Remove the spack.architecture module (#25986)

The `spack.architecture` module contains an `Arch` class that is very similar to `spack.spec.ArchSpec` but points to platform, operating system and target objects rather than "names". There's a TODO in the class since 2016:

https://github.com/spack/spack/blob/abb0f6e27c45758c37fd45d663214b86413fb4f6/lib/spack/spack/architecture.py#L70-L75

and this PR basically addresses that. Since there are just a few places where the `Arch` class was used, here we query the relevant platform objects where they are needed directly from `spack.platforms`. This permits to clean the code from vestigial logic.

Modifications:
- [x] Remove the `spack.architecture` module and replace its use by `spack.platforms`
- [x] Remove unneeded tests

37 files changed, 280 insertions, 439 deletions

diff --git a/lib/spack/docs/developer_guide.rst b/lib/spack/docs/developer_guide.rst
index cc77666846..2530b4ef03 100644
--- a/lib/spack/docs/developer_guide.rst
+++ b/lib/spack/docs/developer_guide.rst
@@ -210,15 +210,6 @@ Spec-related modules
      but compilers aren't fully integrated with the build process
      yet.
 
-:mod:`spack.architecture`
-  :func:`architecture.default_arch <spack.architecture.default_arch>` is used
-  to determine the host architecture while building.
-
-  .. warning::
-
-     Not yet implemented.  Should eventually have architecture
-     descriptions for cross-compiling.
-
 ^^^^^^^^^^^^^^^^^
 Build environment
 ^^^^^^^^^^^^^^^^^
diff --git a/lib/spack/spack/architecture.py b/lib/spack/spack/architecture.py
deleted file mode 100644
index 0ae99959bd..0000000000
--- a/lib/spack/spack/architecture.py
+++ /dev/null
@@ -1,242 +0,0 @@
-# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
-# Spack Project Developers. See the top-level COPYRIGHT file for details.
-#
-# SPDX-License-Identifier: (Apache-2.0 OR MIT)
-"""Aggregate the target processor, the operating system and the target
-platform into an architecture object.
-
-On a multiple architecture machine, the architecture spec field can be set to
-build a package against any target and operating system that is present on the
-platform. On Cray platforms or any other architecture that has different front
-and back end environments, the operating system will determine the method of
-compiler detection.
-
-There are two different types of compiler detection:
-
-    1. Through the $PATH env variable (front-end detection)
-    2. Through the module system. (back-end detection)
-
-Depending on which operating system is specified, the compiler will be detected
-using one of those methods.
-
-For platforms such as linux and darwin, the operating system is autodetected.
-
-The command line syntax for specifying an architecture is as follows:
-
-    target=<Target name> os=<OperatingSystem name>
-
-If the user wishes to use the defaults, either target or os can be left out of
-the command line and Spack will concretize using the default. These defaults
-are set in the 'platforms/' directory which contains the different subclasses
-for platforms. If the machine has multiple architectures, the user can
-also enter frontend, or fe or backend or be. These settings will concretize
-to their respective frontend and backend targets and operating systems.
-
-Platforms are an abstract class that are extended by subclasses. If the user
-wants to add a new type of platform (such as cray_xe), they can create a
-subclass and set all the class attributes such as priority, front_target,
-back_target, front_os, back_os. Platforms also contain a priority class
-attribute. A lower number signifies higher priority. These numbers are
-arbitrarily set and can be changed though often there isn't much need unless a
-new platform is added and the user wants that to be detected first.
-
-Targets are created inside the platform subclasses. Most architecture
-(like linux, and darwin) will have only one target family (x86_64) but in the case of
-Cray machines, there is both a frontend and backend processor. The user can
-specify which targets are present on front-end and back-end architecture
-
-Depending on the platform, operating systems are either autodetected or are
-set. The user can set the frontend and backend operating setting by the class
-attributes front_os and back_os. The operating system as described earlier,
-will be responsible for compiler detection.
-"""
-import contextlib
-
-import archspec.cpu
-
-import llnl.util.lang as lang
-
-import spack.compiler
-import spack.compilers
-import spack.config
-import spack.operating_systems
-import spack.platforms
-import spack.spec
-import spack.target
-import spack.util.spack_yaml as syaml
-import spack.version
-
-
-@lang.lazy_lexicographic_ordering
-class Arch(object):
-    """Architecture is now a class to help with setting attributes.
-
-    TODO: refactor so that we don't need this class.
-    """
-
-    def __init__(self, plat=None, os=None, target=None):
-        self.platform = plat
-        if plat and os:
-            os = self.platform.operating_system(os)
-        self.os = os
-        if plat and target:
-            target = self.platform.target(target)
-        self.target = target
-
-        # Hooks for parser to use when platform is set after target or os
-        self.target_string = None
-        self.os_string = None
-
-    @property
-    def concrete(self):
-        return all(
-            (self.platform is not None,
-             isinstance(self.platform, spack.platforms.Platform),
-             self.os is not None,
-             isinstance(self.os, spack.operating_systems.OperatingSystem),
-             self.target is not None, isinstance(self.target, spack.target.Target))
-        )
-
-    def __str__(self):
-        if self.platform or self.os or self.target:
-            if self.platform.name == 'darwin':
-                os_name = self.os.name if self.os else "None"
-            else:
-                os_name = str(self.os)
-
-            return (str(self.platform) + "-" +
-                    os_name + "-" + str(self.target))
-        else:
-            return ''
-
-    def __contains__(self, string):
-        return string in str(self)
-
-    # TODO: make this unnecessary: don't include an empty arch on *every* spec.
-    def __nonzero__(self):
-        return (self.platform is not None or
-                self.os is not None or
-                self.target is not None)
-    __bool__ = __nonzero__
-
-    def _cmp_iter(self):
-        if isinstance(self.platform, spack.platforms.Platform):
-            yield self.platform.name
-        else:
-            yield self.platform
-
-        if isinstance(self.os, spack.operating_systems.OperatingSystem):
-            yield self.os.name
-        else:
-            yield self.os
-
-        if isinstance(self.target, spack.target.Target):
-            yield self.target.microarchitecture
-        else:
-            yield self.target
-
-    def to_dict(self):
-        str_or_none = lambda v: str(v) if v else None
-        d = syaml.syaml_dict([
-            ('platform', str_or_none(self.platform)),
-            ('platform_os', str_or_none(self.os)),
-            ('target', self.target.to_dict_or_value())])
-        return syaml.syaml_dict([('arch', d)])
-
-    def to_spec(self):
-        """Convert this Arch to an anonymous Spec with architecture defined."""
-        spec = spack.spec.Spec()
-        spec.architecture = spack.spec.ArchSpec(str(self))
-        return spec
-
-    @staticmethod
-    def from_dict(d):
-        spec = spack.spec.ArchSpec.from_dict(d)
-        return arch_for_spec(spec)
-
-
-def arch_for_spec(arch_spec):
-    """Transforms the given architecture spec into an architecture object."""
-    arch_spec = spack.spec.ArchSpec(arch_spec)
-    assert arch_spec.concrete
-
-    arch_plat = spack.platforms.by_name(arch_spec.platform)
-    if not (arch_plat.operating_system(arch_spec.os) and
-            arch_plat.target(arch_spec.target)):
-        sys_type = str(default_arch())
-        msg = ("Can't recreate arch for spec {0} on current arch {1}; "
-               "spec architecture is too different")
-        raise ValueError(msg.format(arch_spec, sys_type))
-
-    return Arch(arch_plat, arch_spec.os, arch_spec.target)
-
-
-@lang.memoized
-def _platform():
-    return spack.platforms.host()
-
-
-#: The "real" platform of the host running Spack. This should not be changed
-#: by any method and is here as a convenient way to refer to the host platform.
-real_platform = _platform
-
-#: The current platform used by Spack. May be swapped by the use_platform
-#: context manager.
-platform = _platform
-
-
-@lang.memoized
-def default_arch():
-    """Default ``Arch`` object for this machine"""
-    return Arch(platform(), 'default_os', 'default_target')
-
-
-@lang.memoized
-def compatible_sys_types():
-    """Return a list of all the platform-os-target tuples compatible
-    with the current host.
-    """
-    current_host = archspec.cpu.host()
-    compatible_targets = [current_host] + current_host.ancestors
-    compatible_archs = [
-        str(Arch(platform(), 'default_os', target)) for target in compatible_targets
-    ]
-    return compatible_archs
-
-
-class _PickleableCallable(object):
-    """Class used to pickle a callable that may substitute either
-    _platform or _all_platforms. Lambda or nested functions are
-    not pickleable.
-    """
-    def __init__(self, return_value):
-        self.return_value = return_value
-
-    def __call__(self):
-        return self.return_value
-
-
-@contextlib.contextmanager
-def use_platform(new_platform):
-    global platform
-
-    msg = '"{0}" must be an instance of Platform'
-    assert isinstance(new_platform, spack.platforms.Platform), msg.format(new_platform)
-
-    original_platform_fn = platform
-
-    try:
-        platform = _PickleableCallable(new_platform)
-
-        # Clear configuration and compiler caches
-        spack.config.config.clear_caches()
-        spack.compilers._cache_config_files = []
-
-        yield new_platform
-
-    finally:
-        platform = original_platform_fn
-
-        # Clear configuration and compiler caches
-        spack.config.config.clear_caches()
-        spack.compilers._cache_config_files = []
diff --git a/lib/spack/spack/bootstrap.py b/lib/spack/spack/bootstrap.py
index 76fc6f487f..3fad57b5ae 100644
--- a/lib/spack/spack/bootstrap.py
+++ b/lib/spack/spack/bootstrap.py
@@ -23,7 +23,6 @@ import archspec.cpu
 import llnl.util.filesystem as fs
 import llnl.util.tty as tty
 
-import spack.architecture
 import spack.binary_distribution
 import spack.config
 import spack.detection
@@ -65,10 +64,10 @@ def _try_import_from_store(module, abstract_spec_str):
         module: Python module to be imported
         abstract_spec_str: abstract spec that may provide the module
     """
-    bincache_platform = spack.architecture.real_platform()
+    bincache_platform = spack.platforms.real_host()
     if str(bincache_platform) == 'cray':
         bincache_platform = spack.platforms.linux.Linux()
-        with spack.architecture.use_platform(bincache_platform):
+        with spack.platforms.use_platform(bincache_platform):
             abstract_spec_str = str(spack.spec.Spec(abstract_spec_str))
 
     # We have to run as part of this python interpreter
@@ -191,10 +190,10 @@ class _BuildcacheBootstrapper(object):
         )
 
         # On Cray we want to use Linux binaries if available from mirrors
-        bincache_platform = spack.architecture.real_platform()
+        bincache_platform = spack.platforms.real_host()
         if str(bincache_platform) == 'cray':
             bincache_platform = spack.platforms.Linux()
-            with spack.architecture.use_platform(bincache_platform):
+            with spack.platforms.use_platform(bincache_platform):
                 abstract_spec = spack.spec.Spec(
                     abstract_spec_str + ' ^' + spec_for_current_python()
                 )
@@ -249,7 +248,7 @@ class _BuildcacheBootstrapper(object):
                         "spec": str(index_spec.compiler),
                         "target": str(index_spec.target.family)
                     }
-                    with spack.architecture.use_platform(bincache_platform):
+                    with spack.platforms.use_platform(bincache_platform):
                         with spack.config.override(
                                 'compilers', [{'compiler': compiler_entry}]
                         ):
@@ -287,7 +286,7 @@ class _SourceBootstrapper(object):
         # Try to build and install from sources
         with spack_python_interpreter():
             # Add hint to use frontend operating system on Cray
-            if str(spack.architecture.platform()) == 'cray':
+            if str(spack.platforms.host()) == 'cray':
                 abstract_spec_str += ' os=fe'
 
             concrete_spec = spack.spec.Spec(
@@ -502,7 +501,7 @@ def _bootstrap_config_scopes():
         ('bootstrap', _config_path())
     )
     for name, path in configuration_paths:
-        platform = spack.architecture.platform().name
+        platform = spack.platforms.host().name
         platform_scope = spack.config.ConfigScope(
             '/'.join([name, platform]), os.path.join(path, platform)
         )
@@ -515,11 +514,7 @@ def _bootstrap_config_scopes():
 
 
 def _add_compilers_if_missing():
-    # Do not use spack.architecture.default_arch() since it memoize the result
-    arch = spack.architecture.Arch(
-        spack.architecture.real_platform(), 'default_os', 'default_target'
-    )
-    arch = spack.spec.ArchSpec(str(arch))  # The call below expects an ArchSpec object
+    arch = spack.spec.ArchSpec.frontend_arch()
     if not spack.compilers.compilers_for_arch(arch):
         new_compilers = spack.compilers.find_new_compilers()
         if new_compilers:
@@ -540,7 +535,7 @@ def ensure_bootstrap_configuration():
     bootstrap_store_path = store_path()
     user_configuration = _read_and_sanitize_configuration()
     with spack.environment.no_active_environment():
-        with spack.architecture.use_platform(spack.architecture.real_platform()):
+        with spack.platforms.use_platform(spack.platforms.real_host()):
             with spack.repo.use_repositories(spack.paths.packages_path):
                 with spack.store.use_store(bootstrap_store_path):
                     # Default configuration scopes excluding command line
@@ -611,7 +606,7 @@ def clingo_root_spec():
 
     # Add a proper compiler hint to the root spec. We use GCC for
     # everything but MacOS.
-    if str(spack.architecture.platform()) == 'darwin':
+    if str(spack.platforms.host()) == 'darwin':
         spec_str += ' %apple-clang'
     else:
         spec_str += ' %gcc'
diff --git a/lib/spack/spack/build_environment.py b/lib/spack/spack/build_environment.py
index 68fa77a532..55ba2d3934 100644
--- a/lib/spack/spack/build_environment.py
+++ b/lib/spack/spack/build_environment.py
@@ -49,7 +49,6 @@ from llnl.util.lang import dedupe
 from llnl.util.tty.color import cescape, colorize
 from llnl.util.tty.log import MultiProcessFd
 
-import spack.architecture as arch
 import spack.build_systems.cmake
 import spack.build_systems.meson
 import spack.config
@@ -57,6 +56,7 @@ import spack.install_test
 import spack.main
 import spack.package
 import spack.paths
+import spack.platforms
 import spack.repo
 import spack.schema.environment
 import spack.store
@@ -148,9 +148,10 @@ class MakeExecutable(Executable):
 
 
 def _on_cray():
-    hostarch = arch.Arch(arch.platform(), 'default_os', 'default_target')
-    on_cray = str(hostarch.platform) == 'cray'
-    using_cnl = re.match(r'cnl\d+', str(hostarch.os))
+    host_platform = spack.platforms.host()
+    host_os = host_platform.operating_system('default_os')
+    on_cray = str(host_platform) == 'cray'
+    using_cnl = re.match(r'cnl\d+', str(host_os))
     return on_cray, using_cnl
 
 
@@ -780,7 +781,9 @@ def setup_package(pkg, dirty, context='build'):
         pkg.spec, context, custom_mods_only=False))
 
     # architecture specific setup
-    pkg.architecture.platform.setup_platform_environment(pkg, env)
+    platform = spack.platforms.by_name(pkg.spec.architecture.platform)
+    target = platform.target(pkg.spec.architecture.target)
+    platform.setup_platform_environment(pkg, env)
 
     if context == 'build':
         pkg.setup_build_environment(env)
@@ -813,8 +816,8 @@ def setup_package(pkg, dirty, context='build'):
     if on_cray:
         module('unload', 'cray-libsci')
 
-    if pkg.architecture.target.module_name:
-        load_module(pkg.architecture.target.module_name)
+    if target.module_name:
+        load_module(target.module_name)
 
     load_external_modules(pkg)
 
diff --git a/lib/spack/spack/cmd/arch.py b/lib/spack/spack/cmd/arch.py
index 14be456e3f..29b35000f0 100644
--- a/lib/spack/spack/cmd/arch.py
+++ b/lib/spack/spack/cmd/arch.py
@@ -12,7 +12,7 @@ import archspec.cpu
 import llnl.util.tty.colify as colify
 import llnl.util.tty.color as color
 
-import spack.architecture as architecture
+import spack.platforms
 
 description = "print architecture information about this machine"
 section = "system"
@@ -78,21 +78,24 @@ def arch(parser, args):
         display_targets(archspec.cpu.TARGETS)
         return
 
+    os_args, target_args = 'default_os', 'default_target'
     if args.frontend:
-        arch = architecture.Arch(architecture.platform(),
-                                 'frontend', 'frontend')
+        os_args, target_args = 'frontend', 'frontend'
     elif args.backend:
-        arch = architecture.Arch(architecture.platform(),
-                                 'backend', 'backend')
-    else:
-        arch = architecture.Arch(architecture.platform(),
-                                 'default_os', 'default_target')
+        os_args, target_args = 'backend', 'backend'
+
+    host_platform = spack.platforms.host()
+    host_os = host_platform.operating_system(os_args)
+    host_target = host_platform.target(target_args)
+    architecture = spack.spec.ArchSpec(
+        (str(host_platform), str(host_os), str(host_target))
+    )
 
     if args.platform:
-        print(arch.platform)
+        print(architecture.platform)
     elif args.operating_system:
-        print(arch.os)
+        print(architecture.os)
     elif args.target:
-        print(arch.target)
+        print(architecture.target)
     else:
-        print(arch)
+        print(architecture)
diff --git a/lib/spack/spack/cmd/buildcache.py b/lib/spack/spack/cmd/buildcache.py
index b14652aaee..889c93d690 100644
--- a/lib/spack/spack/cmd/buildcache.py
+++ b/lib/spack/spack/cmd/buildcache.py
@@ -10,7 +10,6 @@ import tempfile
 
 import llnl.util.tty as tty
 
-import spack.architecture
 import spack.binary_distribution as bindist
 import spack.cmd
 import spack.cmd.common.arguments as arguments
@@ -337,7 +336,7 @@ def match_downloaded_specs(pkgs, allow_multiple_matches=False, force=False,
 
     specs = bindist.update_cache_and_get_specs()
     if not other_arch:
-        arch = spack.architecture.default_arch().to_spec()
+        arch = spack.spec.Spec.default_arch()
         specs = [s for s in specs if s.satisfies(arch)]
 
     for pkg in pkgs:
@@ -563,7 +562,7 @@ def listspecs(args):
     """list binary packages available from mirrors"""
     specs = bindist.update_cache_and_get_specs()
     if not args.allarch:
-        arch = spack.architecture.default_arch().to_spec()
+        arch = spack.spec.Spec.default_arch()
         specs = [s for s in specs if s.satisfies(arch)]
 
     if args.specs:
diff --git a/lib/spack/spack/cmd/debug.py b/lib/spack/spack/cmd/debug.py
index dff9cd6f8e..7d86511345 100644
--- a/lib/spack/spack/cmd/debug.py
+++ b/lib/spack/spack/cmd/debug.py
@@ -14,9 +14,9 @@ from glob import glob
 import llnl.util.tty as tty
 from llnl.util.filesystem import working_dir
 
-import spack.architecture as architecture
 import spack.config
 import spack.paths
+import spack.platforms
 from spack.main import get_version
 from spack.util.executable import which
 
@@ -87,10 +87,15 @@ def create_db_tarball(args):
 
 
 def report(args):
+    host_platform = spack.platforms.host()
+    host_os = host_platform.operating_system('frontend')
+    host_target = host_platform.target('frontend')
+    architecture = spack.spec.ArchSpec(
+        (str(host_platform), str(host_os), str(host_target))
+    )
     print('* **Spack:**', get_version())
     print('* **Python:**', platform.python_version())
-    print('* **Platform:**', architecture.Arch(
-        architecture.platform(), 'frontend', 'frontend'))
+    print('* **Platform:**', architecture)
     print('* **Concretizer:**', spack.config.get('config:concretizer'))
 
 
diff --git a/lib/spack/spack/compiler.py b/lib/spack/spack/compiler.py
index d3410bba2d..f137281221 100644
--- a/lib/spack/spack/compiler.py
+++ b/lib/spack/spack/compiler.py
@@ -16,7 +16,6 @@ import llnl.util.lang
 import llnl.util.tty as tty
 from llnl.util.filesystem import path_contains_subdirectory, paths_containing_libs
 
-import spack.architecture
 import spack.compilers
 import spack.error
 import spack.spec
diff --git a/lib/spack/spack/compilers/__init__.py b/lib/spack/spack/compilers/__init__.py
index 9ecfa69393..c76fb0c715 100644
--- a/lib/spack/spack/compilers/__init__.py
+++ b/lib/spack/spack/compilers/__init__.py
@@ -20,11 +20,11 @@ import llnl.util.filesystem as fs
 import llnl.util.lang
 import llnl.util.tty as tty
 
-import spack.architecture
 import spack.compiler
 import spack.config
 import spack.error
 import spack.paths
+import spack.platforms
 import spack.spec
 from spack.util.environment import get_path
 from spack.util.naming import mod_to_class
@@ -519,7 +519,7 @@ def all_os_classes():
     """
     classes = []
 
-    platform = spack.architecture.platform()
+    platform = spack.platforms.host()
     for os_class in platform.operating_sys.values():
         classes.append(os_class)
 
diff --git a/lib/spack/spack/concretize.py b/lib/spack/spack/concretize.py
index fe7bf6406d..905037787f 100644
--- a/lib/spack/spack/concretize.py
+++ b/lib/spack/spack/concretize.py
@@ -31,10 +31,10 @@ import llnl.util.lang
 import llnl.util.tty as tty
 
 import spack.abi
-import spack.architecture
 import spack.compilers
 import spack.environment
 import spack.error
+import spack.platforms
 import spack.repo
 import spack.spec
 import spack.target
@@ -269,7 +269,7 @@ class Concretizer(object):
                 new_plat = spack.platforms.by_name(platform_spec.architecture.platform)
             else:
                 # If no platform anywhere in this spec, grab the default
-                new_plat = spack.architecture.platform()
+                new_plat = spack.platforms.host()
 
         # Get nearest spec with relevant platform and an os
         # Generally, same algorithm as finding platform, except we only
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index 8d028ce0cc..470a2b958c 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -47,9 +47,9 @@ import llnl.util.lang
 import llnl.util.tty as tty
 from llnl.util.filesystem import mkdirp
 
-import spack.architecture
 import spack.compilers
 import spack.paths
+import spack.platforms
 import spack.schema
 import spack.schema.bootstrap
 import spack.schema.compilers
@@ -769,7 +769,7 @@ command_line_scopes = []  # type: List[str]
 
 def _add_platform_scope(cfg, scope_type, name, path):
     """Add a platform-specific subdirectory for the current platform."""
-    platform = spack.architecture.platform().name
+    platform = spack.platforms.host().name
     plat_name = '%s/%s' % (name, platform)
     plat_path = os.path.join(path, platform)
     cfg.push_scope(scope_type(plat_name, plat_path))
diff --git a/lib/spack/spack/main.py b/lib/spack/spack/main.py
index b0c665df0d..5224f42345 100644
--- a/lib/spack/spack/main.py
+++ b/lib/spack/spack/main.py
@@ -26,19 +26,21 @@ from six import StringIO
 import archspec.cpu
 
 import llnl.util.filesystem as fs
+import llnl.util.lang
 import llnl.util.tty as tty
 import llnl.util.tty.colify
 import llnl.util.tty.color as color
 from llnl.util.tty.log import log_output
 
 import spack
-import spack.architecture
 import spack.cmd
 import spack.config
 import spack.environment as ev
 import spack.modules
 import spack.paths
+import spack.platforms
 import spack.repo
+import spack.spec
 import spack.store
 import spack.util.debug
 import spack.util.executable as exe
@@ -644,6 +646,23 @@ def _profile_wrapper(command, parser, args, unknown_args):
         stats.print_stats(nlines)
 
 
+@llnl.util.lang.memoized
+def _compatible_sys_types():
+    """Return a list of all the platform-os-target tuples compatible
+    with the current host.
+    """
+    host_platform = spack.platforms.host()
+    host_os = str(host_platform.operating_system('default_os'))
+    host_target = archspec.cpu.host()
+    compatible_targets = [host_target] + host_target.ancestors
+
+    compatible_archs = [
+        str(spack.spec.ArchSpec((str(host_platform), host_os, str(target))))
+        for target in compatible_targets
+    ]
+    return compatible_archs
+
+
 def print_setup_info(*info):
     """Print basic information needed by setup-env.[c]sh.
 
@@ -653,7 +672,6 @@ def print_setup_info(*info):
 
     This is in ``main.py`` to make it fast; the setup scripts need to
     invoke spack in login scripts, and it needs to be quick.
-
     """
     shell = 'csh' if 'csh' in info else 'sh'
 
@@ -666,9 +684,8 @@ def print_setup_info(*info):
             tty.die('shell must be sh or csh')
 
     # print sys type
-    shell_set('_sp_sys_type', str(spack.architecture.default_arch()))
-    shell_set('_sp_compatible_sys_types',
-              ':'.join(spack.architecture.compatible_sys_types()))
+    shell_set('_sp_sys_type', str(spack.spec.ArchSpec.default_arch()))
+    shell_set('_sp_compatible_sys_types', ':'.join(_compatible_sys_types()))
     # print roots for all module systems
     module_to_roots = {
         'tcl': list(),
diff --git a/lib/spack/spack/operating_systems/_operating_system.py b/lib/spack/spack/operating_systems/_operating_system.py
index d667dea4ab..d496db46da 100644
--- a/lib/spack/spack/operating_systems/_operating_system.py
+++ b/lib/spack/spack/operating_systems/_operating_system.py
@@ -11,10 +11,22 @@ import spack.util.spack_yaml as syaml
 class OperatingSystem(object):
     """Base class for all the Operating Systems.
 
-     Each Operating System contain its own compiler finding logic, that is used
-     to detect compilers.
-    """
+    On a multiple architecture machine, the architecture spec field can be set to
+    build a package against any target and operating system that is present on the
+    platform. On Cray platforms or any other architecture that has different front
+    and back end environments, the operating system will determine the method of
+    compiler detection.
+
+    There are two different types of compiler detection:
+
+        1. Through the $PATH env variable (front-end detection)
+        2. Through the module system. (back-end detection)
 
+    Depending on which operating system is specified, the compiler will be detected
+    using one of those methods.
+
+    For platforms such as linux and darwin, the operating system is autodetected.
+    """
     def __init__(self, name, version):
         self.name = name.replace('-', '_')
         self.version = str(version).replace('-', '_')
diff --git a/lib/spack/spack/package.py b/lib/spack/spack/package.py
index 22ebbe76a1..5a0924707d 100644
--- a/lib/spack/spack/package.py
+++ b/lib/spack/spack/package.py
@@ -1266,14 +1266,6 @@ class PackageBase(six.with_metaclass(PackageMeta, PackageViewMixin, object)):
         """Get the prefix into which this package should be installed."""
         return self.spec.prefix
 
-    @property
-    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  # type: ignore
     @memoized
     def compiler(self):
diff --git a/lib/spack/spack/platforms/__init__.py b/lib/spack/spack/platforms/__init__.py
index 799b9c3171..a73199c887 100644
--- a/lib/spack/spack/platforms/__init__.py
+++ b/lib/spack/spack/platforms/__init__.py
@@ -2,8 +2,9 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-import llnl.util.lang
+import contextlib
 
+from ._functions import _host, by_name, platforms
 from ._platform import Platform
 from .cray import Cray
 from .darwin import Darwin
@@ -15,41 +16,57 @@ __all__ = [
     'Cray',
     'Darwin',
     'Linux',
-    'Test'
+    'Test',
+    'platforms',
+    'host',
+    'by_name'
 ]
 
-#: List of all the platform classes known to Spack
-platforms = [Cray, Darwin, Linux, Test]
+#: The "real" platform of the host running Spack. This should not be changed
+#: by any method and is here as a convenient way to refer to the host platform.
+real_host = _host
 
+#: The current platform used by Spack. May be swapped by the use_platform
+#: context manager.
+host = _host
 
-def host():
-    """Detect and return the platform for this machine or None if detection fails."""
-    for platform_cls in sorted(platforms, key=lambda plt: plt.priority):
-        if platform_cls.detect():
-            return platform_cls()
-    return None
 
+class _PickleableCallable(object):
+    """Class used to pickle a callable that may substitute either
+    _platform or _all_platforms. Lambda or nested functions are
+    not pickleable.
+    """
+    def __init__(self, return_value):
+        self.return_value = return_value
 
-@llnl.util.lang.memoized
-def cls_by_name(name):
-    """Return a platform class that corresponds to the given name or None
-    if there is no match.
+    def __call__(self):
+        return self.return_value
 
-    Args:
-        name (str): name of the platform
-    """
-    for platform_cls in sorted(platforms, key=lambda plt: plt.priority):
-        if name.replace("_", "").lower() == platform_cls.__name__.lower():
-            return platform_cls
-    return None
 
+@contextlib.contextmanager
+def use_platform(new_platform):
+    global host
 
-def by_name(name):
-    """Return a platform object that corresponds to the given name or None
-    if there is no match.
+    import spack.compilers
+    import spack.config
 
-    Args:
-        name (str): name of the platform
-    """
-    platform_cls = cls_by_name(name)
-    return platform_cls() if platform_cls else None
+    msg = '"{0}" must be an instance of Platform'
+    assert isinstance(new_platform, Platform), msg.format(new_platform)
+
+    original_host_fn = host
+
+    try:
+        host = _PickleableCallable(new_platform)
+
+        # Clear configuration and compiler caches
+        spack.config.config.clear_caches()
+        spack.compilers._cache_config_files = []
+
+        yield new_platform
+
+    finally:
+        host = original_host_fn
+
+        # Clear configuration and compiler caches
+        spack.config.config.clear_caches()
+        spack.compilers._cache_config_files = []
diff --git a/lib/spack/spack/platforms/_functions.py b/lib/spack/spack/platforms/_functions.py
new file mode 100644
index 0000000000..17dfbb5d67
--- /dev/null
+++ b/lib/spack/spack/platforms/_functions.py
@@ -0,0 +1,46 @@
+# Copyright 2013-2021 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+import llnl.util.lang
+
+from .cray import Cray
+from .darwin import Darwin
+from .linux import Linux
+from .test import Test
+
+#: List of all the platform classes known to Spack
+platforms = [Cray, Darwin, Linux, Test]
+
+
+def _host():
+    """Detect and return the platform for this machine or None if detection fails."""
+    for platform_cls in sorted(platforms, key=lambda plt: plt.priority):
+        if platform_cls.detect():
+            return platform_cls()
+    return None
+
+
+@llnl.util.lang.memoized
+def cls_by_name(name):
+    """Return a platform class that corresponds to the given name or None
+    if there is no match.
+
+    Args:
+        name (str): name of the platform
+    """
+    for platform_cls in sorted(platforms, key=lambda plt: plt.priority):
+        if name.replace("_", "").lower() == platform_cls.__name__.lower():
+            return platform_cls
+    return None
+
+
+def by_name(name):
+    """Return a platform object that corresponds to the given name or None
+    if there is no match.
+
+    Args:
+        name (str): name of the platform
+    """
+    platform_cls = cls_by_name(name)
+    return platform_cls() if platform_cls else None
diff --git a/lib/spack/spack/platforms/_platform.py b/lib/spack/spack/platforms/_platform.py
index c2ee536b2b..8c44b3c51d 100644
--- a/lib/spack/spack/platforms/_platform.py
+++ b/lib/spack/spack/platforms/_platform.py
@@ -15,7 +15,26 @@ class NoPlatformError(spack.error.SpackError):
 
 @llnl.util.lang.lazy_lexicographic_ordering
 class Platform(object):
-    """Base class for each type of Platform"""
+    """Platform is an abstract class extended by subclasses.
+
+    To add a new type of platform (such as cray_xe), create a subclass and set all the
+    class attributes such as priority, front_target, back_target, front_os, back_os.
+
+    Platform also contain a priority class attribute. A lower number signifies higher
+    priority. These numbers are arbitrarily set and can be changed though often there
+    isn't much need unless a new platform is added and the user wants that to be
+    detected first.
+
+    Targets are created inside the platform subclasses. Most architecture (like linux,
+    and darwin) will have only one target family (x86_64) but in the case of Cray
+    machines, there is both a frontend and backend processor. The user can specify
+    which targets are present on front-end and back-end architecture.
+
+    Depending on the platform, operating systems are either autodetected or are
+    set. The user can set the frontend and backend operating setting by the class
+    attributes front_os and back_os. The operating system will be responsible for
+    compiler detection.
+    """
 
     # Subclass sets number. Controls detection order
     priority = None   # type: int
diff --git a/lib/spack/spack/relocate.py b/lib/spack/spack/relocate.py
index af2c4bedc3..bbfc4bd52f 100644
--- a/lib/spack/spack/relocate.py
+++ b/lib/spack/spack/relocate.py
@@ -15,7 +15,7 @@ from ordereddict_backport import OrderedDict
 import llnl.util.lang
 import llnl.util.tty as tty
 
-import spack.architecture
+import spack.platforms
 import spack.repo
 import spack.spec
 import spack.util.executable as executable
@@ -94,7 +94,7 @@ def _patchelf():
         return exe_path
 
     # Skip darwin
-    if str(spack.architecture.platform()) == 'darwin':
+    if str(spack.platforms.host()) == 'darwin':
         return None
 
     # Install the spec and return its path
diff --git a/lib/spack/spack/solver/asp.py b/lib/spack/spack/solver/asp.py
index 790e545878..c091d0b89d 100644
--- a/lib/spack/spack/solver/asp.py
+++ b/lib/spack/spack/solver/asp.py
@@ -30,7 +30,6 @@ import llnl.util.lang
 import llnl.util.tty as tty
 
 import spack
-import spack.architecture
 import spack.bootstrap
 import spack.cmd
 import spack.compilers
@@ -41,6 +40,7 @@ import spack.environment as ev
 import spack.error
 import spack.package
 import spack.package_prefs
+import spack.platforms
 import spack.repo
 import spack.spec
 import spack.util.timer
@@ -1086,12 +1086,12 @@ class SpackSolverSetup(object):
 
     def platform_defaults(self):
         self.gen.h2('Default platform')
-        platform = spack.architecture.platform()
+        platform = spack.platforms.host()
         self.gen.fact(fn.node_platform_default(platform))
 
     def os_defaults(self, specs):
         self.gen.h2('Possible operating systems')
-        platform = spack.architecture.platform()
+        platform = spack.platforms.host()
 
         # create set of OS's to consider
         possible = set([
@@ -1111,7 +1111,7 @@ class SpackSolverSetup(object):
         """Add facts about targets and target compatibility."""
         self.gen.h2('Default target')
 
-        platform = spack.architecture.platform()
+        platform = spack.platforms.host()
         uarch = archspec.cpu.TARGETS.get(platform.default)
 
         self.gen.h2('Target compatibility')
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 15df0e69cd..ff71662a03 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -92,7 +92,6 @@ import llnl.util.lang as lang
 import llnl.util.tty as tty
 import llnl.util.tty.color as clr
 
-import spack.architecture
 import spack.compiler
 import spack.compilers
 import spack.config
@@ -213,6 +212,27 @@ def colorize_spec(spec):
 
 @lang.lazy_lexicographic_ordering
 class ArchSpec(object):
+    """Aggregate the target platform, the operating system and the target
+    microarchitecture into an architecture spec..
+    """
+    @staticmethod
+    def _return_arch(os_tag, target_tag):
+        platform = spack.platforms.host()
+        default_os = platform.operating_system(os_tag)
+        default_target = platform.target(target_tag)
+        arch_tuple = str(platform), str(default_os), str(default_target)
+        return ArchSpec(arch_tuple)
+
+    @staticmethod
+    def default_arch():
+        """Return the default architecture"""
+        return ArchSpec._return_arch('default_os', 'default_target')
+
+    @staticmethod
+    def frontend_arch():
+        """Return the frontend architecture"""
+        return ArchSpec._return_arch('frontend', 'frontend')
+
     def __init__(self, spec_or_platform_tuple=(None, None, None)):
         """ Architecture specification a package should be built with.
 
@@ -294,7 +314,7 @@ class ArchSpec(object):
         value = str(value) if value is not None else None
 
         if value in spack.platforms.Platform.reserved_oss:
-            curr_platform = str(spack.architecture.platform())
+            curr_platform = str(spack.platforms.host())
             self.platform = self.platform or curr_platform
 
             if self.platform != curr_platform:
@@ -331,7 +351,7 @@ class ArchSpec(object):
         value = target_or_none(value)
 
         if str(value) in spack.platforms.Platform.reserved_targets:
-            curr_platform = str(spack.architecture.platform())
+            curr_platform = str(spack.platforms.host())
             self.platform = self.platform or curr_platform
 
             if self.platform != curr_platform:
@@ -1020,6 +1040,13 @@ class Spec(object):
     #: Cache for spec's prefix, computed lazily in the corresponding property
     _prefix = None
 
+    @staticmethod
+    def default_arch():
+        """Return an anonymous spec for the default architecture"""
+        s = Spec()
+        s.architecture = ArchSpec.default_arch()
+        return s
+
     def __init__(self, spec_like=None, normal=False,
                  concrete=False, external_path=None, external_modules=None):
         """Create a new Spec.
@@ -1242,7 +1269,7 @@ class Spec(object):
         """
         arch = self.architecture
         if arch and not arch.platform and (arch.os or arch.target):
-            self._set_architecture(platform=spack.architecture.platform().name)
+            self._set_architecture(platform=spack.platforms.host().name)
 
     #
     # Public interface
diff --git a/lib/spack/spack/subprocess_context.py b/lib/spack/spack/subprocess_context.py
index 9e3e3581f6..f0d942abc0 100644
--- a/lib/spack/spack/subprocess_context.py
+++ b/lib/spack/spack/subprocess_context.py
@@ -20,10 +20,10 @@ import pydoc
 import sys
 from types import ModuleType
 
-import spack.architecture
 import spack.config
 import spack.environment
 import spack.main
+import spack.platforms
 import spack.repo
 import spack.store
 
@@ -96,7 +96,7 @@ class TestState(object):
         if _serialize:
             self.repo_dirs = list(r.root for r in spack.repo.path.repos)
             self.config = spack.config.config
-            self.platform = spack.architecture.platform
+            self.platform = spack.platforms.host
             self.test_patches = store_patches()
             self.store_token = spack.store.store.serialize()
 
@@ -104,7 +104,7 @@ class TestState(object):
         if _serialize:
             spack.repo.path = spack.repo._path(self.repo_dirs)
             spack.config.config = self.config
-            spack.architecture.platform = self.platform
+            spack.platforms.host = self.platform
 
             new_store = spack.store.Store.deserialize(self.store_token)
             spack.store.store = new_store
diff --git a/lib/spack/spack/test/architecture.py b/lib/spack/spack/test/architecture.py
index fd65c9558c..b44c0b5f3d 100644
--- a/lib/spack/spack/test/architecture.py
+++ b/lib/spack/spack/test/architecture.py
@@ -7,7 +7,6 @@ import platform
 
 import pytest
 
-import spack.architecture
 import spack.concretize
 import spack.operating_systems
 import spack.platforms
@@ -16,16 +15,6 @@ import spack.target
 
 
 @pytest.fixture
-def sample_arch():
-    """Sample test architecture"""
-    arch = spack.architecture.Arch()
-    arch.platform = spack.architecture.platform()
-    arch.os = arch.platform.operating_system('default_os')
-    arch.target = arch.platform.target('default_target')
-    return arch
-
-
-@pytest.fixture
 def current_host_platform():
     """Return the platform of the current host as detected by the
     'platform' stdlib package.
@@ -61,41 +50,12 @@ def os_str(request):
     return str(request.param)
 
 
-def test_dict_round_trip(sample_arch):
-    """Check that a round trip through dict return an equivalent architecture"""
-    sample_arch_copy = spack.architecture.Arch.from_dict(sample_arch.to_dict())
-
-    assert sample_arch == sample_arch_copy
-    for current_arch in (sample_arch, sample_arch_copy):
-        assert isinstance(current_arch, spack.architecture.Arch)
-        assert isinstance(current_arch.platform, spack.platforms.Platform)
-        assert isinstance(current_arch.os, spack.operating_systems.OperatingSystem)
-        assert isinstance(current_arch.target, spack.target.Target)
-
-
 def test_platform(current_host_platform):
     """Check that current host detection return the correct platform"""
-    detected_platform = spack.architecture.real_platform()
+    detected_platform = spack.platforms.real_host()
     assert str(detected_platform) == str(current_host_platform)
 
 
-@pytest.mark.parametrize('attribute_name,expected', [
-    # Make sure architecture reports that it's False when nothing's set.
-    (None, False),
-    # ... and it reports True otherwise
-    ('platform', True),
-    ('os', True),
-    ('target', True)
-])
-def test_boolness(sample_arch, attribute_name, expected):
-    """Boolean checks on an architecture object"""
-    arch = spack.architecture.Arch()
-    if attribute_name:
-        setattr(arch, attribute_name, getattr(sample_arch, attribute_name))
-
-    assert bool(arch) is expected
-
-
 def test_user_input_combination(config, target_str, os_str):
     """Test for all the valid user input combinations that both the target and
     the operating system match.
diff --git a/lib/spack/spack/test/build_systems.py b/lib/spack/spack/test/build_systems.py
index cd42e7b4e2..b9105538b2 100644
--- a/lib/spack/spack/test/build_systems.py
+++ b/lib/spack/spack/test/build_systems.py
@@ -10,7 +10,6 @@ import pytest
 
 import llnl.util.filesystem as fs
 
-import spack.architecture
 import spack.environment
 import spack.repo
 from spack.build_environment import ChildError, get_std_cmake_args, setup_package
diff --git a/lib/spack/spack/test/cmd/debug.py b/lib/spack/spack/test/cmd/debug.py
index bfb041b272..554b75fc46 100644
--- a/lib/spack/spack/test/cmd/debug.py
+++ b/lib/spack/spack/test/cmd/debug.py
@@ -9,8 +9,8 @@ import platform
 
 import pytest
 
-import spack.architecture as architecture
 import spack.config
+import spack.platforms
 from spack.main import SpackCommand, get_version
 from spack.util.executable import which
 
@@ -48,9 +48,14 @@ def test_create_db_tarball(tmpdir, database):
 
 def test_report():
     out = debug('report')
-    arch = architecture.Arch(architecture.platform(), 'frontend', 'frontend')
+    host_platform = spack.platforms.host()
+    host_os = host_platform.operating_system('frontend')
+    host_target = host_platform.target('frontend')
+    architecture = spack.spec.ArchSpec(
+        (str(host_platform), str(host_os), str(host_target))
+    )
 
     assert get_version() in out
     assert platform.python_version() in out
-    assert str(arch) in out
+    assert str(architecture) in out
     assert spack.config.get('config:concretizer') in out
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index b7ae5dd926..cb09f41c66 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -11,7 +11,6 @@ import archspec.cpu
 
 import llnl.util.lang
 
-import spack.architecture
 import spack.compilers
 import spack.concretize
 import spack.error
@@ -428,7 +427,7 @@ class TestConcretize(object):
     def test_external_package_module(self):
         # No tcl modules on darwin/linux machines
         # TODO: improved way to check for this.
-        platform = spack.architecture.real_platform().name
+        platform = spack.platforms.real_host().name
         if platform == 'darwin' or platform == 'linux':
             return
 
diff --git a/lib/spack/spack/test/conftest.py b/lib/spack/spack/test/conftest.py
index f071d19b06..2d52449fbe 100644
--- a/lib/spack/spack/test/conftest.py
+++ b/lib/spack/spack/test/conftest.py
@@ -24,7 +24,6 @@ import archspec.cpu.schema
 
 from llnl.util.filesystem import mkdirp, remove_linked_tree, working_dir
 
-import spack.architecture
 import spack.binary_distribution
 import spack.caches
 import spack.compilers
@@ -450,7 +449,7 @@ def _use_test_platform(test_platform):
     # This is the only context manager used at session scope (see note
     # below for more insight) since we want to use the test platform as
     # a default during tests.
-    with spack.architecture.use_platform(test_platform):
+    with spack.platforms.use_platform(test_platform):
         yield
 
 #
@@ -515,10 +514,9 @@ def linux_os():
     """Returns a named tuple with attributes 'name' and 'version'
     representing the OS.
     """
-    platform = spack.architecture.platform()
+    platform = spack.platforms.host()
     name, version = 'debian', '6'
     if platform.name == 'linux':
-        platform = spack.architecture.platform()
         current_os = platform.operating_system('default_os')
         name, version = current_os.name, current_os.version
     LinuxOS = collections.namedtuple('LinuxOS', ['name', 'version'])
diff --git a/lib/spack/spack/test/multimethod.py b/lib/spack/spack/test/multimethod.py
index 6169584d96..e1c33ef302 100644
--- a/lib/spack/spack/test/multimethod.py
+++ b/lib/spack/spack/test/multimethod.py
@@ -6,6 +6,7 @@
 """Test for multi_method dispatch."""
 import pytest
 
+import spack.platforms
 import spack.repo
 from spack.multimethod import NoSuchMethodError
 
@@ -79,7 +80,7 @@ def test_default_works(pkg_name):
 
 
 def test_target_match(pkg_name):
-    platform = spack.architecture.platform()
+    platform = spack.platforms.host()
     targets = list(platform.targets.values())
     for target in targets[:-1]:
         pkg = spack.repo.get(pkg_name + ' target=' + target.name)
diff --git a/lib/spack/spack/test/relocate.py b/lib/spack/spack/test/relocate.py
index 8f7e084e4d..2743235174 100644
--- a/lib/spack/spack/test/relocate.py
+++ b/lib/spack/spack/test/relocate.py
@@ -12,7 +12,6 @@ import pytest
 
 import llnl.util.filesystem
 
-import spack.architecture
 import spack.concretize
 import spack.paths
 import spack.relocate
diff --git a/lib/spack/spack/test/spec_dag.py b/lib/spack/spack/test/spec_dag.py
index 080f26000d..4f57dd818d 100644
--- a/lib/spack/spack/test/spec_dag.py
+++ b/lib/spack/spack/test/spec_dag.py
@@ -7,7 +7,6 @@ These tests check Spec DAG operations using dummy packages.
 """
 import pytest
 
-import spack.architecture
 import spack.error
 import spack.package
 import spack.util.hash as hashutil
diff --git a/lib/spack/spack/test/spec_semantics.py b/lib/spack/spack/test/spec_semantics.py
index b9a48aa465..97351b0ce2 100644
--- a/lib/spack/spack/test/spec_semantics.py
+++ b/lib/spack/spack/test/spec_semantics.py
@@ -7,7 +7,6 @@ import sys
 
 import pytest
 
-import spack.architecture
 import spack.directives
 import spack.error
 from spack.error import SpecError, UnsatisfiableSpecError
@@ -690,7 +689,7 @@ class TestSpecSematics(object):
         check_constrain_changed('libelf', 'debug=2')
         check_constrain_changed('libelf', 'cppflags="-O3"')
 
-        platform = spack.architecture.platform()
+        platform = spack.platforms.host()
         check_constrain_changed(
             'libelf', 'target=' + platform.target('default_target').name)
         check_constrain_changed(
@@ -709,7 +708,7 @@ class TestSpecSematics(object):
         check_constrain_not_changed(
             'libelf cppflags="-O3"', 'cppflags="-O3"')
 
-        platform = spack.architecture.platform()
+        platform = spack.platforms.host()
         default_target = platform.target('default_target').name
         check_constrain_not_changed(
             'libelf target=' + default_target, 'target=' + default_target)
@@ -723,7 +722,7 @@ class TestSpecSematics(object):
         check_constrain_changed('libelf^foo', 'libelf^foo~debug')
         check_constrain_changed('libelf', '^foo')
 
-        platform = spack.architecture.platform()
+        platform = spack.platforms.host()
         default_target = platform.target('default_target').name
         check_constrain_changed(
             'libelf^foo', 'libelf^foo target=' + default_target)
@@ -742,7 +741,7 @@ class TestSpecSematics(object):
         check_constrain_not_changed(
             'libelf^foo cppflags="-O3"', 'libelf^foo cppflags="-O3"')
 
-        platform = spack.architecture.platform()
+        platform = spack.platforms.host()
         default_target = platform.target('default_target').name
         check_constrain_not_changed(
             'libelf^foo target=' + default_target,
diff --git a/lib/spack/spack/test/spec_yaml.py b/lib/spack/spack/test/spec_yaml.py
index d297cb45a8..c34a1d548c 100644
--- a/lib/spack/spack/test/spec_yaml.py
+++ b/lib/spack/spack/test/spec_yaml.py
@@ -15,7 +15,6 @@ import sys
 
 import pytest
 
-import spack.architecture
 import spack.hash_types as ht
 import spack.spec
 import spack.util.spack_json as sjson
@@ -226,7 +225,6 @@ def test_ordered_read_not_required_for_consistent_dag_hash(
 
 @pytest.mark.parametrize("module", [
     spack.spec,
-    spack.architecture,
     spack.version,
 ])
 def test_hashes_use_no_python_dicts(module):
diff --git a/lib/spack/spack/util/environment.py b/lib/spack/spack/util/environment.py
index 075d7e88ea..ef9f1a8b1b 100644
--- a/lib/spack/spack/util/environment.py
+++ b/lib/spack/spack/util/environment.py
@@ -2,7 +2,6 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 """Utilities for setting and modifying environment variables."""
 import collections
 import contextlib
@@ -22,6 +21,8 @@ from six.moves import shlex_quote as cmd_quote
 import llnl.util.tty as tty
 from llnl.util.lang import dedupe
 
+import spack.platforms
+import spack.spec
 import spack.util.executable as executable
 
 system_paths = ['/', '/usr', '/usr/local']
@@ -158,18 +159,20 @@ def get_host_environment():
     """Return a dictionary (lookup) with host information (not including the
     os.environ).
     """
-    import spack.architecture as architecture
-    import spack.spec
-    arch = architecture.Arch(
-        architecture.platform(), 'default_os', 'default_target')
-    arch_spec = spack.spec.Spec('arch=%s' % arch)
+    host_platform = spack.platforms.host()
+    host_target = host_platform.target('default_target')
+    host_os = host_platform.operating_system('default_os')
+    arch_fmt = 'platform={0} os={1} target={2}'
+    arch_spec = spack.spec.Spec(
+        arch_fmt.format(host_platform, host_os, host_target)
+    )
     return {
-        'target': str(arch.target),
-        'os': str(arch.os),
-        'platform': str(arch.platform),
+        'target': str(host_target),
+        'os': str(host_os),
+        'platform': str(host_platform),
         'arch': arch_spec,
         'architecture': arch_spec,
-        'arch_str': str(arch),
+        'arch_str': str(arch_spec),
         'hostname': socket.gethostname()
     }
 
diff --git a/var/spack/repos/builtin.mock/packages/multimethod/package.py b/var/spack/repos/builtin.mock/packages/multimethod/package.py
index 8ae2bd1bbe..492ae0853f 100644
--- a/var/spack/repos/builtin.mock/packages/multimethod/package.py
+++ b/var/spack/repos/builtin.mock/packages/multimethod/package.py
@@ -5,7 +5,7 @@
 
 from six import string_types
 
-import spack.architecture
+import spack.platforms
 from spack import *
 from spack.pkg.builtin.mock.multimethod_base import MultimethodBase
 
@@ -83,7 +83,7 @@ class Multimethod(MultimethodBase):
     #
     # Make sure we can switch methods on different target
     #
-    platform = spack.architecture.platform()
+    platform = spack.platforms.host()
     targets = list(platform.targets.values())
     if len(targets) > 1:
         targets = targets[:-1]
diff --git a/var/spack/repos/builtin/packages/arm/package.py b/var/spack/repos/builtin/packages/arm/package.py
index c1d149d80f..fcb9530ec9 100644
--- a/var/spack/repos/builtin/packages/arm/package.py
+++ b/var/spack/repos/builtin/packages/arm/package.py
@@ -43,7 +43,7 @@ _versions = {
 
 
 def get_os():
-    spack_os = spack.architecture.platform().default_os
+    spack_os = spack.platforms.host().default_os
     return _os_map.get(spack_os, 'RHEL-7')
 
 
diff --git a/var/spack/repos/builtin/packages/gcc/package.py b/var/spack/repos/builtin/packages/gcc/package.py
index 307cd75404..d8772b215e 100644
--- a/var/spack/repos/builtin/packages/gcc/package.py
+++ b/var/spack/repos/builtin/packages/gcc/package.py
@@ -10,7 +10,7 @@ import sys
 
 import llnl.util.tty as tty
 
-import spack.architecture
+import spack.platforms
 import spack.util.executable
 from spack.operating_systems.mac_os import macos_sdk_path, macos_version
 
@@ -324,7 +324,7 @@ class Gcc(AutotoolsPackage, GNUMirrorPackage):
                 continue
             # Filter out links in favor of real executables on
             # all systems but Cray
-            host_platform = str(spack.architecture.platform())
+            host_platform = str(spack.platforms.host())
             if os.path.islink(exe) and host_platform != 'cray':
                 continue
 
diff --git a/var/spack/repos/builtin/packages/sqlite/package.py b/var/spack/repos/builtin/packages/sqlite/package.py
index 53e24e1c48..7f7948a39e 100644
--- a/var/spack/repos/builtin/packages/sqlite/package.py
+++ b/var/spack/repos/builtin/packages/sqlite/package.py
@@ -2,12 +2,11 @@
 # Spack Project Developers. See the top-level COPYRIGHT file for details.
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
-
 import os
 import re
 from tempfile import NamedTemporaryFile
 
-from spack import architecture
+import spack.platforms
 
 
 class Sqlite(AutotoolsPackage):
@@ -168,9 +167,8 @@ class Sqlite(AutotoolsPackage):
         return find_libraries('libsqlite3', root=self.prefix.lib)
 
     def get_arch(self):
-        arch = architecture.Arch()
-        arch.platform = architecture.platform()
-        return str(arch.platform.target('default_target'))
+        host_platform = spack.platforms.host()
+        return str(host_platform.target('default_target'))
 
     def configure_args(self):
         args = []
diff --git a/var/spack/repos/builtin/packages/upcxx/package.py b/var/spack/repos/builtin/packages/upcxx/package.py
index 5b55de5c2f..2661be4283 100644
--- a/var/spack/repos/builtin/packages/upcxx/package.py
+++ b/var/spack/repos/builtin/packages/upcxx/package.py
@@ -7,7 +7,7 @@ from spack import *
 
 
 def cross_detect():
-    if spack.architecture.platform().name == 'cray':
+    if spack.platforms.host().name == 'cray':
         if which('srun'):
             return 'cray-aries-slurm'
         if which('aprun'):