Spec constraints and normalization now work.

- Specs can be "constrained" by other specs, throw exceptions when constraint
  can't be satisfied.

- Normalize will put a spec in DAG form and merge all package constraints with
  the spec.

- Ready to add concretization policies for abstract specs now.

17 files changed, 473 insertions, 191 deletions

diff --git a/lib/spack/spack/cmd/spec.py b/lib/spack/spack/cmd/spec.py
index 5c389bd04a..f87e94dae6 100644
--- a/lib/spack/spack/cmd/spec.py
+++ b/lib/spack/spack/cmd/spec.py
@@ -12,6 +12,5 @@ def setup_parser(subparser):
 def spec(parser, args):
     specs = spack.cmd.parse_specs(args.specs)
     for spec in specs:
-        print spec.colorized()
-        print "  --> ", spec.concretized().colorized()
-        print spec.concretized().concrete()
+        spec.normalize()
+        print spec.tree()
diff --git a/lib/spack/spack/globals.py b/lib/spack/spack/globals.py
index a9fa25c784..3b2359e21d 100644
--- a/lib/spack/spack/globals.py
+++ b/lib/spack/spack/globals.py
@@ -32,7 +32,7 @@ install_path   = new_path(prefix, "opt")
 install_layout = DefaultDirectoryLayout(install_path)
 
 # Version information
-spack_version = Version("0.2")
+spack_version = Version("0.5")
 
 # User's editor from the environment
 editor = Executable(os.environ.get("EDITOR", ""))
diff --git a/lib/spack/spack/package.py b/lib/spack/spack/package.py
index 7e11c92d2d..9eece8afcf 100644
--- a/lib/spack/spack/package.py
+++ b/lib/spack/spack/package.py
@@ -381,7 +381,7 @@ class Package(object):
     @property
     @memoized
     def all_dependencies(self):
-        """Set of all transitive dependencies of this package."""
+        """Dict(str -> Package) of all transitive dependencies of this package."""
         all_deps = set(self.dependencies)
         for dep in self.dependencies:
             dep_pkg = packages.get(dep.name)
diff --git a/lib/spack/spack/packages/__init__.py b/lib/spack/spack/packages/__init__.py
index b9987aa040..6d515274b6 100644
--- a/lib/spack/spack/packages/__init__.py
+++ b/lib/spack/spack/packages/__init__.py
@@ -9,6 +9,7 @@ import spack
 import spack.error
 import spack.spec
 from spack.util.filesystem import new_path
+from spack.util.lang import list_modules
 import spack.arch as arch
 
 # Valid package names can contain '-' but can't start with it.
@@ -19,13 +20,12 @@ invalid_package_re = r'[_-][_-]+'
 
 instances = {}
 
-def get(spec):
-    spec = spack.spec.make_spec(spec)
-    if not spec in instances:
-        package_class = get_class_for_package_name(spec.name)
-        instances[spec] = package_class(spec)
+def get(pkg_name):
+    if not pkg_name in instances:
+        package_class = get_class_for_package_name(pkg_name)
+        instances[pkg_name] = package_class(pkg_name)
 
-    return instances[spec]
+    return instances[pkg_name]
 
 
 def valid_package_name(pkg_name):
diff --git a/lib/spack/spack/packages/callpath.py b/lib/spack/spack/packages/callpath.py
new file mode 100644
index 0000000000..958960e0ab
--- /dev/null
+++ b/lib/spack/spack/packages/callpath.py
@@ -0,0 +1,14 @@
+from spack import *
+
+class Callpath(Package):
+    homepage = "https://github.com/tgamblin/callpath"
+    url      = "http://github.com/tgamblin/callpath-0.2.tar.gz"
+    md5      = "foobarbaz"
+
+    depends_on("dyninst")
+    depends_on("mpich")
+
+    def install(self, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")
diff --git a/lib/spack/spack/packages/dyninst.py b/lib/spack/spack/packages/dyninst.py
new file mode 100644
index 0000000000..f550cde54f
--- /dev/null
+++ b/lib/spack/spack/packages/dyninst.py
@@ -0,0 +1,14 @@
+from spack import *
+
+class Dyninst(Package):
+    homepage = "https://paradyn.org"
+    url      = "http://www.dyninst.org/sites/default/files/downloads/dyninst/8.1.2/DyninstAPI-8.1.2.tgz"
+    md5      = "bf03b33375afa66fe0efa46ce3f4b17a"
+
+    depends_on("libelf")
+    depends_on("libdwarf")
+
+    def install(self, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")
diff --git a/lib/spack/spack/packages/libdwarf.py b/lib/spack/spack/packages/libdwarf.py
index bae701b38b..edaba6a216 100644
--- a/lib/spack/spack/packages/libdwarf.py
+++ b/lib/spack/spack/packages/libdwarf.py
@@ -11,7 +11,7 @@ class Libdwarf(Package):
 
     list_url = "http://reality.sgiweb.org/davea/dwarf.html"
 
-    depends_on("libelf")
+    depends_on("libelf@0:1")
 
 
     def clean(self):
diff --git a/lib/spack/spack/packages/mpich.py b/lib/spack/spack/packages/mpich.py
new file mode 100644
index 0000000000..d8cd67d528
--- /dev/null
+++ b/lib/spack/spack/packages/mpich.py
@@ -0,0 +1,11 @@
+from spack import *
+
+class Mpich(Package):
+    homepage = "http://www.mpich.org"
+    url      = "http://www.mpich.org/static/downloads/3.0.4/mpich-3.0.4.tar.gz"
+    md5      = "9c5d5d4fe1e17dd12153f40bc5b6dbc0"
+
+    def install(self, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")
diff --git a/lib/spack/spack/packages/mpileaks.py b/lib/spack/spack/packages/mpileaks.py
new file mode 100644
index 0000000000..224557cc52
--- /dev/null
+++ b/lib/spack/spack/packages/mpileaks.py
@@ -0,0 +1,14 @@
+from spack import *
+
+class Mpileaks(Package):
+    homepage = "http://www.llnl.gov"
+    url      = "http://www.llnl.gov/mpileaks-1.0.tar.gz"
+    md5      = "foobarbaz"
+
+    depends_on("mpich")
+    depends_on("callpath")
+
+    def install(self, prefix):
+        configure("--prefix=%s" % prefix)
+        make()
+        make("install")
diff --git a/lib/spack/spack/parse.py b/lib/spack/spack/parse.py
index 5bcdced6ca..5431aa454d 100644
--- a/lib/spack/spack/parse.py
+++ b/lib/spack/spack/parse.py
@@ -1,20 +1,6 @@
 import re
-import spack.error as err
 import itertools
-
-
-class ParseError(err.SpackError):
-    """Raised when we don't hit an error while parsing."""
-    def __init__(self, message, string, pos):
-        super(ParseError, self).__init__(message)
-        self.string = string
-        self.pos = pos
-
-
-class LexError(ParseError):
-    """Raised when we don't know how to lex something."""
-    def __init__(self, message, string, pos):
-        super(LexError, self).__init__(message, string, pos)
+import spack.error
 
 
 class Token:
@@ -109,3 +95,17 @@ class Parser(object):
         self.text = text
         self.push_tokens(self.lexer.lex(text))
         return self.do_parse()
+
+
+class ParseError(spack.error.SpackError):
+    """Raised when we don't hit an error while parsing."""
+    def __init__(self, message, string, pos):
+        super(ParseError, self).__init__(message)
+        self.string = string
+        self.pos = pos
+
+
+class LexError(ParseError):
+    """Raised when we don't know how to lex something."""
+    def __init__(self, message, string, pos):
+        super(LexError, self).__init__(message, string, pos)
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index d7998a8fb1..edc97c7c3b 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -62,7 +62,6 @@ specs to avoid ambiguity.  Both are provided because ~ can cause shell
 expansion when it is the first character in an id typed on the command line.
 """
 import sys
-from functools import total_ordering
 from StringIO import StringIO
 
 import tty
@@ -72,8 +71,11 @@ import spack.compilers
 import spack.compilers.gcc
 import spack.packages as packages
 import spack.arch as arch
+
 from spack.version import *
 from spack.color import *
+from spack.util.lang import *
+from spack.util.string import *
 
 """This map determines the coloring of specs when using color output.
    We make the fields different colors to enhance readability.
@@ -109,6 +111,7 @@ def colorize_spec(spec):
     return colorize(re.sub(separators, insert_color(), str(spec)) + '@.')
 
 
+@key_ordering
 class Compiler(object):
     """The Compiler field represents the compiler or range of compiler
        versions that a package should be built with.  Compilers have a
@@ -128,6 +131,19 @@ class Compiler(object):
         self.versions.add(version)
 
 
+    def satisfies(self, other):
+        return (self.name == other.name and
+                self.versions.overlaps(other.versions))
+
+
+    def constrain(self, other):
+        if not self.satisfies(other.compiler):
+            raise UnsatisfiableCompilerSpecError(
+                "%s does not satisfy %s" % (self.compiler, other.compiler))
+
+        self.versions.intersect(other.versions)
+
+
     @property
     def concrete(self):
         return self.versions.concrete
@@ -163,16 +179,8 @@ class Compiler(object):
         return clone
 
 
-    def __eq__(self, other):
-        return (self.name, self.versions) == (other.name, other.versions)
-
-
-    def __ne__(self, other):
-        return not (self == other)
-
-
-    def __hash__(self):
-        return hash((self.name, self.versions))
+    def _cmp_key(self):
+        return (self.name, self.versions)
 
 
     def __str__(self):
@@ -183,7 +191,7 @@ class Compiler(object):
         return out
 
 
-@total_ordering
+@key_ordering
 class Variant(object):
     """Variants are named, build-time options for a package.  Names depend
        on the particular package being built, and each named variant can
@@ -194,67 +202,21 @@ class Variant(object):
         self.enabled = enabled
 
 
-    def __eq__(self, other):
-        return self.name == other.name and self.enabled == other.enabled
-
-
-    def __ne__(self, other):
-        return not (self == other)
-
-
-    @property
-    def tuple(self):
+    def _cmp_key(self):
         return (self.name, self.enabled)
 
 
-    def __hash__(self):
-        return hash(self.tuple)
-
-
-    def __lt__(self, other):
-        return self.tuple < other.tuple
-
-
     def __str__(self):
         out = '+' if self.enabled else '~'
         return out + self.name
 
 
-
-@total_ordering
-class HashableMap(dict):
-    """This is a hashable, comparable dictionary.  Hash is performed on
-       a tuple of the values in the dictionary."""
-    def __eq__(self, other):
-        return (len(self) == len(other) and
-                sorted(self.values()) == sorted(other.values()))
-
-
-    def __ne__(self, other):
-        return not (self == other)
-
-
-    def __lt__(self, other):
-        return tuple(sorted(self.values())) < tuple(sorted(other.values()))
-
-
-    def __hash__(self):
-        return hash(tuple(sorted(self.values())))
-
-
-    def copy(self):
-        """Type-agnostic clone method.  Preserves subclass type."""
-        # Construct a new dict of my type
-        T = type(self)
-        clone = T()
-
-        # Copy everything from this dict into it.
-        for key in self:
-            clone[key] = self[key]
-        return clone
+class VariantMap(HashableMap):
+    def satisfies(self, other):
+        return all(self[key].enabled == other[key].enabled
+                   for key in other if key in self)
 
 
-class VariantMap(HashableMap):
     def __str__(self):
         sorted_keys = sorted(self.keys())
         return ''.join(str(self[key]) for key in sorted_keys)
@@ -268,13 +230,18 @@ class DependencyMap(HashableMap):
         return all(d.concrete for d in self.values())
 
 
+    def satisfies(self, other):
+        return all(self[name].satisfies(other[name]) for name in self
+                   if name in other)
+
+
     def __str__(self):
-        sorted_keys = sorted(self.keys())
+        sorted_dep_names = sorted(self.keys())
         return ''.join(
-            ["^" + str(self[name]) for name in sorted_keys])
+            ["^" + str(self[name]) for name in sorted_dep_names])
 
 
-@total_ordering
+@key_ordering
 class Spec(object):
     def __init__(self, name):
         self.name = name
@@ -322,11 +289,11 @@ class Spec(object):
 
     @property
     def concrete(self):
-        return (self.versions.concrete
-                # TODO: support variants
-                and self.architecture
-                and self.compiler and self.compiler.concrete
-                and self.dependencies.concrete)
+        return bool(self.versions.concrete
+                    # TODO: support variants
+                    and self.architecture
+                    and self.compiler and self.compiler.concrete
+                    and self.dependencies.concrete)
 
 
     def _concretize(self):
@@ -349,7 +316,7 @@ class Spec(object):
         """
         # TODO: modularize the process of selecting concrete versions.
         # There should be a set of user-configurable policies for these decisions.
-        self.check_sanity()
+        self.validate()
 
         # take the system's architecture for starters
         if not self.architecture:
@@ -370,60 +337,118 @@ class Spec(object):
         # Ensure dependencies have right versions
 
 
+    @property
+    def traverse_deps(self, visited=None):
+        """Yields dependencies in depth-first order"""
+        if not visited:
+            visited = set()
+
+        for name in sorted(self.dependencies.keys()):
+            dep = dependencies[name]
+            if dep in visited:
+                continue
 
-    def check_sanity(self):
-        """Check names of packages and dependency validity."""
-        self.check_package_name_sanity()
-        self.check_dependency_sanity()
-        self.check_dependence_constraint_sanity()
-
+            for d in dep.traverse_deps(seen):
+                yield d
+            yield dep
 
-    def check_package_name_sanity(self):
-        """Ensure that all packages mentioned in the spec exist."""
-        packages.get(self.name)
-        for dep in self.dependencies.values():
-            packages.get(dep.name)
 
+    def _normalize_helper(self, visited, spec_deps):
+        """Recursive helper function for _normalize."""
+        if self.name in visited:
+            return
+        visited.add(self.name)
 
-    def check_dependency_sanity(self):
-        """Ensure that dependencies specified on the spec are actual
-           dependencies of the package it represents.
-        """
+        # Combine constraints from package dependencies with
+        # information in this spec's dependencies.
         pkg = packages.get(self.name)
-        dep_names = set(dep.name for dep in pkg.all_dependencies)
-        invalid_dependencies = [d.name for d in self.dependencies.values()
-                                if d.name not in dep_names]
-        if invalid_dependencies:
+        for pkg_dep in pkg.dependencies:
+            name = pkg_dep.name
+
+            if name not in spec_deps:
+                # Clone the spec from the package
+                spec_deps[name] = pkg_dep.copy()
+
+            try:
+                # intersect package information with spec info
+                spec_deps[name].constrain(pkg_dep)
+            except UnsatisfiableSpecError, e:
+                error_type = type(e)
+                raise error_type(
+                    "Violated depends_on constraint from package %s: %s"
+                    % (self.name, e.message))
+
+            # Add merged spec to my deps and recurse
+            self.dependencies[name] = spec_deps[name]
+            self.dependencies[name]._normalize_helper(visited, spec_deps)
+
+
+    def normalize(self):
+        if any(dep.dependencies for dep in self.dependencies.values()):
+            raise SpecError("Spec has already been normalized.")
+
+        self.validate_package_names()
+
+        spec_deps = self.dependencies
+        self.dependencies = DependencyMap()
+
+        visited = set()
+        self._normalize_helper(visited, spec_deps)
+
+        # If there are deps specified but not visited, they're not
+        # actually deps of this package.  Raise an error.
+        extra = set(spec_deps.viewkeys()).difference(visited)
+        if extra:
             raise InvalidDependencyException(
-                "The packages (%s) are not dependencies of %s" %
-                (','.join(invalid_dependencies), self.name))
+                self.name + " does not depend on " + comma_or(extra))
 
 
-    def check_dependence_constraint_sanity(self):
-        """Ensure that package's dependencies have consistent constraints on
-           their dependencies.
-        """
-        pkg = packages.get(self.name)
-        specs = {}
-        for spec in pkg.all_dependencies:
-            if not spec.name in specs:
-                specs[spec.name] = spec
-                continue
+    def validate_package_names(self):
+        for name in self.dependencies:
+            packages.get(name)
 
-            merged = specs[spec.name]
 
-            # Specs in deps can't be disjoint.
-            if not spec.versions.overlaps(merged.versions):
-                raise InvalidConstraintException(
-                    "One package %s, version constraint %s conflicts with %s"
-                    % (pkg.name, spec.versions, merged.versions))
+    def constrain(self, other):
+        if not self.versions.overlaps(other.versions):
+            raise UnsatisfiableVersionSpecError(
+                "%s does not satisfy %s" % (self.versions, other.versions))
 
+        conflicting_variants = [
+            v for v in other.variants if v in self.variants and
+            self.variants[v].enabled != other.variants[v].enabled]
 
-    def merge(self, other):
-        """Considering these specs as constraints, attempt to merge.
-           Raise an exception if specs are disjoint.
-        """
-        pass
+        if conflicting_variants:
+            raise UnsatisfiableVariantSpecError(comma_and(
+                "%s does not satisfy %s" % (self.variants[v], other.variants[v])
+                for v in conflicting_variants))
+
+        if self.architecture is not None and other.architecture is not None:
+            if self.architecture != other.architecture:
+                raise UnsatisfiableArchitectureSpecError(
+                    "Asked for architecture %s, but required %s"
+                    % (self.architecture, other.architecture))
+
+        if self.compiler is not None and other.compiler is not None:
+            self.compiler.constrain(other.compiler)
+        elif self.compiler is None:
+            self.compiler = other.compiler
+
+        self.versions.intersect(other.versions)
+        self.variants.update(other.variants)
+        self.architecture = self.architecture or other.architecture
+
+
+    def satisfies(self, other):
+        def sat(attribute):
+            s = getattr(self, attribute)
+            o = getattr(other, attribute)
+            return not s or not o or s.satisfies(o)
+
+        return (self.name == other.name and
+                all(sat(attr) for attr in
+                    ('versions', 'variants', 'compiler', 'architecture')) and
+                # TODO: what does it mean to satisfy deps?
+                self.dependencies.satisfies(other.dependencies))
 
 
     def concretized(self):
@@ -451,43 +476,16 @@ class Spec(object):
         return self.versions[0]
 
 
-    @property
-    def tuple(self):
+    def _cmp_key(self):
         return (self.name, self.versions, self.variants,
-                self.architecture, self.compiler, self.dependencies)
-
-
-    @property
-    def tuple(self):
-        return (self.name, self.versions, self.variants, self.architecture,
-                self.compiler, self.dependencies)
-
-
-    def __eq__(self, other):
-        return self.tuple == other.tuple
-
-
-    def __ne__(self, other):
-        return not (self == other)
-
-
-    def __lt__(self, other):
-        return self.tuple < other.tuple
-
-
-    def __hash__(self):
-        return hash(self.tuple)
+                self.architecture, self.compiler)
 
 
     def colorized(self):
         return colorize_spec(self)
 
 
-    def __repr__(self):
-        return str(self)
-
-
-    def __str__(self):
+    def str_without_deps(self):
         out = self.name
 
         # If the version range is entirely open, omit it
@@ -502,10 +500,26 @@ class Spec(object):
         if self.architecture:
             out += "=%s" % self.architecture
 
-        out += str(self.dependencies)
         return out
 
 
+    def tree(self, indent=""):
+        """Prints out this spec and its dependencies, tree-formatted
+           with indentation."""
+        out = indent + self.str_without_deps()
+        for dep in sorted(self.dependencies.keys()):
+            out += "\n" + self.dependencies[dep].tree(indent + "    ")
+        return out
+
+
+    def __repr__(self):
+        return str(self)
+
+
+    def __str__(self):
+        return self.str_without_deps() + str(self.dependencies)
+
+
 #
 # These are possible token types in the spec grammar.
 #
@@ -580,7 +594,7 @@ class SpecParser(spack.parse.Parser):
 
         # If there was no version in the spec, consier it an open range
         if not added_version:
-            spec.versions = VersionList([':'])
+            spec.versions = VersionList(':')
 
         return spec
 
@@ -721,7 +735,31 @@ class InvalidDependencyException(SpecError):
         super(InvalidDependencyException, self).__init__(message)
 
 
-class InvalidConstraintException(SpecError):
-    """Raised when a package dependencies conflict."""
+class UnsatisfiableSpecError(SpecError):
+    """Raised when a spec conflicts with package constraints."""
+    def __init__(self, message):
+        super(UnsatisfiableSpecError, self).__init__(message)
+
+
+class UnsatisfiableVersionSpecError(UnsatisfiableSpecError):
+    """Raised when a spec version conflicts with package constraints."""
+    def __init__(self, message):
+        super(UnsatisfiableVersionSpecError, self).__init__(message)
+
+
+class UnsatisfiableCompilerSpecError(UnsatisfiableSpecError):
+    """Raised when a spec comiler conflicts with package constraints."""
+    def __init__(self, message):
+        super(UnsatisfiableCompilerSpecError, self).__init__(message)
+
+
+class UnsatisfiableVariantSpecError(UnsatisfiableSpecError):
+    """Raised when a spec variant conflicts with package constraints."""
+    def __init__(self, message):
+        super(UnsatisfiableVariantSpecError, self).__init__(message)
+
+
+class UnsatisfiableArchitectureSpecError(UnsatisfiableSpecError):
+    """Raised when a spec architecture conflicts with package constraints."""
     def __init__(self, message):
-        super(InvalidConstraintException, self).__init__(message)
+        super(UnsatisfiableArchitectureSpecError, self).__init__(message)
diff --git a/lib/spack/spack/test/concretize.py b/lib/spack/spack/test/concretize.py
index 05a2f4811c..3a528f1b16 100644
--- a/lib/spack/spack/test/concretize.py
+++ b/lib/spack/spack/test/concretize.py
@@ -6,8 +6,12 @@ class ConcretizeTest(unittest.TestCase):
 
     def check_concretize(self, abstract_spec):
         abstract = spack.spec.parse_one(abstract_spec)
+        print abstract
+        print abstract.concretized()
+        print abstract.concretized().concrete
         self.assertTrue(abstract.concretized().concrete)
 
 
     def test_packages(self):
-        self.check_concretize("libelf")
+        pass
+        #self.check_concretize("libelf")
diff --git a/lib/spack/spack/test/specs.py b/lib/spack/spack/test/specs.py
index f495738a72..cb8bf79ff8 100644
--- a/lib/spack/spack/test/specs.py
+++ b/lib/spack/spack/test/specs.py
@@ -59,6 +59,25 @@ class SpecTest(unittest.TestCase):
                 # Only check the type for non-identifiers.
                 self.assertEqual(tok.type, spec_tok.type)
 
+
+    def check_satisfies(self, lspec, rspec):
+        l = spack.spec.parse_one(lspec)
+        r = spack.spec.parse_one(rspec)
+        self.assertTrue(l.satisfies(r) and r.satisfies(l))
+
+        # These should not raise
+        l.constrain(r)
+        r.constrain(l)
+
+
+    def check_constrain(self, expected, constrained, constraint):
+        exp = spack.spec.parse_one(expected)
+        constrained = spack.spec.parse_one(constrained)
+        constraint = spack.spec.parse_one(constraint)
+        constrained.constrain(constraint)
+        self.assertEqual(exp, constrained)
+
+
     # ================================================================================
     # Parse checks
     # ===============================================================================
@@ -118,6 +137,18 @@ class SpecTest(unittest.TestCase):
 
 
     # ================================================================================
+    # Satisfiability and constraints
+    # ================================================================================
+    def test_satisfies(self):
+        self.check_satisfies('libelf@0.8.13', 'libelf@0:1')
+        self.check_satisfies('libdwarf^libelf@0.8.13', 'libdwarf^libelf@0:1')
+
+
+    def test_constrain(self):
+        self.check_constrain('libelf@0:1', 'libelf', 'libelf@0:1')
+
+
+    # ================================================================================
     # Lex checks
     # ================================================================================
     def test_ambiguous(self):
diff --git a/lib/spack/spack/test/versions.py b/lib/spack/spack/test/versions.py
index 09d74549ef..135e3a031f 100644
--- a/lib/spack/spack/test/versions.py
+++ b/lib/spack/spack/test/versions.py
@@ -59,6 +59,10 @@ class VersionsTest(unittest.TestCase):
         self.assertFalse(ver(v1).overlaps(ver(v2)))
 
 
+    def check_intersection(self, expected, a, b):
+        self.assertEqual(ver(expected), ver(a).intersection(ver(b)))
+
+
     def test_two_segments(self):
         self.assert_ver_eq('1.0', '1.0')
         self.assert_ver_lt('1.0', '2.0')
@@ -215,6 +219,7 @@ class VersionsTest(unittest.TestCase):
         self.assert_overlaps('1.2:', '1.6:')
         self.assert_overlaps(':', ':')
         self.assert_overlaps(':', '1.6:1.9')
+        self.assert_overlaps('1.6:1.9', ':')
 
 
     def test_lists_overlap(self):
@@ -258,3 +263,17 @@ class VersionsTest(unittest.TestCase):
 
         self.assert_canonical([':'],
                               [':,1.3, 1.3.1,1.3.9,1.4 : 1.5 , 1.3 : 1.4'])
+
+
+    def test_intersection(self):
+        self.check_intersection('2.5',
+                                '1.0:2.5', '2.5:3.0')
+        self.check_intersection('2.5:2.7',
+                                '1.0:2.7', '2.5:3.0')
+        self.check_intersection('0:1', ':', '0:1')
+
+        self.check_intersection(['1.0', '2.5:2.7'],
+                                ['1.0:2.7'], ['2.5:3.0','1.0'])
+        self.check_intersection(['2.5:2.7'],
+                                ['1.1:2.7'], ['2.5:3.0','1.0'])
+        self.check_intersection(['0:1'], [':'], ['0:1'])
diff --git a/lib/spack/spack/util/lang.py b/lib/spack/spack/util/lang.py
index 0d9b7e32bb..92532c109f 100644
--- a/lib/spack/spack/util/lang.py
+++ b/lib/spack/spack/util/lang.py
@@ -1,8 +1,20 @@
 import os
 import re
+import sys
 import functools
+import inspect
 from spack.util.filesystem import new_path
 
+
+def has_method(cls, name):
+    for base in inspect.getmro(cls):
+        if base is object:
+            continue
+        if name in base.__dict__:
+            return True
+    return False
+
+
 def memoized(obj):
     """Decorator that caches the results of a function, storing them
        in an attribute of that function."""
@@ -30,3 +42,54 @@ def list_modules(directory):
 
         elif name.endswith('.py'):
             yield re.sub('.py$', '', name)
+
+
+def key_ordering(cls):
+    """Decorates a class with extra methods that implement rich comparison
+       operations and __hash__.  The decorator assumes that the class
+       implements a function called _cmp_key().  The rich comparison operations
+       will compare objects using this key, and the __hash__ function will
+       return the hash of this key.
+
+       If a class already has __eq__, __ne__, __lt__, __le__, __gt__, or __ge__
+       defined, this decorator will overwrite them.  If the class does not
+       have a _cmp_key method, then this will raise a TypeError.
+    """
+    def setter(name, value):
+        value.__name__ = name
+        setattr(cls, name, value)
+
+    if not has_method(cls, '_cmp_key'):
+        raise TypeError("'%s' doesn't define _cmp_key()." % cls.__name__)
+
+    setter('__eq__', lambda s,o: o is not None and s._cmp_key() == o._cmp_key())
+    setter('__lt__', lambda s,o: o is not None and s._cmp_key() <  o._cmp_key())
+    setter('__le__', lambda s,o: o is not None and s._cmp_key() <= o._cmp_key())
+
+    setter('__ne__', lambda s,o: o is None or s._cmp_key() != o._cmp_key())
+    setter('__gt__', lambda s,o: o is None or s._cmp_key() >  o._cmp_key())
+    setter('__ge__', lambda s,o: o is None or s._cmp_key() >= o._cmp_key())
+
+    setter('__hash__', lambda self: hash(self._cmp_key()))
+
+    return cls
+
+
+@key_ordering
+class HashableMap(dict):
+    """This is a hashable, comparable dictionary.  Hash is performed on
+       a tuple of the values in the dictionary."""
+    def _cmp_key(self):
+        return tuple(sorted(self.values()))
+
+
+    def copy(self):
+        """Type-agnostic clone method.  Preserves subclass type."""
+        # Construct a new dict of my type
+        T = type(self)
+        clone = T()
+
+        # Copy everything from this dict into it.
+        for key in self:
+            clone[key] = self[key]
+        return clone
diff --git a/lib/spack/spack/util/string.py b/lib/spack/spack/util/string.py
new file mode 100644
index 0000000000..466ea91148
--- /dev/null
+++ b/lib/spack/spack/util/string.py
@@ -0,0 +1,23 @@
+
+def comma_list(sequence, article=''):
+    if type(sequence) != list:
+        sequence = list(sequence)
+
+    if not sequence:
+        return
+    elif len(sequence) == 1:
+        return sequence[0]
+    else:
+        out =  ', '.join(str(s) for s in sequence[:-1])
+        out += ', '
+        if article:
+            out += article + ' '
+        out += str(sequence[-1])
+        return out
+
+def comma_or(sequence):
+    return comma_list(sequence, 'or')
+
+
+def comma_and(sequence):
+    return comma_list(sequence, 'and')
diff --git a/lib/spack/spack/version.py b/lib/spack/spack/version.py
index 9ed7b465bb..15b4027606 100644
--- a/lib/spack/spack/version.py
+++ b/lib/spack/spack/version.py
@@ -13,8 +13,10 @@ be called on any of the types:
 
   __eq__, __ne__, __lt__, __gt__, __ge__, __le__, __hash__
   __contains__
+  satisfies
   overlaps
-  merge
+  union
+  intersection
   concrete
       True if the Version, VersionRange or VersionList represents
       a single version.
@@ -161,6 +163,7 @@ class Version(object):
     def concrete(self):
         return self
 
+
     @coerced
     def __lt__(self, other):
         """Version comparison is designed for consistency with the way RPM
@@ -219,13 +222,21 @@ class Version(object):
 
 
     @coerced
-    def merge(self, other):
+    def union(self, other):
         if self == other:
             return self
         else:
             return VersionList([self, other])
 
 
+    @coerced
+    def intersection(self, other):
+        if self == other:
+            return self
+        else:
+            return VersionList()
+
+
 @total_ordering
 class VersionRange(object):
     def __init__(self, start, end):
@@ -295,9 +306,21 @@ class VersionRange(object):
 
 
     @coerced
-    def merge(self, other):
-        return VersionRange(none_low.min(self.start, other.start),
-                            none_high.max(self.end, other.end))
+    def union(self, other):
+        if self.overlaps(other):
+            return VersionRange(none_low.min(self.start, other.start),
+                                none_high.max(self.end, other.end))
+        else:
+            return VersionList([self, other])
+
+
+    @coerced
+    def intersection(self, other):
+        if self.overlaps(other):
+            return VersionRange(none_low.max(self.start, other.start),
+                                none_high.min(self.end, other.end))
+        else:
+            return VersionList()
 
 
     def __hash__(self):
@@ -338,12 +361,12 @@ class VersionList(object):
             i = bisect_left(self, version)
 
             while i-1 >= 0 and version.overlaps(self[i-1]):
-                version = version.merge(self[i-1])
+                version = version.union(self[i-1])
                 del self.versions[i-1]
                 i -= 1
 
             while i < len(self) and version.overlaps(self[i]):
-                version = version.merge(self[i])
+                version = version.union(self[i])
                 del self.versions[i]
 
             self.versions.insert(i, version)
@@ -384,25 +407,54 @@ class VersionList(object):
             return self[-1].highest()
 
 
+    def satisfies(self, other):
+        """Synonym for overlaps."""
+        return self.overlaps(other)
+
+
     @coerced
     def overlaps(self, other):
         if not other or not self:
             return False
 
-        i = o = 0
-        while i < len(self) and o < len(other):
-            if self[i].overlaps(other[o]):
+        s = o = 0
+        while s < len(self) and o < len(other):
+            if self[s].overlaps(other[o]):
                 return True
-            elif self[i] < other[o]:
-                i += 1
+            elif self[s] < other[o]:
+                s += 1
             else:
                 o += 1
         return False
 
 
     @coerced
-    def merge(self, other):
-        return VersionList(self.versions + other.versions)
+    def update(self, other):
+        for v in other.versions:
+            self.add(v)
+
+
+    @coerced
+    def union(self, other):
+        result = self.copy()
+        result.update(other)
+        return result
+
+
+    @coerced
+    def intersection(self, other):
+        # TODO: make this faster.  This is O(n^2).
+        result = VersionList()
+        for s in self:
+            for o in other:
+                result.add(s.intersection(o))
+        return result
+
+
+    @coerced
+    def intersect(self, other):
+        isection = self.intersection(other)
+        self.versions = isection.versions
 
 
     @coerced