Better spack -h: added cmd descriptions.

- each cmd has a desscription attribute that is used for the help strign in argparse.

lib/spack/spack/cmd/__init__.py

@@ -3,11 +3,14 @@
 
 import spack
 import spack.tty as tty
+import spack.attr as attr
 
 # Patterns to ignore in the commands directory when looking for commands.
 ignore_files = r'^\.|^__init__.py$|^#'
 
-setup_parser = "setup_parser"
+SETUP_PARSER = "setup_parser"
+DESCRIPTION  = "description"
+
 command_path = os.path.join(spack.lib_path, "spack", "cmd")
 
 commands = []
@@ -25,8 +28,12 @@ def null_op(*args):
 def get_module(name):
     """Imports the module for a particular command name and returns it."""
     module_name = "%s.%s" % (__name__, name)
-    module = __import__(module_name, fromlist=[name, setup_parser], level=0)
-    module.setup_parser = getattr(module, setup_parser, null_op)
+    module = __import__(
+        module_name, fromlist=[name, SETUP_PARSER, DESCRIPTION],
+        level=0)
+
+    attr.setdefault(module, SETUP_PARSER, null_op)
+    attr.setdefault(module, DESCRIPTION, "")
 
     if not hasattr(module, name):
         tty.die("Command module %s (%s) must define function '%s'."

lib/spack/spack/cmd/clean.py

@@ -2,6 +2,8 @@
 import spack.tty as tty
 import spack.stage as stage
 
+description = "Remove staged files for packages"
+
 def setup_parser(subparser):
     subparser.add_argument('names', nargs='+', help="name(s) of package(s) to clean")
     subparser.add_argument('-c', "--clean", action="store_true", dest='clean',

lib/spack/spack/cmd/create.py

@@ -9,6 +9,8 @@
 from spack.stage import Stage
 from contextlib import closing
 
+description = "Create a new package file from an archive URL"
+
 package_template = string.Template("""\
 from spack import *
 

lib/spack/spack/cmd/edit.py

@@ -3,6 +3,7 @@
 import spack.packages as packages
 import spack.tty as tty
 
+description = "Open package files in $EDITOR"
 
 def setup_parser(subparser):
     subparser.add_argument(

lib/spack/spack/cmd/fetch.py

@@ -1,5 +1,7 @@
 import spack.packages as packages
 
+description = "Fetch archives for packages"
+
 def setup_parser(subparser):
     subparser.add_argument('name', help="name of package to fetch")
     subparser.add_argument('-f', '--file', dest='file', default=None,

lib/spack/spack/cmd/graph.py

@@ -1,6 +1,7 @@
 import spack
 import spack.packages as packages
 
+description = "Write out inter-package dependencies in dot graph format"
 
 def graph(parser, args):
     packages.graph_dependencies()

lib/spack/spack/cmd/help.py

@@ -1,5 +1,7 @@
 import sys
 
+description = "Get help on spack and its commands"
+
 def setup_parser(subparser):
     subparser.add_argument('help_command', nargs='?', default=None,
                            help='command to get help on')

lib/spack/spack/cmd/install.py

@@ -1,6 +1,8 @@
 import spack
 import spack.packages as packages
 
+description = "Build and install packages"
+
 def setup_parser(subparser):
     subparser.add_argument('names', nargs='+', help="name(s) of package(s) to install")
     subparser.add_argument('-i', '--ignore-dependencies',

lib/spack/spack/cmd/list.py

@@ -2,6 +2,7 @@
 import spack.packages as packages
 from spack.colify import colify
 
+description ="List spack packages"
 
 def setup_parser(subparser):
     subparser.add_argument('-i', '--installed', action='store_true', dest='installed',

lib/spack/spack/cmd/purge.py

@@ -1,4 +1,6 @@
 import spack.stage as stage
 
+description = "Remove all temporary build files and downloaded archives"
+
 def purge(parser, args):
     stage.purge()

lib/spack/spack/cmd/stage.py

@@ -1,5 +1,7 @@
 import spack.packages as packages
 
+description="Expand downloaded archive in preparation for install"
+
 def setup_parser(subparser):
     subparser.add_argument('name', help="name of package to stage")
 

lib/spack/spack/cmd/uninstall.py

@@ -1,5 +1,7 @@
 import spack.packages as packages
 
+description="Remove an installed package"
+
 def setup_parser(subparser):
     subparser.add_argument('names', nargs='+', help="name(s) of package(s) to uninstall")
     subparser.add_argument('-f', '--force', action='store_true', dest='force',