From d3a1ccd2fa244224f6ffb976ae445065b0cc331d Mon Sep 17 00:00:00 2001
From: Todd Gamblin <tgamblin@llnl.gov>
Date: Fri, 13 Apr 2018 13:18:47 -0700
Subject: config: rework config system into a class instead of globals

- Current configuration code forces the config system to be initialized
  at module scope, so configs are parsed on every Spack run, essentially
  before anything else.

- We need more control over configuration init order, so move the config
  scopes into a class and reduce global state in config.py
---
 lib/spack/spack/cmd/__init__.py                |  22 +-
 lib/spack/spack/cmd/compiler.py                |  14 +-
 lib/spack/spack/cmd/compilers.py               |   4 +-
 lib/spack/spack/cmd/config.py                  |  11 +-
 lib/spack/spack/cmd/mirror.py                  |   8 +-
 lib/spack/spack/cmd/repo.py                    |   8 +-
 lib/spack/spack/compilers/__init__.py          |  21 +-
 lib/spack/spack/config.py                      | 427 ++++++++++++++-----------
 lib/spack/spack/hooks/yaml_version_check.py    |   5 +-
 lib/spack/spack/test/compilers.py              |  32 +-
 lib/spack/spack/test/concretize_preferences.py |  17 +-
 lib/spack/spack/test/config.py                 | 426 ++++++++++++------------
 lib/spack/spack/test/conftest.py               |  30 +-
 13 files changed, 555 insertions(+), 470 deletions(-)

(limited to 'lib')

diff --git a/lib/spack/spack/cmd/__init__.py b/lib/spack/spack/cmd/__init__.py
index 6c6bb8496e..6c03650fb9 100644
--- a/lib/spack/spack/cmd/__init__.py
+++ b/lib/spack/spack/cmd/__init__.py
@@ -39,15 +39,27 @@ import spack.spec
 import spack.store
 from spack.error import SpackError
 
+
 #
 # Settings for commands that modify configuration
 #
-# Commands that modify configuration by default modify the *highest*
-# priority scope.
-default_modify_scope = spack.config.highest_precedence_scope().name
+def default_modify_scope():
+    """Return the config scope that commands should modify by default.
+
+    Commands that modify configuration by default modify the *highest*
+    priority scope.
+    """
+    config = spack.config.get_configuration()
+    return config.highest_precedence_scope().name
+
+
+def default_list_scope():
+    """Return the config scope that is listed by default.
+
+    Commands that list configuration list *all* scopes (merged) by default.
+    """
+    return None
 
-# Commands that list configuration list *all* scopes by default.
-default_list_scope = None
 
 # cmd has a submodule called "list" so preserve the python list module
 python_list = list
diff --git a/lib/spack/spack/cmd/compiler.py b/lib/spack/spack/cmd/compiler.py
index 1f668b19b6..fc85f28a90 100644
--- a/lib/spack/spack/cmd/compiler.py
+++ b/lib/spack/spack/cmd/compiler.py
@@ -46,7 +46,7 @@ def setup_parser(subparser):
     sp = subparser.add_subparsers(
         metavar='SUBCOMMAND', dest='compiler_command')
 
-    scopes = spack.config.config_scopes
+    scopes = spack.config.get_configuration().scopes
 
     # Find
     find_parser = sp.add_parser(
@@ -55,7 +55,7 @@ def setup_parser(subparser):
     find_parser.add_argument('add_paths', nargs=argparse.REMAINDER)
     find_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_modify_scope,
+        default=spack.cmd.default_modify_scope(),
         help="configuration scope to modify")
 
     # Remove
@@ -67,14 +67,14 @@ def setup_parser(subparser):
     remove_parser.add_argument('compiler_spec')
     remove_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_modify_scope,
+        default=spack.cmd.default_modify_scope(),
         help="configuration scope to modify")
 
     # List
     list_parser = sp.add_parser('list', help='list available compilers')
     list_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_list_scope,
+        default=spack.cmd.default_list_scope(),
         help="configuration scope to read from")
 
     # Info
@@ -82,7 +82,7 @@ def setup_parser(subparser):
     info_parser.add_argument('compiler_spec')
     info_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_list_scope,
+        default=spack.cmd.default_list_scope(),
         help="configuration scope to read from")
 
 
@@ -113,7 +113,9 @@ def compiler_find(args):
                                                 init_config=False)
         n = len(new_compilers)
         s = 's' if n > 1 else ''
-        filename = spack.config.get_config_filename(args.scope, 'compilers')
+
+        config = spack.config.get_configuration()
+        filename = config.get_config_filename(args.scope, 'compilers')
         tty.msg("Added %d new compiler%s to %s" % (n, s, filename))
         colify(reversed(sorted(c.spec for c in new_compilers)), indent=4)
     else:
diff --git a/lib/spack/spack/cmd/compilers.py b/lib/spack/spack/cmd/compilers.py
index 9fc0fd69a3..dc3e81920e 100644
--- a/lib/spack/spack/cmd/compilers.py
+++ b/lib/spack/spack/cmd/compilers.py
@@ -22,7 +22,7 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-import spack
+import spack.config
 from spack.cmd.compiler import compiler_list
 
 description = "list available compilers"
@@ -31,7 +31,7 @@ level = "short"
 
 
 def setup_parser(subparser):
-    scopes = spack.config.config_scopes
+    scopes = spack.config.get_configuration().scopes
     subparser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
         help="configuration scope to read/modify")
diff --git a/lib/spack/spack/cmd/config.py b/lib/spack/spack/cmd/config.py
index b7536b45b7..1c5b96059c 100644
--- a/lib/spack/spack/cmd/config.py
+++ b/lib/spack/spack/cmd/config.py
@@ -32,7 +32,7 @@ level = "long"
 def setup_parser(subparser):
     # User can only choose one
     subparser.add_argument(
-        '--scope', choices=spack.config.config_scopes,
+        '--scope', choices=spack.config.get_configuration().scopes,
         metavar=spack.config.scopes_metavar,
         help="configuration scope to read/modify")
 
@@ -54,18 +54,21 @@ def setup_parser(subparser):
 
 
 def config_get(args):
-    spack.config.print_section(args.section)
+    config = spack.config.get_configuration()
+    config.print_section(args.section)
 
 
 def config_edit(args):
     if not args.scope:
         if args.section == 'compilers':
-            args.scope = spack.cmd.default_modify_scope
+            args.scope = spack.cmd.default_modify_scope()
         else:
             args.scope = 'user'
     if not args.section:
         args.section = None
-    config_file = spack.config.get_config_filename(args.scope, args.section)
+
+    config = spack.config.get_configuration()
+    config_file = config.get_config_filename(args.scope, args.section)
     spack.editor(config_file)
 
 
diff --git a/lib/spack/spack/cmd/mirror.py b/lib/spack/spack/cmd/mirror.py
index 1baf3b683e..b91531cf54 100644
--- a/lib/spack/spack/cmd/mirror.py
+++ b/lib/spack/spack/cmd/mirror.py
@@ -67,7 +67,7 @@ def setup_parser(subparser):
         const=1, default=0,
         help="only fetch one 'preferred' version per spec, not all known")
 
-    scopes = spack.config.config_scopes
+    scopes = spack.config.get_configuration().scopes
 
     # Add
     add_parser = sp.add_parser('add', help=mirror_add.__doc__)
@@ -76,7 +76,7 @@ def setup_parser(subparser):
         'url', help="url of mirror directory from 'spack mirror create'")
     add_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_modify_scope,
+        default=spack.cmd.default_modify_scope(),
         help="configuration scope to modify")
 
     # Remove
@@ -85,14 +85,14 @@ def setup_parser(subparser):
     remove_parser.add_argument('name')
     remove_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_modify_scope,
+        default=spack.cmd.default_modify_scope(),
         help="configuration scope to modify")
 
     # List
     list_parser = sp.add_parser('list', help=mirror_list.__doc__)
     list_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_list_scope,
+        default=spack.cmd.default_list_scope(),
         help="configuration scope to read from")
 
 
diff --git a/lib/spack/spack/cmd/repo.py b/lib/spack/spack/cmd/repo.py
index dab1c95612..81484f4e85 100644
--- a/lib/spack/spack/cmd/repo.py
+++ b/lib/spack/spack/cmd/repo.py
@@ -39,7 +39,7 @@ level = "long"
 
 def setup_parser(subparser):
     sp = subparser.add_subparsers(metavar='SUBCOMMAND', dest='repo_command')
-    scopes = spack.config.config_scopes
+    scopes = spack.config.get_configuration().scopes
 
     # Create
     create_parser = sp.add_parser('create', help=repo_create.__doc__)
@@ -53,7 +53,7 @@ def setup_parser(subparser):
     list_parser = sp.add_parser('list', help=repo_list.__doc__)
     list_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_list_scope,
+        default=spack.cmd.default_list_scope(),
         help="configuration scope to read from")
 
     # Add
@@ -62,7 +62,7 @@ def setup_parser(subparser):
         'path', help="path to a Spack package repository directory")
     add_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_modify_scope,
+        default=spack.cmd.default_modify_scope(),
         help="configuration scope to modify")
 
     # Remove
@@ -73,7 +73,7 @@ def setup_parser(subparser):
         help="path or namespace of a Spack package repository")
     remove_parser.add_argument(
         '--scope', choices=scopes, metavar=spack.config.scopes_metavar,
-        default=spack.cmd.default_modify_scope,
+        default=spack.cmd.default_modify_scope(),
         help="configuration scope to modify")
 
 
diff --git a/lib/spack/spack/compilers/__init__.py b/lib/spack/spack/compilers/__init__.py
index d83941c161..ed6d4c8db2 100644
--- a/lib/spack/spack/compilers/__init__.py
+++ b/lib/spack/spack/compilers/__init__.py
@@ -116,11 +116,11 @@ def get_compiler_config(scope=None, init_config=True):
 
 def compiler_config_files():
     config_files = list()
-    for scope in spack.config.config_scopes:
-        config = spack.config.get_config('compilers', scope=scope)
-        if config:
-            config_files.append(spack.config.config_scopes[scope]
-                                .get_section_filename('compilers'))
+    config = spack.config.get_configuration()
+    for scope in config.scopes:
+        compiler_config = config.get_config('compilers', scope=scope)
+        if compiler_config:
+            config_files.append(config.get_config_filename(scope, 'compilers'))
     return config_files
 
 
@@ -338,17 +338,18 @@ def compiler_for_spec(compiler_spec, arch_spec):
 
 @_auto_compiler_spec
 def get_compiler_duplicates(compiler_spec, arch_spec):
-    config_scopes = spack.config.config_scopes
-    scope_to_compilers = dict()
-    for scope in config_scopes:
+    config = spack.config.get_configuration()
+
+    scope_to_compilers = {}
+    for scope in config.scopes:
         compilers = compilers_for_spec(compiler_spec, arch_spec=arch_spec,
                                        scope=scope, use_cache=False)
         if compilers:
             scope_to_compilers[scope] = compilers
 
-    cfg_file_to_duplicates = dict()
+    cfg_file_to_duplicates = {}
     for scope, compilers in scope_to_compilers.items():
-        config_file = config_scopes[scope].get_section_filename('compilers')
+        config_file = config.get_config_filename(scope, 'compilers')
         cfg_file_to_duplicates[config_file] = compilers
 
     return cfg_file_to_duplicates
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index ba08977e72..1a32a2ddd4 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -85,23 +85,31 @@ section_schemas = {
     'config': spack.schema.config.schema,
 }
 
-#: OrderedDict of config scopes keyed by name.
-#: Later scopes will override earlier scopes.
-config_scopes = OrderedDict()
+#: Builtin paths to configuration files in Spack
+configuration_paths = (
+    # Default configuration scope is the lowest-level scope. These are
+    # versioned with Spack and can be overridden by systems, sites or users
+    ('defaults', os.path.join(spack.paths.etc_path, 'spack', 'defaults')),
+
+    # System configuration is per machine.
+    # No system-level configs should be checked into spack by default
+    ('system', os.path.join(spack.paths.system_etc_path, 'spack')),
+
+    # Site configuration is per spack instance, for sites or projects
+    # No site-level configs should be checked into spack by default.
+    ('site', os.path.join(spack.paths.etc_path, 'spack')),
+
+    # User configuration can override both spack defaults and site config
+    ('user', spack.paths.user_config_path)
+)
+
 
 #: metavar to use for commands that accept scopes
 #: this is shorter and more readable than listing all choices
 scopes_metavar = '{defaults,system,site,user}[/PLATFORM]'
 
 
-def validate_section_name(section):
-    """Exit if the section is not a valid section."""
-    if section not in section_schemas:
-        tty.die("Invalid config section: '%s'. Options are: %s"
-                % (section, " ".join(section_schemas.keys())))
-
-
-def extend_with_default(validator_class):
+def _extend_with_default(validator_class):
     """Add support for the 'default' attr for properties and patternProperties.
 
        jsonschema does not handle this out of the box -- it only
@@ -141,20 +149,8 @@ def extend_with_default(validator_class):
     })
 
 
-DefaultSettingValidator = extend_with_default(Draft4Validator)
-
-
-def validate_section(data, schema):
-    """Validate data read in from a Spack YAML file.
-
-    This leverages the line information (start_mark, end_mark) stored
-    on Spack YAML structures.
-
-    """
-    try:
-        DefaultSettingValidator(schema).validate(data)
-    except jsonschema.ValidationError as e:
-        raise ConfigFormatError(e, data)
+#: the validator we use for Spack config files
+DefaultSettingValidator = _extend_with_default(Draft4Validator)
 
 
 class ConfigScope(object):
@@ -169,13 +165,8 @@ class ConfigScope(object):
         self.path = path           # path to directory containing configs.
         self.sections = syaml.syaml_dict()  # sections read from config files.
 
-        # Register in a dict of all ConfigScopes
-        # TODO: make this cleaner.  Mocking up for testing is brittle.
-        global config_scopes
-        config_scopes[name] = self
-
     def get_section_filename(self, section):
-        validate_section_name(section)
+        _validate_section_name(section)
         return os.path.join(self.path, "%s.yaml" % section)
 
     def get_section(self, section):
@@ -192,7 +183,7 @@ class ConfigScope(object):
         try:
             mkdirp(self.path)
             with open(filename, 'w') as f:
-                validate_section(data, section_schemas[section])
+                _validate_section(data, section_schemas[section])
                 syaml.dump(data, stream=f, default_flow_style=False)
         except jsonschema.ValidationError as e:
             raise ConfigSanityError(e, data)
@@ -208,61 +199,229 @@ class ConfigScope(object):
         return '<ConfigScope: %s: %s>' % (self.name, self.path)
 
 
-#
-# Below are configuration scopes.
-#
-# Each scope can have per-platfom overrides in subdirectories of the
-# configuration directory.
-#
-_platform = spack.architecture.platform().name
+class Configuration(object):
+    """A full Spack configuration, from a hierarchy of config files.
+
+    This class makes it easy to add a new scope on top of an existing one.
+    """
+
+    def __init__(self, *scopes):
+        """Initialize a configuration with an initial list of scopes.
+
+        Args:
+            scopes (list of ConfigScope): list of scopes to add to this
+                Configuration, ordered from lowest to highest precedence
+
+        """
+        self.scopes = OrderedDict()
+        for scope in scopes:
+            self.push_scope(scope)
+
+    def push_scope(self, scope):
+        """Add a higher precedence scope to the Configuration."""
+        self.scopes[scope.name] = scope
+
+    def pop_scope(self):
+        """Remove the highest precedence scope and return it."""
+        name, scope = self.scopes.popitem(last=True)
+        return scope
 
-#: Default configuration scope is the lowest-level scope. These are
-#: versioned with Spack and can be overridden by systems, sites or users.
-_defaults_path = os.path.join(spack.paths.etc_path, 'spack', 'defaults')
-ConfigScope('defaults', _defaults_path)
-ConfigScope('defaults/%s' % _platform, os.path.join(_defaults_path, _platform))
+    def highest_precedence_scope(self):
+        """Get the scope with highest precedence (prefs will override others).
+        """
+        return list(self.scopes.values())[-1]
 
-#: System configuration is per machine.
-#: No system-level configs should be checked into spack by default
-_system_path = os.path.join(spack.paths.system_etc_path, 'spack')
-ConfigScope('system', _system_path)
-ConfigScope('system/%s' % _platform, os.path.join(_system_path, _platform))
+    def _validate_scope(self, scope):
+        """Ensure that scope is valid in this configuration.
 
-#: Site configuration is per spack instance, for sites or projects.
-#: No site-level configs should be checked into spack by default.
-_site_path = os.path.join(spack.paths.etc_path, 'spack')
-ConfigScope('site', _site_path)
-ConfigScope('site/%s' % _platform, os.path.join(_site_path, _platform))
+        This should be used by routines in ``config.py`` to validate
+        scope name arguments, and to determine a default scope where no
+        scope is specified.
 
-#: User configuration can override both spack defaults and site config.
-_user_path = spack.paths.user_config_path
-ConfigScope('user', _user_path)
-ConfigScope('user/%s' % _platform, os.path.join(_user_path, _platform))
+        Raises:
+            ValueError: if ``scope`` is not valid
 
+        Returns:
+            ConfigScope: a valid ConfigScope if ``scope`` is ``None`` or valid
+        """
+        if scope is None:
+            # default to the scope with highest precedence.
+            return self.highest_precedence_scope()
 
-def highest_precedence_scope():
-    """Get the scope with highest precedence (prefs will override others)."""
-    return list(config_scopes.values())[-1]
+        elif scope in self.scopes:
+            return self.scopes[scope]
 
+        else:
+            raise ValueError("Invalid config scope: '%s'.  Must be one of %s"
+                             % (scope, self.scopes.keys()))
+
+    def get_config_filename(self, scope, section):
+        """For some scope and section, get the name of the configuration file.
+        """
+        scope = self._validate_scope(scope)
+        return scope.get_section_filename(section)
+
+    def clear_caches(self):
+        """Clears the caches for configuration files,
+
+        This will cause files to be re-read upon the next request."""
+        for scope in self.scopes.values():
+            scope.clear()
+
+    def update_config(self, section, update_data, scope=None):
+        """Update the configuration file for a particular scope.
+
+        Overwrites contents of a section in a scope with update_data,
+        then writes out the config file.
+
+        update_data should have the top-level section name stripped off
+        (it will be re-added).  Data itself can be a list, dict, or any
+        other yaml-ish structure.
+        """
+        _validate_section_name(section)  # validate section name
+        scope = self._validate_scope(scope)  # get ConfigScope object
+
+        # read only the requested section's data.
+        scope.sections[section] = {section: update_data}
+        scope.write_section(section)
+
+    def get_config(self, section, scope=None):
+        """Get configuration settings for a section.
+
+        If ``scope`` is ``None`` or not provided, return the merged contents
+        of all of Spack's configuration scopes.  If ``scope`` is provided,
+        return only the confiugration as specified in that scope.
+
+        This off the top-level name from the YAML section.  That is, for a
+        YAML config file that looks like this::
+
+           config:
+             install_tree: $spack/opt/spack
+             module_roots:
+               lmod:   $spack/share/spack/lmod
+
+        ``get_config('config')`` will return::
+
+           { 'install_tree': '$spack/opt/spack',
+             'module_roots: {
+                 'lmod': '$spack/share/spack/lmod'
+             }
+           }
+
+        """
+        _validate_section_name(section)
+        merged_section = syaml.syaml_dict()
+
+        if scope is None:
+            scopes = self.scopes.values()
+        else:
+            scopes = [self._validate_scope(scope)]
 
-def validate_scope(scope):
-    """Ensure that scope is valid, and return a valid scope if it is None.
+        for scope in scopes:
+            # read potentially cached data from the scope.
 
-       This should be used by routines in ``config.py`` to validate
-       scope name arguments, and to determine a default scope where no
-       scope is specified.
+            data = scope.get_section(section)
+
+            # Skip empty configs
+            if not data or not isinstance(data, dict):
+                continue
+
+            if section not in data:
+                tty.warn("Skipping bad configuration file: '%s'" % scope.path)
+                continue
+
+            merged_section = _merge_yaml(merged_section, data)
+
+        # no config files -- empty config.
+        if section not in merged_section:
+            return {}
+
+        # take the top key off before returning.
+        return merged_section[section]
+
+    def __iter__(self):
+        """Iterate over scopes in this configuration."""
+        for scope in self.scopes.values():
+            yield scope
+
+    def print_section(self, section):
+        """Print a configuration to stdout."""
+        try:
+            data = syaml.syaml_dict()
+            data[section] = self.get_config(section)
+            syaml.dump(data, stream=sys.stdout, default_flow_style=False)
+        except (yaml.YAMLError, IOError):
+            raise ConfigError("Error reading configuration: %s" % section)
+
+
+def get_configuration():
+    """This constructs Spack's standard configuration scopes
+
+    This is a singleton; it constructs one instance associated with this
+    module and returns it. It is bundled inside a function so that
+    configuratoin can be initialized lazily.
+
+    Return:
+        Configuration: object for accessing spack configuration
 
     """
-    if scope is None:
-        # default to the scope with highest precedence.
-        return highest_precedence_scope()
+    global _configuration
+    if not _configuration:
+        # Each scope can have per-platfom overrides in subdirectories of the
+        # configuration directory.
+        platform = spack.architecture.platform().name
 
-    elif scope in config_scopes:
-        return config_scopes[scope]
+        scopes = []
+        for name, path in configuration_paths:
+            # add the regular scope
+            scopes.append(ConfigScope(name, path))
+
+            # add platform-specific scope
+            plat_name = '%s/%s' % (name, platform)
+            plat_path = os.path.join(path, platform)
+            scopes.append(ConfigScope(plat_name, plat_path))
+
+        _configuration = Configuration(*scopes)
+
+    return _configuration
 
-    else:
-        raise ValueError("Invalid config scope: '%s'.  Must be one of %s"
-                         % (scope, config_scopes.keys()))
+
+#: This is the global singleton configuration for Spack.
+#: TODO: consider making this NOT global and associate it with a spack instance
+_configuration = None
+
+
+#: TODO: consider getting rid of these top-level wrapper functions.
+def get_config(section, scope=None):
+    """Module-level interface for ``Configuration.get_config()``."""
+    config = get_configuration()
+    return config.get_config(section, scope)
+
+
+def update_config(section, update_data, scope=None):
+    """Module-level interface for ``Configuration.update_config()``."""
+    config = get_configuration()
+    return config.update_config(section, update_data, scope)
+
+
+def _validate_section_name(section):
+    """Exit if the section is not a valid section."""
+    if section not in section_schemas:
+        tty.die("Invalid config section: '%s'. Options are: %s"
+                % (section, " ".join(section_schemas.keys())))
+
+
+def _validate_section(data, schema):
+    """Validate data read in from a Spack YAML file.
+
+    This leverages the line information (start_mark, end_mark) stored
+    on Spack YAML structures.
+
+    """
+    try:
+        DefaultSettingValidator(schema).validate(data)
+    except jsonschema.ValidationError as e:
+        raise ConfigFormatError(e, data)
 
 
 def _read_config_file(filename, schema):
@@ -284,7 +443,7 @@ def _read_config_file(filename, schema):
             data = _mark_overrides(syaml.load(f))
 
         if data:
-            validate_section(data, schema)
+            _validate_section(data, schema)
         return data
 
     except MarkedYAMLError as e:
@@ -296,14 +455,7 @@ def _read_config_file(filename, schema):
             "Error reading configuration file %s: %s" % (filename, str(e)))
 
 
-def clear_config_caches():
-    """Clears the caches for configuration files, which will cause them
-       to be re-read upon the next request"""
-    for scope in config_scopes.values():
-        scope.clear()
-
-
-def override(string):
+def _override(string):
     """Test if a spack YAML string is an override.
 
     See ``spack_yaml`` for details.  Keys in Spack YAML can end in `::`,
@@ -363,7 +515,7 @@ def _merge_yaml(dest, source):
     # Source dict is merged into dest.
     elif they_are(dict):
         for sk, sv in iteritems(source):
-            if override(sk) or sk not in dest:
+            if _override(sk) or sk not in dest:
                 # if sk ended with ::, or if it's new, completely override
                 dest[sk] = copy.copy(sv)
             else:
@@ -376,109 +528,12 @@ def _merge_yaml(dest, source):
         return copy.copy(source)
 
 
-def get_config(section, scope=None):
-    """Get configuration settings for a section.
-
-    If ``scope`` is ``None`` or not provided, return the merged contents
-    of all of Spack's configuration scopes.  If ``scope`` is provided,
-    return only the confiugration as specified in that scope.
-
-    This off the top-level name from the YAML section.  That is, for a
-    YAML config file that looks like this::
-
-       config:
-         install_tree: $spack/opt/spack
-         module_roots:
-           lmod:   $spack/share/spack/lmod
-
-    ``get_config('config')`` will return::
-
-       { 'install_tree': '$spack/opt/spack',
-         'module_roots: {
-             'lmod': '$spack/share/spack/lmod'
-         }
-       }
-
-    """
-    validate_section_name(section)
-    merged_section = syaml.syaml_dict()
-
-    if scope is None:
-        scopes = config_scopes.values()
-    else:
-        scopes = [validate_scope(scope)]
-
-    for scope in scopes:
-        # read potentially cached data from the scope.
-
-        data = scope.get_section(section)
-
-        # Skip empty configs
-        if not data or not isinstance(data, dict):
-            continue
-
-        if section not in data:
-            tty.warn("Skipping bad configuration file: '%s'" % scope.path)
-            continue
-
-        merged_section = _merge_yaml(merged_section, data)
-
-    # no config files -- empty config.
-    if section not in merged_section:
-        return {}
-
-    # take the top key off before returning.
-    return merged_section[section]
-
-
-def get_config_filename(scope, section):
-    """For some scope and section, get the name of the configuration file"""
-    scope = validate_scope(scope)
-    return scope.get_section_filename(section)
-
-
-def update_config(section, update_data, scope=None):
-    """Update the configuration file for a particular scope.
-
-       Overwrites contents of a section in a scope with update_data,
-       then writes out the config file.
-
-       update_data should have the top-level section name stripped off
-       (it will be re-added).  Data itself can be a list, dict, or any
-       other yaml-ish structure.
-
-    """
-    validate_section_name(section)  # validate section name
-    scope = validate_scope(scope)  # get ConfigScope object from string.
-
-    # read only the requested section's data.
-    scope.sections[section] = {section: update_data}
-    scope.write_section(section)
-
-
-def print_section(section):
-    """Print a configuration to stdout."""
-    try:
-        data = syaml.syaml_dict()
-        data[section] = get_config(section)
-        syaml.dump(data, stream=sys.stdout, default_flow_style=False)
-    except (yaml.YAMLError, IOError):
-        raise ConfigError("Error reading configuration: %s" % section)
-
-
 class ConfigError(SpackError):
-    pass
+    """Superclass for all Spack config related errors."""
 
 
 class ConfigFileError(ConfigError):
-    pass
-
-
-def get_path(path, data):
-    if path:
-        return get_path(path[1:], data[path[0]])
-    else:
-        return data
+    """Issue reading or accessing a configuration file."""
 
 
 class ConfigFormatError(ConfigError):
@@ -490,6 +545,12 @@ class ConfigFormatError(ConfigError):
         parent_mark = getattr(validation_error.parent, '_start_mark', None)
         path = [str(s) for s in getattr(validation_error, 'path', None)]
 
+        def get_path(path, data):
+            if path:
+                return get_path(path[1:], data[path[0]])
+            else:
+                return data
+
         # Try really hard to get the parent (which sometimes is not
         # set) This digs it out of the validated structure if it's not
         # on the validation_error.
diff --git a/lib/spack/spack/hooks/yaml_version_check.py b/lib/spack/spack/hooks/yaml_version_check.py
index 0896f259ca..ec695319d1 100644
--- a/lib/spack/spack/hooks/yaml_version_check.py
+++ b/lib/spack/spack/hooks/yaml_version_check.py
@@ -36,8 +36,9 @@ def pre_run():
 
 
 def check_compiler_yaml_version():
-    config_scopes = spack.config.config_scopes
-    for scope in config_scopes.values():
+    config = spack.config.get_configuration()
+
+    for scope in config:
         file_name = os.path.join(scope.path, 'compilers.yaml')
         data = None
         if os.path.isfile(file_name):
diff --git a/lib/spack/spack/test/compilers.py b/lib/spack/spack/test/compilers.py
index 7875743761..2c9d68f674 100644
--- a/lib/spack/spack/test/compilers.py
+++ b/lib/spack/spack/test/compilers.py
@@ -22,7 +22,6 @@
 # License along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 ##############################################################################
-import pytest
 from six import iteritems
 
 import spack.spec
@@ -30,24 +29,23 @@ import spack.compilers as compilers
 from spack.compiler import _get_versioned_tuple
 
 
-@pytest.mark.usefixtures('config')
-class TestCompilers(object):
+def test_get_compiler_duplicates(config):
+    # In this case there is only one instance of the specified compiler in
+    # the test configuration (so it is not actually a duplicate), but the
+    # method behaves the same.
+    cfg_file_to_duplicates = compilers.get_compiler_duplicates(
+        'gcc@4.5.0', spack.spec.ArchSpec('cray-CNL-xeon'))
 
-    def test_get_compiler_duplicates(self):
-        # In this case there is only one instance of the specified compiler in
-        # the test configuration (so it is not actually a duplicate), but the
-        # method behaves the same.
-        cfg_file_to_duplicates = compilers.get_compiler_duplicates(
-            'gcc@4.5.0', spack.spec.ArchSpec('cray-CNL-xeon'))
-        assert len(cfg_file_to_duplicates) == 1
-        cfg_file, duplicates = next(iteritems(cfg_file_to_duplicates))
-        assert len(duplicates) == 1
+    assert len(cfg_file_to_duplicates) == 1
+    cfg_file, duplicates = next(iteritems(cfg_file_to_duplicates))
+    assert len(duplicates) == 1
 
-    def test_all_compilers(self):
-        all_compilers = compilers.all_compilers()
-        filtered = [x for x in all_compilers if str(x.spec) == 'clang@3.3']
-        filtered = [x for x in filtered if x.operating_system == 'SuSE11']
-        assert len(filtered) == 1
+
+def test_all_compilers(config):
+    all_compilers = compilers.all_compilers()
+    filtered = [x for x in all_compilers if str(x.spec) == 'clang@3.3']
+    filtered = [x for x in filtered if x.operating_system == 'SuSE11']
+    assert len(filtered) == 1
 
 
 def test_version_detection_is_empty():
diff --git a/lib/spack/spack/test/concretize_preferences.py b/lib/spack/spack/test/concretize_preferences.py
index 8592289f7b..5afa51cbe3 100644
--- a/lib/spack/spack/test/concretize_preferences.py
+++ b/lib/spack/spack/test/concretize_preferences.py
@@ -24,26 +24,23 @@
 ##############################################################################
 import pytest
 
-import spack
+import spack.package_prefs
 import spack.util.spack_yaml as syaml
+from spack.config import ConfigScope
 from spack.spec import Spec
-import spack.package_prefs
 
 
 @pytest.fixture()
 def concretize_scope(config, tmpdir):
     """Adds a scope for concretization preferences"""
     tmpdir.ensure_dir('concretize')
-    spack.config.ConfigScope(
-        'concretize', str(tmpdir.join('concretize'))
-    )
+    config.push_scope(
+        ConfigScope('concretize', str(tmpdir.join('concretize'))))
+
     yield
-    # This is kind of weird, but that's how config scopes are
-    # set in ConfigScope.__init__
-    spack.config.config_scopes.pop('concretize')
-    spack.package_prefs.PackagePrefs.clear_caches()
 
-    # reset provider index each time, too
+    config.pop_scope()
+    spack.package_prefs.PackagePrefs.clear_caches()
     spack.repo._provider_index = None
 
 
diff --git a/lib/spack/spack/test/config.py b/lib/spack/spack/test/config.py
index 270161cfa8..17e749d6a2 100644
--- a/lib/spack/spack/test/config.py
+++ b/lib/spack/spack/test/config.py
@@ -33,9 +33,84 @@ import yaml
 import spack.paths
 import spack.config
 from spack.util.path import canonicalize_path
-from spack.util.ordereddict import OrderedDict
 
-# Some sample compiler config data
+
+# sample config data
+config_low = {
+    'config': {
+        'install_tree': 'install_tree_path',
+        'build_stage': ['path1', 'path2', 'path3']}}
+
+config_override_all = {
+    'config:': {
+        'install_tree:': 'override_all'}}
+
+config_override_key = {
+    'config': {
+        'install_tree:': 'override_key'}}
+
+config_merge_list = {
+    'config': {
+        'build_stage': ['patha', 'pathb']}}
+
+config_override_list = {
+    'config': {
+        'build_stage:': ['patha', 'pathb']}}
+
+
+@pytest.fixture()
+def config(tmpdir):
+    """Mocks the configuration scope."""
+    real_configuration = spack.config._configuration
+    scopes = [spack.config.ConfigScope(name, str(tmpdir.join(name)))
+              for name in ['low', 'high']]
+    spack.config._configuration = spack.config.Configuration(*scopes)
+
+    yield
+
+    spack.config._configuration = real_configuration
+
+
+@pytest.fixture()
+def write_config_file(tmpdir):
+    """Returns a function that writes a config file."""
+    def _write(config, data, scope):
+        config_yaml = tmpdir.join(scope, config + '.yaml')
+        config_yaml.ensure()
+        with config_yaml.open('w') as f:
+            yaml.dump(data, f)
+    return _write
+
+
+def check_compiler_config(comps, *compiler_names):
+    """Check that named compilers in comps match Spack's config."""
+    config = spack.config.get_config('compilers')
+    compiler_list = ['cc', 'cxx', 'f77', 'fc']
+    flag_list = ['cflags', 'cxxflags', 'fflags', 'cppflags',
+                 'ldflags', 'ldlibs']
+    param_list = ['modules', 'paths', 'spec', 'operating_system']
+    for compiler in config:
+        conf = compiler['compiler']
+        if conf['spec'] in compiler_names:
+            comp = next((c['compiler'] for c in comps if
+                         c['compiler']['spec'] == conf['spec']), None)
+            if not comp:
+                raise ValueError('Bad config spec')
+            for p in param_list:
+                assert conf[p] == comp[p]
+            for f in flag_list:
+                expected = comp.get('flags', {}).get(f, None)
+                actual = conf.get('flags', {}).get(f, None)
+                assert expected == actual
+            for c in compiler_list:
+                expected = comp['paths'][c]
+                actual = conf['paths'][c]
+                assert expected == actual
+
+
+#
+# Some sample compiler config data and tests.
+#
 a_comps = {
     'compilers': [
         {'compiler': {
@@ -140,32 +215,110 @@ b_comps = {
     ]
 }
 
-# Some Sample repo data
+
+@pytest.fixture()
+def compiler_specs():
+    """Returns a couple of compiler specs needed for the tests"""
+    a = [ac['compiler']['spec'] for ac in a_comps['compilers']]
+    b = [bc['compiler']['spec'] for bc in b_comps['compilers']]
+    CompilerSpecs = collections.namedtuple('CompilerSpecs', ['a', 'b'])
+    return CompilerSpecs(a=a, b=b)
+
+
+def test_write_key_in_memory(config, compiler_specs):
+    # Write b_comps "on top of" a_comps.
+    spack.config.update_config(
+        'compilers', a_comps['compilers'], scope='low'
+    )
+    spack.config.update_config(
+        'compilers', b_comps['compilers'], scope='high'
+    )
+
+    # Make sure the config looks how we expect.
+    check_compiler_config(a_comps['compilers'], *compiler_specs.a)
+    check_compiler_config(b_comps['compilers'], *compiler_specs.b)
+
+
+def test_write_key_to_disk(config, compiler_specs):
+    # Write b_comps "on top of" a_comps.
+    spack.config.update_config(
+        'compilers', a_comps['compilers'], scope='low'
+    )
+    spack.config.update_config(
+        'compilers', b_comps['compilers'], scope='high'
+    )
+
+    # Clear caches so we're forced to read from disk.
+    spack.config.get_configuration().clear_caches()
+
+    # Same check again, to ensure consistency.
+    check_compiler_config(a_comps['compilers'], *compiler_specs.a)
+    check_compiler_config(b_comps['compilers'], *compiler_specs.b)
+
+
+def test_write_to_same_priority_file(config, compiler_specs):
+    # Write b_comps in the same file as a_comps.
+    spack.config.update_config(
+        'compilers', a_comps['compilers'], scope='low'
+    )
+    spack.config.update_config(
+        'compilers', b_comps['compilers'], scope='low'
+    )
+
+    # Clear caches so we're forced to read from disk.
+    spack.config.get_configuration().clear_caches()
+
+    # Same check again, to ensure consistency.
+    check_compiler_config(a_comps['compilers'], *compiler_specs.a)
+    check_compiler_config(b_comps['compilers'], *compiler_specs.b)
+
+
+#
+# Sample repo data and tests
+#
 repos_low = {'repos': ["/some/path"]}
 repos_high = {'repos': ["/some/other/path"]}
 
 
-# sample config data
-config_low = {
-    'config': {
-        'install_tree': 'install_tree_path',
-        'build_stage': ['path1', 'path2', 'path3']}}
+# repos
+def test_write_list_in_memory(config):
+    spack.config.update_config('repos', repos_low['repos'], scope='low')
+    spack.config.update_config('repos', repos_high['repos'], scope='high')
 
-config_override_all = {
-    'config:': {
-        'install_tree:': 'override_all'}}
+    config = spack.config.get_config('repos')
+    assert config == repos_high['repos'] + repos_low['repos']
 
-config_override_key = {
-    'config': {
-        'install_tree:': 'override_key'}}
 
-config_merge_list = {
-    'config': {
-        'build_stage': ['patha', 'pathb']}}
+def test_substitute_config_variables(config):
+    prefix = spack.paths.prefix.lstrip('/')
 
-config_override_list = {
-    'config': {
-        'build_stage:': ['patha', 'pathb']}}
+    assert os.path.join(
+        '/foo/bar/baz', prefix
+    ) == canonicalize_path('/foo/bar/baz/$spack')
+
+    assert os.path.join(
+        spack.paths.prefix, 'foo/bar/baz'
+    ) == canonicalize_path('$spack/foo/bar/baz/')
+
+    assert os.path.join(
+        '/foo/bar/baz', prefix, 'foo/bar/baz'
+    ) == canonicalize_path('/foo/bar/baz/$spack/foo/bar/baz/')
+
+    assert os.path.join(
+        '/foo/bar/baz', prefix
+    ) == canonicalize_path('/foo/bar/baz/${spack}')
+
+    assert os.path.join(
+        spack.paths.prefix, 'foo/bar/baz'
+    ) == canonicalize_path('${spack}/foo/bar/baz/')
+
+    assert os.path.join(
+        '/foo/bar/baz', prefix, 'foo/bar/baz'
+    ) == canonicalize_path('/foo/bar/baz/${spack}/foo/bar/baz/')
+
+    assert os.path.join(
+        '/foo/bar/baz', prefix, 'foo/bar/baz'
+    ) != canonicalize_path('/foo/bar/baz/${spack/foo/bar/baz/')
 
 
 packages_merge_low = {
@@ -212,208 +365,59 @@ def test_merge_with_defaults(config, write_config_file):
     assert cfg['baz']['version'] == ['c']
 
 
-def check_compiler_config(comps, *compiler_names):
-    """Check that named compilers in comps match Spack's config."""
-    config = spack.config.get_config('compilers')
-    compiler_list = ['cc', 'cxx', 'f77', 'fc']
-    flag_list = ['cflags', 'cxxflags', 'fflags', 'cppflags',
-                 'ldflags', 'ldlibs']
-    param_list = ['modules', 'paths', 'spec', 'operating_system']
-    for compiler in config:
-        conf = compiler['compiler']
-        if conf['spec'] in compiler_names:
-            comp = next((c['compiler'] for c in comps if
-                         c['compiler']['spec'] == conf['spec']), None)
-            if not comp:
-                raise ValueError('Bad config spec')
-            for p in param_list:
-                assert conf[p] == comp[p]
-            for f in flag_list:
-                expected = comp.get('flags', {}).get(f, None)
-                actual = conf.get('flags', {}).get(f, None)
-                assert expected == actual
-            for c in compiler_list:
-                expected = comp['paths'][c]
-                actual = conf['paths'][c]
-                assert expected == actual
+def test_substitute_user(config):
+    user = getpass.getuser()
+    assert '/foo/bar/' + user + '/baz' == canonicalize_path(
+        '/foo/bar/$user/baz'
+    )
 
 
-@pytest.fixture()
-def config(tmpdir):
-    """Mocks the configuration scope."""
-    spack.config.clear_config_caches()
-    real_scope = spack.config.config_scopes
-    spack.config.config_scopes = OrderedDict()
-    for priority in ['low', 'high']:
-        spack.config.ConfigScope(priority, str(tmpdir.join(priority)))
-    Config = collections.namedtuple('Config', ['real', 'mock'])
-    yield Config(real=real_scope, mock=spack.config.config_scopes)
-    spack.config.config_scopes = real_scope
-    spack.config.clear_config_caches()
+def test_substitute_tempdir(config):
+    tempdir = tempfile.gettempdir()
+    assert tempdir == canonicalize_path('$tempdir')
+    assert tempdir + '/foo/bar/baz' == canonicalize_path(
+        '$tempdir/foo/bar/baz'
+    )
 
 
-@pytest.fixture()
-def write_config_file(tmpdir):
-    """Returns a function that writes a config file."""
-    def _write(config, data, scope):
-        config_yaml = tmpdir.join(scope, config + '.yaml')
-        config_yaml.ensure()
-        with config_yaml.open('w') as f:
-            yaml.dump(data, f)
-    return _write
+def test_read_config(config, write_config_file):
+    write_config_file('config', config_low, 'low')
+    assert spack.config.get_config('config') == config_low['config']
 
 
-@pytest.fixture()
-def compiler_specs():
-    """Returns a couple of compiler specs needed for the tests"""
-    a = [ac['compiler']['spec'] for ac in a_comps['compilers']]
-    b = [bc['compiler']['spec'] for bc in b_comps['compilers']]
-    CompilerSpecs = collections.namedtuple('CompilerSpecs', ['a', 'b'])
-    return CompilerSpecs(a=a, b=b)
+def test_read_config_override_all(config, write_config_file):
+    write_config_file('config', config_low, 'low')
+    write_config_file('config', config_override_all, 'high')
+    assert spack.config.get_config('config') == {
+        'install_tree': 'override_all'
+    }
 
 
-@pytest.mark.usefixtures('config')
-class TestConfig(object):
-
-    def test_write_list_in_memory(self):
-        spack.config.update_config('repos', repos_low['repos'], scope='low')
-        spack.config.update_config('repos', repos_high['repos'], scope='high')
-
-        config = spack.config.get_config('repos')
-        assert config == repos_high['repos'] + repos_low['repos']
-
-    def test_write_key_in_memory(self, compiler_specs):
-        # Write b_comps "on top of" a_comps.
-        spack.config.update_config(
-            'compilers', a_comps['compilers'], scope='low'
-        )
-        spack.config.update_config(
-            'compilers', b_comps['compilers'], scope='high'
-        )
-        # Make sure the config looks how we expect.
-        check_compiler_config(a_comps['compilers'], *compiler_specs.a)
-        check_compiler_config(b_comps['compilers'], *compiler_specs.b)
-
-    def test_write_key_to_disk(self, compiler_specs):
-        # Write b_comps "on top of" a_comps.
-        spack.config.update_config(
-            'compilers', a_comps['compilers'], scope='low'
-        )
-        spack.config.update_config(
-            'compilers', b_comps['compilers'], scope='high'
-        )
-        # Clear caches so we're forced to read from disk.
-        spack.config.clear_config_caches()
-        # Same check again, to ensure consistency.
-        check_compiler_config(a_comps['compilers'], *compiler_specs.a)
-        check_compiler_config(b_comps['compilers'], *compiler_specs.b)
-
-    def test_write_to_same_priority_file(self, compiler_specs):
-        # Write b_comps in the same file as a_comps.
-        spack.config.update_config(
-            'compilers', a_comps['compilers'], scope='low'
-        )
-        spack.config.update_config(
-            'compilers', b_comps['compilers'], scope='low'
-        )
-        # Clear caches so we're forced to read from disk.
-        spack.config.clear_config_caches()
-        # Same check again, to ensure consistency.
-        check_compiler_config(a_comps['compilers'], *compiler_specs.a)
-        check_compiler_config(b_comps['compilers'], *compiler_specs.b)
-
-    def check_canonical(self, var, expected):
-        """Ensure that <expected> is substituted properly for <var> in strings
-           containing <var> in various positions."""
-        path = '/foo/bar/baz'
-
-        self.assertEqual(canonicalize_path(var + path),
-                         expected + path)
-
-        self.assertEqual(canonicalize_path(path + var),
-                         path + '/' + expected)
-
-        self.assertEqual(canonicalize_path(path + var + path),
-                         expected + path)
-
-    def test_substitute_config_variables(self):
-        prefix = spack.paths.prefix.lstrip('/')
-
-        assert os.path.join(
-            '/foo/bar/baz', prefix
-        ) == canonicalize_path('/foo/bar/baz/$spack')
-
-        assert os.path.join(
-            spack.paths.prefix, 'foo/bar/baz'
-        ) == canonicalize_path('$spack/foo/bar/baz/')
-
-        assert os.path.join(
-            '/foo/bar/baz', prefix, 'foo/bar/baz'
-        ) == canonicalize_path('/foo/bar/baz/$spack/foo/bar/baz/')
-
-        assert os.path.join(
-            '/foo/bar/baz', prefix
-        ) == canonicalize_path('/foo/bar/baz/${spack}')
-
-        assert os.path.join(
-            spack.paths.prefix, 'foo/bar/baz'
-        ) == canonicalize_path('${spack}/foo/bar/baz/')
-
-        assert os.path.join(
-            '/foo/bar/baz', prefix, 'foo/bar/baz'
-        ) == canonicalize_path('/foo/bar/baz/${spack}/foo/bar/baz/')
-
-        assert os.path.join(
-            '/foo/bar/baz', prefix, 'foo/bar/baz'
-        ) != canonicalize_path('/foo/bar/baz/${spack/foo/bar/baz/')
-
-    def test_substitute_user(self):
-        user = getpass.getuser()
-        assert '/foo/bar/' + user + '/baz' == canonicalize_path(
-            '/foo/bar/$user/baz'
-        )
-
-    def test_substitute_tempdir(self):
-        tempdir = tempfile.gettempdir()
-        assert tempdir == canonicalize_path('$tempdir')
-        assert tempdir + '/foo/bar/baz' == canonicalize_path(
-            '$tempdir/foo/bar/baz'
-        )
-
-    def test_read_config(self, write_config_file):
-        write_config_file('config', config_low, 'low')
-        assert spack.config.get_config('config') == config_low['config']
-
-    def test_read_config_override_all(self, write_config_file):
-        write_config_file('config', config_low, 'low')
-        write_config_file('config', config_override_all, 'high')
-        assert spack.config.get_config('config') == {
-            'install_tree': 'override_all'
-        }
+def test_read_config_override_key(config, write_config_file):
+    write_config_file('config', config_low, 'low')
+    write_config_file('config', config_override_key, 'high')
+    assert spack.config.get_config('config') == {
+        'install_tree': 'override_key',
+        'build_stage': ['path1', 'path2', 'path3']
+    }
 
-    def test_read_config_override_key(self, write_config_file):
-        write_config_file('config', config_low, 'low')
-        write_config_file('config', config_override_key, 'high')
-        assert spack.config.get_config('config') == {
-            'install_tree': 'override_key',
-            'build_stage': ['path1', 'path2', 'path3']
-        }
 
-    def test_read_config_merge_list(self, write_config_file):
-        write_config_file('config', config_low, 'low')
-        write_config_file('config', config_merge_list, 'high')
-        assert spack.config.get_config('config') == {
-            'install_tree': 'install_tree_path',
-            'build_stage': ['patha', 'pathb', 'path1', 'path2', 'path3']
-        }
+def test_read_config_merge_list(config, write_config_file):
+    write_config_file('config', config_low, 'low')
+    write_config_file('config', config_merge_list, 'high')
+    assert spack.config.get_config('config') == {
+        'install_tree': 'install_tree_path',
+        'build_stage': ['patha', 'pathb', 'path1', 'path2', 'path3']
+    }
 
-    def test_read_config_override_list(self, write_config_file):
-        write_config_file('config', config_low, 'low')
-        write_config_file('config', config_override_list, 'high')
-        assert spack.config.get_config('config') == {
-            'install_tree': 'install_tree_path',
-            'build_stage': ['patha', 'pathb']
-        }
+
+def test_read_config_override_list(config, write_config_file):
+    write_config_file('config', config_low, 'low')
+    write_config_file('config', config_override_list, 'high')
+    assert spack.config.get_config('config') == {
+        'install_tree': 'install_tree_path',
+        'build_stage': ['patha', 'pathb']
+    }
 
 
 def test_keys_are_ordered():
diff --git a/lib/spack/spack/test/conftest.py b/lib/spack/spack/test/conftest.py
index 311c57a4ce..997cdb724c 100644
--- a/lib/spack/spack/test/conftest.py
+++ b/lib/spack/spack/test/conftest.py
@@ -216,17 +216,21 @@ def configuration_dir(tmpdir_factory, linux_os):
     directory path.
     """
     tmpdir = tmpdir_factory.mktemp('configurations')
+
     # Name of the yaml files in the test/data folder
     test_path = py.path.local(spack.paths.test_path)
     compilers_yaml = test_path.join('data', 'compilers.yaml')
     packages_yaml = test_path.join('data', 'packages.yaml')
     config_yaml = test_path.join('data', 'config.yaml')
+
     # Create temporary 'site' and 'user' folders
     tmpdir.ensure('site', dir=True)
     tmpdir.ensure('user', dir=True)
+
     # Copy the configurations that don't need further work
     packages_yaml.copy(tmpdir.join('site', 'packages.yaml'))
     config_yaml.copy(tmpdir.join('site', 'config.yaml'))
+
     # Write the one that needs modifications
     content = ''.join(compilers_yaml.read()).format(linux_os)
     t = tmpdir.join('site', 'compilers.yaml')
@@ -239,18 +243,20 @@ def config(configuration_dir):
     """Hooks the mock configuration files into spack.config"""
     # Set up a mock config scope
     spack.package_prefs.PackagePrefs.clear_caches()
-    spack.config.clear_config_caches()
-    real_scope = spack.config.config_scopes
-    spack.config.config_scopes = spack.util.ordereddict.OrderedDict()
-    spack.config.ConfigScope('site', str(configuration_dir.join('site')))
-    spack.config.ConfigScope('system', str(configuration_dir.join('system')))
-    spack.config.ConfigScope('user', str(configuration_dir.join('user')))
-    Config = collections.namedtuple('Config', ['real', 'mock'])
-
-    yield Config(real=real_scope, mock=spack.config.config_scopes)
-
-    spack.config.config_scopes = real_scope
-    spack.config.clear_config_caches()
+
+    real_configuration = spack.config._configuration
+
+    print real_configuration
+
+    scopes = [
+        spack.config.ConfigScope(name, str(configuration_dir.join(name)))
+        for name in ['site', 'system', 'user']]
+    config = spack.config.Configuration(*scopes)
+    spack.config._configuration = config
+
+    yield config
+
+    spack.config._configuration = real_configuration
     spack.package_prefs.PackagePrefs.clear_caches()
 
 
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