform.
         """
+        root_arch = spec.root.architecture
+        sys_arch = spack.spec.ArchSpec(spack.architecture.sys_type())
+        spec_changed = False
+
         if spec.architecture is None:
-            # Set the architecture to all defaults
-            spec.architecture = spack.architecture.Arch()
-            return True
+            spec.architecture = spack.spec.ArchSpec(sys_arch)
+            spec_changed = True
 
-        # Concretize the operating_system and target based of the spec
-        ret = any((self._concretize_platform(spec),
-                   self._concretize_operating_system(spec),
-                   self._concretize_target(spec)))
-        return ret
+        default_archs = [root_arch, sys_arch]
+        while not spec.architecture.concrete and default_archs:
+            arch = default_archs.pop(0)
+
+            replacement_fields = [k for k, v in arch.to_cmp_dict().iteritems()
+                                  if v and not getattr(spec.architecture, k)]
+            for field in replacement_fields:
+                setattr(spec.architecture, field, getattr(arch, field))
+                spec_changed = True
+
+        return spec_changed
 
     def concretize_variants(self, spec):
         """If the spec already has variants filled in, return.  Otherwise, add
@@ -343,13 +311,8 @@ class DefaultConcretizer(object):
         # Takes advantage of the proper logic already existing in
         # compiler_for_spec Should think whether this can be more
         # efficient
-        def _proper_compiler_style(cspec, arch):
-            platform = arch.platform
-            compilers = spack.compilers.compilers_for_spec(cspec,
-                                                           platform=platform)
-            return filter(lambda c: c.operating_system ==
-                          arch.platform_os, compilers)
-            # return compilers
+        def _proper_compiler_style(cspec, aspec):
+            return spack.compilers.compilers_for_spec(cspec, arch_spec=aspec)
 
         all_compilers = spack.compilers.all_compilers()
 
diff --git a/lib/spack/spack/package.py b/lib/spack/spack/package.py
index 8bb19042cc..9c946844c6 100644
--- a/lib/spack/spack/package.py
+++ b/lib/spack/spack/package.py
@@ -898,7 +898,14 @@ class PackageBase(object):
         return self.spec.prefix
 
     @property
-    # TODO: Change this to architecture
+    def architecture(self):
+        """Get the spack.architecture.Arch object that represents the
+        environment in which this package will be built."""
+        if not self.spec.concrete:
+            raise ValueError("Can only get the arch for concrete package.")
+        return spack.architecture.arch_for_spec(self.spec.architecture)
+
+    @property
     def compiler(self):
         """Get the spack.compiler.Compiler object used to build this package"""
         if not self.spec.concrete:
diff --git a/lib/spack/spack/platforms/test.py b/lib/spack/spack/platforms/test.py
index c918211555..a40e1f3b44 100644
--- a/lib/spack/spack/platforms/test.py
+++ b/lib/spack/spack/platforms/test.py
@@ -23,8 +23,7 @@
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
 from spack.architecture import Platform, Target
-from spack.operating_systems.linux_distro import LinuxDistro
-from spack.operating_systems.cnl import Cnl
+from spack.architecture import OperatingSystem as OS
 
 
 class Test(Platform):
@@ -33,18 +32,17 @@ class Test(Platform):
     back_end    = 'x86_64'
     default     = 'x86_64'
 
-    back_os = 'CNL10'
-    default_os = 'CNL10'
+    front_os = 'redhat6'
+    back_os = 'debian6'
+    default_os = 'debian6'
 
     def __init__(self):
         super(Test, self).__init__('test')
         self.add_target(self.default, Target(self.default))
         self.add_target(self.front_end, Target(self.front_end))
 
-        self.add_operating_system(self.default_os, Cnl())
-        linux_dist = LinuxDistro()
-        self.front_os = linux_dist.name
-        self.add_operating_system(self.front_os, linux_dist)
+        self.add_operating_system(self.default_os, OS('debian', 6))
+        self.add_operating_system(self.front_os, OS('redhat', 6))
 
     @classmethod
     def detect(self):
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 951e9ae652..b95f43e901 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -97,7 +97,6 @@ expansion when it is the first character in an id typed on the command line.
 """
 import base64
 import hashlib
-import imp
 import ctypes
 from StringIO import StringIO
 from operator import attrgetter
@@ -105,7 +104,6 @@ from operator import attrgetter
 from yaml.error import MarkedYAMLError
 
 import llnl.util.tty as tty
-from llnl.util.filesystem import join_path
 from llnl.util.lang import *
 from llnl.util.tty.color import *
 
@@ -116,7 +114,6 @@ import spack.compilers as compilers
 import spack.error
 import spack.parse
 from spack.build_environment import get_path_from_module, load_module
-from spack.util.naming import mod_to_class
 from spack.util.prefix import Prefix
 from spack.util.string import *
 import spack.util.spack_yaml as syaml
@@ -256,6 +253,204 @@ def colorize_spec(spec):
 
 
 @key_ordering
+class ArchSpec(object):
+    """ The ArchSpec class represents an abstract architecture specification
+        that a package should be built with.  At its core, each ArchSpec is
+        comprised of three elements: a platform (e.g. Linux), an OS (e.g.
+        RHEL6), and a target (e.g. x86_64).
+    """
+
+    # TODO: Formalize the specifications for architectures and then use
+    # the appropriate parser here to read these specifications.
+    def __init__(self, *args):
+        to_attr_string = lambda s: str(s) if s and s != "None" else None
+
+        self.platform, self.platform_os, self.target = (None, None, None)
+
+        if len(args) == 1:
+            spec_like = args[0]
+            if isinstance(spec_like, ArchSpec):
+                self._dup(spec_like)
+            elif isinstance(spec_like, basestring):
+                spec_fields = spec_like.split("-")
+
+                if len(spec_fields) == 3:
+                    self.platform, self.platform_os, self.target = tuple(
+                        to_attr_string(f) for f in spec_fields)
+                else:
+                    raise ValueError("%s is an invalid arch spec" % spec_like)
+        elif len(args) == 3:
+            self.platform = to_attr_string(args[0])
+            self.platform_os = to_attr_string(args[1])
+            self.target = to_attr_string(args[2])
+        elif len(args) != 0:
+            raise TypeError("Can't make arch spec from %s" % args)
+
+    def _autospec(self, spec_like):
+        if isinstance(spec_like, ArchSpec):
+            return spec_like
+        return ArchSpec(spec_like)
+
+    def _cmp_key(self):
+        return (self.platform, self.platform_os, self.target)
+
+    def _dup(self, other):
+        self.platform = other.platform
+        self.platform_os = other.platform_os
+        self.target = other.target
+
+    @property
+    def platform(self):
+        return self._platform
+
+    @platform.setter
+    def platform(self, value):
+        """ The platform of the architecture spec will be verified as a
+            supported Spack platform before it's set to ensure all specs
+            refer to valid platforms.
+        """
+        value = str(value) if value is not None else None
+        self._platform = value
+
+    @property
+    def platform_os(self):
+        return self._platform_os
+
+    @platform_os.setter
+    def platform_os(self, value):
+        """ The OS of the architecture spec will update the platform field
+            if the OS is set to one of the reserved OS types so that the
+            default OS type can be resolved.  Since the reserved OS
+            information is only available for the host machine, the platform
+            will assumed to be the host machine's platform.
+        """
+        value = str(value) if value is not None else None
+
+        if value in spack.architecture.Platform.reserved_oss:
+            curr_platform = str(spack.architecture.platform())
+            self.platform = self.platform or curr_platform
+
+            if self.platform != curr_platform:
+                raise ValueError(
+                    "Can't set arch spec OS to reserved value '%s' when the "
+                    "arch platform (%s) isn't the current platform (%s)" %
+                    (value, self.platform, curr_platform))
+
+            spec_platform = spack.architecture.get_platform(self.platform)
+            value = str(spec_platform.operating_system(value))
+
+        self._platform_os = value
+
+    @property
+    def target(self):
+        return self._target
+
+    @target.setter
+    def target(self, value):
+        """ The target of the architecture spec will update the platform field
+            if the target is set to one of the reserved target types so that
+            the default target type can be resolved.  Since the reserved target
+            information is only available for the host machine, the platform
+            will assumed to be the host machine's platform.
+        """
+        value = str(value) if value is not None else None
+
+        if value in spack.architecture.Platform.reserved_targets:
+            curr_platform = str(spack.architecture.platform())
+            self.platform = self.platform or curr_platform
+
+            if self.platform != curr_platform:
+                raise ValueError(
+                    "Can't set arch spec target to reserved value '%s' when "
+                    "the arch platform (%s) isn't the current platform (%s)" %
+                    (value, self.platform, curr_platform))
+
+            spec_platform = spack.architecture.get_platform(self.platform)
+            value = str(spec_platform.target(value))
+
+        self._target = value
+
+    def satisfies(self, other, strict=False):
+        other = self._autospec(other)
+        sdict, odict = self.to_cmp_dict(), other.to_cmp_dict()
+
+        if strict or self.concrete:
+            return all(getattr(self, attr) == getattr(other, attr)
+                       for attr in odict if odict[attr])
+        else:
+            return all(getattr(self, attr) == getattr(other, attr)
+                       for attr in odict if sdict[attr] and odict[attr])
+
+    def constrain(self, other):
+        """ Projects all architecture fields that are specified in the given
+            spec onto the instance spec if they're missing from the instance
+            spec. This will only work if the two specs are compatible.
+        """
+        other = self._autospec(other)
+
+        if not self.satisfies(other):
+            raise UnsatisfiableArchitectureSpecError(self, other)
+
+        constrained = False
+        for attr, svalue in self.to_cmp_dict().iteritems():
+            ovalue = getattr(other, attr)
+            if svalue is None and ovalue is not None:
+                setattr(self, attr, ovalue)
+                constrained = True
+
+        return constrained
+
+    def copy(self):
+        clone = ArchSpec.__new__(ArchSpec)
+        clone._dup(self)
+        return clone
+
+    @property
+    def concrete(self):
+        return all(v for k, v in self.to_cmp_dict().iteritems())
+
+    def to_cmp_dict(self):
+        """Returns a dictionary that can be used for field comparison."""
+        return dict([
+            ('platform', self.platform),
+            ('platform_os', self.platform_os),
+            ('target', self.target)])
+
+    def to_dict(self):
+        d = syaml_dict([
+            ('platform', self.platform),
+            ('platform_os', self.platform_os),
+            ('target', self.target)])
+        return syaml_dict([('arch', d)])
+
+    @staticmethod
+    def from_dict(d):
+        """Import an ArchSpec from raw YAML/JSON data.
+
+        This routine implements a measure of compatibility with older
+        versions of Spack.  Spack releases before 0.10 used a single
+        string with no OS or platform identifiers.  We import old Spack
+        architectures with platform ``spack09``, OS ``unknown``, and the
+        old arch string as the target.
+
+        Specs from `0.10` or later have a more fleshed out architecture
+        descriptor with a platform, an OS, and a target.
+
+        """
+        if not isinstance(d['arch'], dict):
+            return ArchSpec('spack09', 'unknown', d['arch'])
+
+        d = d['arch']
+        return ArchSpec(d['platform'], d['platform_os'], d['target'])
+
+    def __str__(self):
+        return "%s-%s-%s" % (self.platform, self.platform_os, self.target)
+
+    def __repr__(self):
+        return str(self)
+
+
+@key_ordering
 class CompilerSpec(object):
     """The CompilerSpec field represents the compiler or range of compiler
        versions that a package should be built with.  CompilerSpecs have a
@@ -664,38 +859,42 @@ class Spec(object):
         """
         valid_flags = FlagMap.valid_compiler_flags()
         if name == 'arch' or name == 'architecture':
-            parts = value.split('-')
-            if len(parts) == 3:
-                platform, op_sys, target = parts
-            else:
-                platform, op_sys, target = None, None, value
-
-            assert(self.architecture.platform is None)
-            assert(self.architecture.platform_os is None)
-            assert(self.architecture.target is None)
-            assert(self.architecture.os_string is None)
-            assert(self.architecture.target_string is None)
-            self._set_platform(platform)
-            self._set_os(op_sys)
-            self._set_target(target)
+            parts = tuple(value.split('-'))
+            plat, os, tgt = parts if len(parts) == 3 else (None, None, value)
+            self._set_architecture(platform=plat, platform_os=os, target=tgt)
         elif name == 'platform':
-            self._set_platform(value)
+            self._set_architecture(platform=value)
         elif name == 'os' or name == 'operating_system':
-            if self.architecture.platform:
-                self._set_os(value)
-            else:
-                self.architecture.os_string = value
+            self._set_architecture(platform_os=value)
         elif name == 'target':
-            if self.architecture.platform:
-                self._set_target(value)
-            else:
-                self.architecture.target_string = value
+            self._set_architecture(target=value)
         elif name in valid_flags:
             assert(self.compiler_flags is not None)
             self.compiler_flags[name] = value.split()
         else:
             self._add_variant(name, value)
 
+    def _set_architecture(self, **kwargs):
+        """Called by the parser to set the architecture."""
+        arch_attrs = ['platform', 'platform_os', 'target']
+        if self.architecture and self.architecture.concrete:
+            raise DuplicateArchitectureError(
+                "Spec for '%s' cannot have two architectures." % self.name)
+
+        if not self.architecture:
+            new_vals = tuple(kwargs.get(arg, None) for arg in arch_attrs)
+            self.architecture = ArchSpec(*new_vals)
+        else:
+            new_attrvals = [(a, v) for a, v in kwargs.iteritems()
+                            if a in arch_attrs]
+            for new_attr, new_value in new_attrvals:
+                if getattr(self.architecture, new_attr):
+                    raise DuplicateArchitectureError(
+                        "Spec for '%s' cannot have two '%s' specified "
+                        "for its architecture" % (self.name, new_attr))
+                else:
+                    setattr(self.architecture, new_attr, new_value)
+
     def _set_compiler(self, compiler):
         """Called by the parser to set the compiler."""
         if self.compiler:
@@ -703,53 +902,6 @@ class Spec(object):
                 "Spec for '%s' cannot have two compilers." % self.name)
         self.compiler = compiler
 
-    def _set_platform(self, value):
-        """Called by the parser to set the architecture platform"""
-        if isinstance(value, basestring):
-            mod_path = spack.platform_path
-            mod_string = 'spack.platformss'
-            names = list_modules(mod_path)
-            if value in names:
-                # Create a platform object from the name
-                mod_name = mod_string + value
-                path = join_path(mod_path, value) + '.py'
-                mod = imp.load_source(mod_name, path)
-                class_name = mod_to_class(value)
-                if not hasattr(mod, class_name):
-                    tty.die(
-                        'No class %s defined in %s' % (class_name, mod_name))
-                cls = getattr(mod, class_name)
-                if not inspect.isclass(cls):
-                    tty.die('%s.%s is not a class' % (mod_name, class_name))
-                platform = cls()
-            else:
-                tty.die("No platform class %s defined." % value)
-        else:
-            # The value is a platform
-            platform = value
-
-        self.architecture.platform = platform
-
-        # Set os and target if we previously got strings for them
-        if self.architecture.os_string:
-            self._set_os(self.architecture.os_string)
-            self.architecture.os_string = None
-        if self.architecture.target_string:
-            self._set_target(self.architecture.target_string)
-            self.architecture.target_string = None
-
-    def _set_os(self, value):
-        """Called by the parser to set the architecture operating system"""
-        arch = self.architecture
-        if arch.platform:
-            arch.platform_os = arch.platform.operating_system(value)
-
-    def _set_target(self, value):
-        """Called by the parser to set the architecture target"""
-        arch = self.architecture
-        if arch.platform:
-            arch.target = arch.platform.target(value)
-
     def _add_dependency(self, spec, deptypes):
         """Called by the parser to add another spec as a dependency."""
         if spec.name in self._dependencies:
@@ -990,6 +1142,9 @@ class Spec(object):
         if self.versions:
             d.update(self.versions.to_dict())
 
+        if self.architecture:
+            d.update(self.architecture.to_dict())
+
         if self.compiler:
             d.update(self.compiler.to_dict())
 
@@ -1002,9 +1157,6 @@ class Spec(object):
         if params:
             d['parameters'] = params
 
-        if self.architecture:
-            d['arch'] = self.architecture.to_dict()
-
         # TODO: restore build dependencies here once we have less picky
         # TODO: concretization.
         deps = self.dependencies_dict(deptype=('link', 'run'))
@@ -1042,7 +1194,7 @@ class Spec(object):
             spec.versions = VersionList.from_dict(node)
 
         if 'arch' in node:
-            spec.architecture = spack.architecture.arch_from_dict(node['arch'])
+            spec.architecture = ArchSpec.from_dict(node)
 
         if 'compiler' in node:
             spec.compiler = CompilerSpec.from_dict(node)
@@ -1861,25 +2013,10 @@ class Spec(object):
 
         # Architecture satisfaction is currently just string equality.
         # If not strict, None means unconstrained.
-        sarch, oarch = self.architecture, other.architecture
-        if sarch and oarch:
-            if ((sarch.platform and
-                 oarch.platform and
-                 sarch.platform != oarch.platform) or
-
-                (sarch.platform_os and
-                 oarch.platform_os and
-                 sarch.platform_os != oarch.platform_os) or
-
-                (sarch.target and
-                 oarch.target and
-                 sarch.target != oarch.target)):
+        if self.architecture and other.architecture:
+            if not self.architecture.satisfies(other.architecture, strict):
                 return False
-
-        elif strict and ((oarch and not sarch) or
-                         (oarch.platform and not sarch.platform) or
-                         (oarch.platform_os and not sarch.platform_os) or
-                         (oarch.target and not sarch.target)):
+        elif strict and (other.architecture and not self.architecture):
             return False
 
         if not self.compiler_flags.satisfies(
@@ -1975,7 +2112,8 @@ class Spec(object):
         # Local node attributes get copied first.
         self.name = other.name
         self.versions = other.versions.copy()
-        self.architecture = other.architecture
+        self.architecture = other.architecture.copy() if other.architecture \
+            else None
         self.compiler = other.compiler.copy() if other.compiler else None
         if cleardeps:
             self._dependents = DependencyMap()
@@ -2540,10 +2678,12 @@ class SpecParser(spack.parse.Parser):
 
         # If the spec has an os or a target and no platform, give it
         # the default platform
+        platform_default = spack.architecture.platform().name
         for spec in specs:
             for s in spec.traverse():
-                if s.architecture.os_string or s.architecture.target_string:
-                    s._set_platform(spack.architecture.platform())
+                if s.architecture and not s.architecture.platform and \
+                        (s.architecture.platform_os or s.architecture.target):
+                    s._set_architecture(platform=platform_default)
         return specs
 
     def parse_compiler(self, text):
@@ -2585,7 +2725,7 @@ class SpecParser(spack.parse.Parser):
         spec.name = spec_name
         spec.versions = VersionList()
         spec.variants = VariantMap(spec)
-        spec.architecture = spack.architecture.Arch()
+        spec.architecture = None
         spec.compiler = None
         spec.external = None
         spec.external_module = None
diff --git a/lib/spack/spack/test/__init__.py b/lib/spack/spack/test/__init__.py
index c0a4c7354f..79122cc1de 100644
--- a/lib/spack/spack/test/__init__.py
+++ b/lib/spack/spack/test/__init__.py
@@ -28,9 +28,11 @@ import os
 import llnl.util.tty as tty
 import nose
 import spack
+import spack.architecture
 from llnl.util.filesystem import join_path
 from llnl.util.tty.colify import colify
 from spack.test.tally_plugin import Tally
+from spack.platforms.test import Test as TestPlatform
 """Names of tests to be included in Spack's test suite"""
 
 # All the tests Spack knows about.
@@ -84,6 +86,13 @@ test_names = [
 ]
 
 
+def setup_tests():
+    """Prepare the environment for the Spack tests to be run."""
+    test_platform = TestPlatform()
+    spack.architecture.real_platform = spack.architecture.platform
+    spack.architecture.platform = lambda: test_platform
+
+
 def list_tests():
     """Return names of all tests that can be run for Spack."""
     return test_names
@@ -117,6 +126,8 @@ def run(names, outputDir, verbose=False):
         runOpts += ["--with-xunit",
                     "--xunit-file={0}".format(xmlOutputPath)]
     argv = [""] + runOpts + modules
+
+    setup_tests()
     nose.run(argv=argv, addplugins=[tally])
 
     succeeded = not tally.failCount and not tally.errorCount
diff --git a/lib/spack/spack/test/architecture.py b/lib/spack/spack/test/architecture.py
index 22ddd4c97e..0ce583c6ea 100644
--- a/lib/spack/spack/test/architecture.py
+++ b/lib/spack/spack/test/architecture.py
@@ -54,10 +54,7 @@ class ArchitectureTest(MockPackagesTest):
         arch.platform_os = arch.platform.operating_system('default_os')
         arch.target = arch.platform.target('default_target')
 
-        d = arch.to_dict()
-
-        new_arch = spack.architecture.arch_from_dict(d)
-
+        new_arch = spack.architecture.Arch.from_dict(arch.to_dict())
         self.assertEqual(arch, new_arch)
 
         self.assertTrue(isinstance(arch, spack.architecture.Arch))
@@ -75,7 +72,7 @@ class ArchitectureTest(MockPackagesTest):
                                    spack.architecture.Target))
 
     def test_platform(self):
-        output_platform_class = spack.architecture.platform()
+        output_platform_class = spack.architecture.real_platform()
         if os.path.exists('/opt/cray/craype'):
             my_platform_class = Cray()
         elif os.path.exists('/bgsys'):
@@ -114,10 +111,12 @@ class ArchitectureTest(MockPackagesTest):
         """Test when user inputs just frontend that both the frontend target
             and frontend operating system match
         """
-        frontend_os = self.platform.operating_system("frontend")
-        frontend_target = self.platform.target("frontend")
+        frontend_os = str(self.platform.operating_system("frontend"))
+        frontend_target = str(self.platform.target("frontend"))
+
         frontend_spec = Spec("libelf os=frontend target=frontend")
         frontend_spec.concretize()
+
         self.assertEqual(frontend_os, frontend_spec.architecture.platform_os)
         self.assertEqual(frontend_target, frontend_spec.architecture.target)
 
@@ -125,19 +124,22 @@ class ArchitectureTest(MockPackagesTest):
         """Test when user inputs backend that both the backend target and
             backend operating system match
         """
-        backend_os = self.platform.operating_system("backend")
-        backend_target = self.platform.target("backend")
+        backend_os = str(self.platform.operating_system("backend"))
+        backend_target = str(self.platform.target("backend"))
+
         backend_spec = Spec("libelf os=backend target=backend")
         backend_spec.concretize()
+
         self.assertEqual(backend_os, backend_spec.architecture.platform_os)
         self.assertEqual(backend_target, backend_spec.architecture.target)
 
     def test_user_defaults(self):
-        default_os = self.platform.operating_system("default_os")
-        default_target = self.platform.target("default_target")
+        default_os = str(self.platform.operating_system("default_os"))
+        default_target = str(self.platform.target("default_target"))
 
         default_spec = Spec("libelf")  # default is no args
         default_spec.concretize()
+
         self.assertEqual(default_os, default_spec.architecture.platform_os)
         self.assertEqual(default_target, default_spec.architecture.target)
 
@@ -156,8 +158,9 @@ class ArchitectureTest(MockPackagesTest):
             spec = Spec("libelf os=%s target=%s" % (o, t))
             spec.concretize()
             results.append(spec.architecture.platform_os ==
-                           self.platform.operating_system(o))
-            results.append(spec.architecture.target == self.platform.target(t))
+                           str(self.platform.operating_system(o)))
+            results.append(spec.architecture.target ==
+                           str(self.platform.target(t)))
         res = all(results)
 
         self.assertTrue(res)
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index 8ecbddbda2..154e0eb68e 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -250,7 +250,7 @@ class ConcretizeTest(MockPackagesTest):
     def test_external_package_module(self):
         # No tcl modules on darwin/linux machines
         # TODO: improved way to check for this.
-        platform = spack.architecture.platform().name
+        platform = spack.architecture.real_platform().name
         if (platform == 'darwin' or platform == 'linux'):
             return
 
diff --git a/lib/spack/spack/test/spec_semantics.py b/lib/spack/spack/test/spec_semantics.py
index 79ffc99298..c165934948 100644
--- a/lib/spack/spack/test/spec_semantics.py
+++ b/lib/spack/spack/test/spec_semantics.py
@@ -133,14 +133,59 @@ class SpecSematicsTest(MockPackagesTest):
 
     def test_satisfies_architecture(self):
         self.check_satisfies(
+            'foo platform=test',
+            'platform=test')
+        self.check_satisfies(
+            'foo platform=linux',
+            'platform=linux')
+        self.check_satisfies(
+            'foo platform=test',
+            'platform=test target=frontend')
+        self.check_satisfies(
+            'foo platform=test',
+            'platform=test os=frontend target=frontend')
+        self.check_satisfies(
+            'foo platform=test os=frontend target=frontend',
+            'platform=test')
+
+        self.check_unsatisfiable(
+            'foo platform=linux',
+            'platform=test os=redhat6 target=x86_32')
+        self.check_unsatisfiable(
+            'foo os=redhat6',
+            'platform=test os=debian6 target=x86_64')
+        self.check_unsatisfiable(
+            'foo target=x86_64',
+            'platform=test os=redhat6 target=x86_32')
+
+        self.check_satisfies(
+            'foo arch=test-None-None',
+            'platform=test')
+        self.check_satisfies(
+            'foo arch=test-None-frontend',
+            'platform=test target=frontend')
+        self.check_satisfies(
+            'foo arch=test-frontend-frontend',
+            'platform=test os=frontend target=frontend')
+        self.check_satisfies(
+            'foo arch=test-frontend-frontend',
+            'platform=test')
+        self.check_unsatisfiable(
+            'foo arch=test-frontend-frontend',
+            'platform=test os=frontend target=backend')
+
+        self.check_satisfies(
             'foo platform=test target=frontend os=frontend',
             'platform=test target=frontend os=frontend')
         self.check_satisfies(
             'foo platform=test target=backend os=backend',
-            'platform=test target=backend', 'platform=test os=backend')
+            'platform=test target=backend os=backend')
         self.check_satisfies(
             'foo platform=test target=default_target os=default_os',
-            'platform=test target=default_target os=default_os')
+            'platform=test os=default_os')
+        self.check_unsatisfiable(
+            'foo platform=test target=x86_32 os=redhat6',
+            'platform=linux target=x86_32 os=redhat6')
 
     def test_satisfies_dependencies(self):
         self.check_satisfies('mpileaks^mpich', '^mpich')
diff --git a/lib/spack/spack/test/spec_syntax.py b/lib/spack/spack/test/spec_syntax.py
index d4eb9e057f..1e072fe970 100644
--- a/lib/spack/spack/test/spec_syntax.py
+++ b/lib/spack/spack/test/spec_syntax.py
@@ -120,6 +120,10 @@ class SpecSyntaxTest(unittest.TestCase):
             'mvapich_foo'
             '^_openmpi@1.2:1.4,1.6%intel@12.1 cppflags="-O3"+debug~qt_4'
             '^stackwalker@8.1_1e')
+        self.check_parse(
+            "mvapich_foo"
+            "^_openmpi@1.2:1.4,1.6%intel@12.1 debug=2~qt_4"
+            "^stackwalker@8.1_1e arch=test-redhat6-x86_32")
 
     def test_canonicalize(self):
         self.check_parse(
@@ -144,6 +148,22 @@ class SpecSyntaxTest(unittest.TestCase):
             "x^y@1,2:3,4%intel@1,2,3,4+a~b+c~d+e~f",
             "x ^y~f+e~d+c~b+a@4,2:3,1%intel@4,3,2,1")
 
+        self.check_parse(
+            "x arch=test-redhat6-None"
+            "^y arch=test-None-x86_64"
+            "^z arch=linux-None-None",
+
+            "x os=fe"
+            "^y target=be"
+            "^z platform=linux")
+
+        self.check_parse(
+            "x arch=test-debian6-x86_64"
+            "^y arch=test-debian6-x86_64",
+
+            "x os=default_os target=default_target"
+            "^y os=default_os target=default_target")
+
         self.check_parse("x^y", "x@: ^y@:")
 
     def test_parse_errors(self):
@@ -169,10 +189,12 @@ class SpecSyntaxTest(unittest.TestCase):
     def test_duplicate_compiler(self):
         self.assertRaises(DuplicateCompilerSpecError,
                           self.check_parse, "x%intel%intel")
+
         self.assertRaises(DuplicateCompilerSpecError,
                           self.check_parse, "x%intel%gcc")
         self.assertRaises(DuplicateCompilerSpecError,
                           self.check_parse, "x%gcc%intel")
+
         self.assertRaises(DuplicateCompilerSpecError,
                           self.check_parse, "x ^y%intel%intel")
         self.assertRaises(DuplicateCompilerSpecError,
@@ -180,6 +202,54 @@ class SpecSyntaxTest(unittest.TestCase):
         self.assertRaises(DuplicateCompilerSpecError,
                           self.check_parse, "x ^y%gcc%intel")
 
+    def test_duplicate_architecture(self):
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x arch=linux-rhel7-x86_64 arch=linux-rhel7-x86_64")
+
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x arch=linux-rhel7-x86_64 arch=linux-rhel7-ppc64le")
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x arch=linux-rhel7-ppc64le arch=linux-rhel7-x86_64")
+
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "y ^x arch=linux-rhel7-x86_64 arch=linux-rhel7-x86_64")
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "y ^x arch=linux-rhel7-x86_64 arch=linux-rhel7-ppc64le")
+
+    def test_duplicate_architecture_component(self):
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x os=fe os=fe")
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x os=fe os=be")
+
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x target=fe target=fe")
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x target=fe target=be")
+
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x platform=test platform=test")
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x platform=test platform=test")
+
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x os=fe platform=test target=fe os=fe")
+        self.assertRaises(
+            DuplicateArchitectureError, self.check_parse,
+            "x target=be platform=test os=be os=fe")
+
     # ========================================================================
     # Lex checks
     # ========================================================================