Index: /trunk/packages/invirt-base/debian/changelog
===================================================================
--- /trunk/packages/invirt-base/debian/changelog	(revision 1933)
+++ /trunk/packages/invirt-base/debian/changelog	(revision 1934)
@@ -4,6 +4,7 @@
   * config-init.sh: degrade to non-bash gracefully, document better
   * invirt.config: fix an error on empty config files
-
- -- Greg Price <price@mit.edu>  Sun, 28 Dec 2008 19:16:03 -0500
+  * invirt.common: give clearer error message on missing config variable
+
+ -- Greg Price <price@mit.edu>  Sun, 28 Dec 2008 19:18:51 -0500
 
 invirt-base (0.0.17) unstable; urgency=low
Index: /trunk/packages/invirt-base/python/invirt/common.py
===================================================================
--- /trunk/packages/invirt-base/python/invirt/common.py	(revision 1933)
+++ /trunk/packages/invirt-base/python/invirt/common.py	(revision 1934)
@@ -5,20 +5,39 @@
 import contextlib as clib
 
+class InvirtConfigError(AttributeError):
+    pass
+
 class struct(object):
     'A simple namespace object.'
-    def __init__(self, d = {}, **kwargs):
-        'd is the dictionary to update my __dict__ with.'
+    def __init__(self, d = {}, __prefix = None, **kwargs):
+        'd is the dictionary or the items-iterable to update my __dict__ with.'
         self.__dict__.update(d)
         self.__dict__.update(kwargs)
+        self.__prefix = __prefix
+    def __getattr__(self, key):
+        # XX ideally these would point a frame higher on the stack.
+        prefix = self.__prefix
+        if prefix is not None:
+            raise InvirtConfigError('missing configuration variable %s%s'
+                                    % (prefix, key))
+        else:
+            raise AttributeError("anonymous struct has no member '%s'"
+                                 % (key,))
 
-def dicts2struct(x):
+def dicts2struct(x, prefix = None):
     """
     Given a tree of lists/dicts, perform a deep traversal to transform all the
     dicts to structs.
     """
+    if prefix is not None:
+        def newprefix(k): return prefix + str(k) + '.'
+    else:
+        def newprefix(k): return prefix
     if type(x) == dict:
-        return struct((k, dicts2struct(v)) for k,v in x.iteritems())
+        return struct(((k, dicts2struct(v, newprefix(k)))
+                       for k,v in x.iteritems()),
+                      prefix)
     elif type(x) == list:
-        return [dicts2struct(v) for v in x]
+        return [dicts2struct(v, newprefix(i)) for i, v in enumerate(x)]
     else:
         return x
@@ -68,5 +87,5 @@
                 'list': [ 'atom', {'key': 'value'} ]
                 }
-        structs = dicts2struct(dicts)
+        structs = dicts2struct(dicts, '')
         self.assertEqual(structs.atom,        dicts['atom'])
         self.assertEqual(structs.dict.atom,   dicts['dict']['atom'])
Index: /trunk/packages/invirt-base/python/invirt/config.py
===================================================================
--- /trunk/packages/invirt-base/python/invirt/config.py	(revision 1933)
+++ /trunk/packages/invirt-base/python/invirt/config.py	(revision 1934)
@@ -141,5 +141,5 @@
 
 dicts = load()
-structs = dicts2struct(dicts)
+structs = dicts2struct(dicts, '')
 
 # vim:et:sw=4:ts=4