1 files changed, 24 insertions, 1 deletions
diff --git a/lib/spack/spack/packages/__init__.py b/lib/spack/spack/packages/__init__.py
index 8692dde5a8..40270afc99 100644
--- a/lib/spack/spack/packages/__init__.py
+++ b/lib/spack/spack/packages/__init__.py
@@ -19,6 +19,7 @@ valid_package_re = r'^\w[\w-]*$'
 invalid_package_re = r'[_-][_-]+'
 
 instances = {}
+providers = {}
 
 
 def get(pkg_name):
@@ -29,6 +30,24 @@ def get(pkg_name):
     return instances[pkg_name]
 
 
+def get_providers(vpkg_name):
+    if not providers:
+        compute_providers()
+
+    if not vpkg_name in providers:
+        raise UnknownPackageError("No such virtual package: %s" % vpkg_name)
+
+    return providers[vpkg_name]
+
+
+def compute_providers():
+    for pkg in all_packages():
+        for vpkg in pkg.provided_virtual_packages:
+            if vpkg not in providers:
+                providers[vpkg] = []
+            providers[vpkg].append(pkg)
+
+
 def valid_package_name(pkg_name):
     return (re.match(valid_package_re, pkg_name) and
             not re.search(invalid_package_re, pkg_name))
@@ -75,6 +94,11 @@ def class_name_for_package_name(pkg_name):
     return class_name
 
 
+def exists(pkg_name):
+    """Whether a package is concrete."""
+    return os.path.exists(filename_for_package_name(pkg_name))
+
+
 def get_class_for_package_name(pkg_name):
     file_name = filename_for_package_name(pkg_name)
 
@@ -149,7 +173,6 @@ def graph_dependencies(out=sys.stdout):
     out.write('}\n')
 
 
-
 class InvalidPackageNameError(spack.error.SpackError):
     """Raised when we encounter a bad package name."""
     def __init__(self, name):