5 files changed, 23 insertions, 8 deletions
diff --git a/lib/spack/spack/cmd/compiler.py b/lib/spack/spack/cmd/compiler.py
index 625466f8c7..c8f52af04d 100644
--- a/lib/spack/spack/cmd/compiler.py
+++ b/lib/spack/spack/cmd/compiler.py
@@ -159,7 +159,19 @@ def compiler_list(args):
     tty.msg("Available compilers")
     index = index_by(spack.compilers.all_compilers(scope=args.scope),
                      lambda c: (c.spec.name, c.operating_system, c.target))
-    ordered_sections = sorted(index.items(), key=lambda item: item[0])
+
+    # For a container, take each element which does not evaluate to false and
+    # convert it to a string. For elements which evaluate to False (e.g. None)
+    # convert them to '' (in which case it still evaluates to False but is a
+    # string type). Tuples produced by this are guaranteed to be comparable in
+    # Python 3
+    convert_str = (
+        lambda tuple_container:
+        tuple(str(x) if x else '' for x in tuple_container))
+
+    index_str_keys = list(
+        (convert_str(x), y) for x, y in index.items())
+    ordered_sections = sorted(index_str_keys, key=lambda item: item[0])
     for i, (key, compilers) in enumerate(ordered_sections):
         if i >= 1:
             print()
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index 232dfaeb4b..ec594e4088 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -12,7 +12,6 @@ import spack.repo
 
 from spack.concretize import find_spec, NoValidVersionError
 from spack.error import SpecError
-from spack.package_prefs import PackagePrefs
 from spack.spec import Spec, CompilerSpec, ConflictsInSpecError
 from spack.version import ver
 from spack.util.mock_package import MockPackageMultiRepo
@@ -103,8 +102,6 @@ def current_host(request, monkeypatch):
         monkeypatch.setattr(spack.platforms.test.Test, 'default', cpu)
         yield target
     else:
-        # There's a cache that needs to be cleared for unit tests
-        PackagePrefs._packages_config_cache = None
         with spack.config.override('packages:all', {'target': [cpu]}):
             yield target
 
@@ -112,7 +109,10 @@ def current_host(request, monkeypatch):
     spack.architecture.get_platform.cache.clear()
 
 
-@pytest.mark.usefixtures('config', 'mock_packages')
+# This must use the mutable_config fixture because the test
+# adjusting_default_target_based_on_compiler uses the current_host fixture,
+# which changes the config.
+@pytest.mark.usefixtures('mutable_config', 'mock_packages')
 class TestConcretize(object):
     def test_concretize(self, spec):
         check_concretize(spec)
diff --git a/lib/spack/spack/test/concretize_preferences.py b/lib/spack/spack/test/concretize_preferences.py
index 922d5a11d8..ca4df6700c 100644
--- a/lib/spack/spack/test/concretize_preferences.py
+++ b/lib/spack/spack/test/concretize_preferences.py
@@ -100,7 +100,7 @@ class TestConcretizePreferences(object):
         # Try the last available compiler
         compiler = str(compiler_list[-1])
         update_packages('mpileaks', 'compiler', [compiler])
-        spec = concretize('mpileaks')
+        spec = concretize('mpileaks os=redhat6 target=x86')
         assert spec.compiler == spack.spec.CompilerSpec(compiler)
 
     def test_preferred_target(self, mutable_mock_repo):
diff --git a/lib/spack/spack/test/conftest.py b/lib/spack/spack/test/conftest.py
index 736c5a5563..8eff851a37 100644
--- a/lib/spack/spack/test/conftest.py
+++ b/lib/spack/spack/test/conftest.py
@@ -423,13 +423,13 @@ def config(mock_configuration):
 
 
 @pytest.fixture(scope='function')
-def mutable_config(tmpdir_factory, configuration_dir, monkeypatch):
+def mutable_config(tmpdir_factory, configuration_dir):
     """Like config, but tests can modify the configuration."""
     mutable_dir = tmpdir_factory.mktemp('mutable_config').join('tmp')
     configuration_dir.copy(mutable_dir)
 
     cfg = spack.config.Configuration(
-        *[spack.config.ConfigScope(name, str(mutable_dir))
+        *[spack.config.ConfigScope(name, str(mutable_dir.join(name)))
           for name in ['site', 'system', 'user']])
 
     with use_configuration(cfg):
diff --git a/lib/spack/spack/test/data/config/packages.yaml b/lib/spack/spack/test/data/config/packages.yaml
index c7256ddb33..63e63e525d 100644
--- a/lib/spack/spack/test/data/config/packages.yaml
+++ b/lib/spack/spack/test/data/config/packages.yaml
@@ -1,4 +1,7 @@
 packages:
+  all:
+    providers:
+      mpi: [openmpi, mpich]
   externaltool:
     buildable: False
     paths: