provide directory existence feedback to user

instead of bailing with an obnoxious error message, or silently ignoring a
command-line option of a directory, squawk to STDERR with the problem and
provide (possibly redundant, but maybe informative) traceback

tests/test_config.py

@@ -21,5 +21,12 @@ class TestConfigWorks(unittest.TestCase):
         config, args = collectconfiguration('tag', ['--pubdir', '.'])
         self.assertEqual(config.pubdir, '.')
 
+    def test_nonexistent_directory(self):
+        argv = ['--pubdir', '/path/to/nonexistent/directory']
+        with self.assertRaises(ValueError) as ecm:
+            config, args = collectconfiguration('tag', argv)
+        e = ecm.exception
+        self.assertTrue("/path/to/nonexistent/directory" in e.args[0])
+
 #
 # -- end of file

tldp/config.py

@@ -4,9 +4,13 @@
 from __future__ import absolute_import, division, print_function
 from __future__ import unicode_literals
 
+import os
+import argparse
+import copy as _copy
+
 import logging
 
-from tldp.utils import arg_isdirectory, arg_isloglevel, arg_isreadablefile
+from tldp.utils import arg_isloglevel, arg_isreadablefile
 from tldp.cascadingconfig import CascadingConfig, DefaultFreeArgumentParser
 
 import tldp.typeguesser
@@ -16,6 +20,30 @@ logger = logging.getLogger(__name__)
 DEFAULT_CONFIGFILE = '/etc/ldptool/ldptool.ini'
 
 
+class DirectoriesExist(argparse._AppendAction):
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        if not os.path.isdir(values):
+            message = "No such directory: %r for option %r, removing..."
+            message = message % (values, option_string)
+            logger.critical(message)
+            raise ValueError(message)
+        items = _copy.copy(argparse._ensure_value(namespace, self.dest, []))
+        items.append(values)
+        setattr(namespace, self.dest, items)
+
+
+class DirectoryExists(argparse._StoreAction):
+
+    def __call__(self, parser, namespace, values, option_string=None):
+        if not os.path.isdir(values):
+            message = "No such directory: %r for option %r, removing..."
+            message = message % (values, option_string)
+            logger.critical(message)
+            raise ValueError(message)
+        setattr(namespace, self.dest, values)
+
+
 def collectconfiguration(tag, argv):
     ap = DefaultFreeArgumentParser()
 
@@ -63,15 +91,15 @@ def collectconfiguration(tag, argv):
                     help='subdirs to copy during build [%(default)s]')
     ap.add_argument('--sourcedir', '--source-dir', '--source-directory',
                     '-s',
-                    action='append', default='', type=arg_isdirectory,
+                    default=[], action=DirectoriesExist,
                     help='a directory containing LDP source documents')
     ap.add_argument('--pubdir', '--output', '--outputdir', '--outdir',
                     '-o',
-                    default=None, type=arg_isdirectory,
+                    default=None, action=DirectoryExists,
                     help='a directory containing LDP output documents')
     ap.add_argument('--builddir', '--build-dir', '--build-directory',
                     '-d',
-                    default=None, type=arg_isdirectory,
+                    default=None, action=DirectoryExists,
                     help='a scratch directory used for building')
     ap.add_argument('--configfile', '--config-file', '--cfg',
                     '-c',